The Cooling Thread

[C-Kwik]

*EDIT*

We don't really have a thread dedicated to cooling and it came up in another discussion so I figured I'd split the thread so as to stay on topic etc.

WD

************************************************************

- A 16.8lb Nismo radiator cap

A higher pressure radiator cap doesn't increase cooling capacity unless a person is boiling the coolant with a standard cap (in which case pockets of vapor will reduce the contact area with the motor). If you are unable to keep your engine temp in the normal range (assuming everything is working as designed), then you likely need a radiator upgrade. Where I might concede is if the radiator is sufficient in size to bring the coolant temp near ambient but enough heat is generated such that the coolant simply can't carry enough heat out fast enough. Its a band-aid to a bigger problem either way, but short of going in and trying to redesigning cooling passages (impractical), its the only real option left to try and help prevent the fluid from boiling. However, this is an unlikely scenario for modern motors. Its more of a see if it happens and respond type of mod anyways. If one's cooling system is working fine with the standard cap, a higher pressure one will have zero benefit.

EDIT: I just read over the list again and I'd probably throw BOV into the "required" sections. While BOV's aren't absolutely necessary to make it work, relatively few people are going to be investing in BB turbos that can handle the higher thrust loads associated with compressor surge. I'd rather they buy and install a BOV than be replacing or rebuilding turbos all the time.

[PapaSmurf2k3]

EDIT: I just read over the list again and I'd probably throw BOV into the "required" sections. While BOV's aren't absolutely necessary to make it work, relatively few people are going to be investing in BB turbos that can handle the higher thrust loads associated with compressor surge. I'd rather they buy and install a BOV than be replacing or rebuilding turbos all the time.

Yeah, when I wrote it up there were some things that I definitely thought SHOULD be done, but if you think about it, aren't absolutely required. I would think the majority of the people that would use this list would be newbs, most of which will never attempt to build a KA-T anyway. I would hope someone gunning for a monster KA-T setup would do a little more research than just looking at this list and taking it as gospel.

This is like the same thing on ka-t.org.

YES IT IS!!! Someone actually linked me to their thread almost immediately after I posted this one. I didn't read all of it, but theirs definitely looks more in-depth. There will most likely be some changes made to this one as people post suggestions. It will eventually be added to the sticky list and FAQ.

May I suggest adding:

- 'Colder' spark plugs- A 16.8lb Nismo radiator cap- Heat shielding for the turbo so you don't roast the brake fluid resevior- Gauges like Oil Temp and Press, boost, AFR ... - Adjustatble fuel pressure regulator, 'quality' fuel filter (no paper), upgraded fuel lines, larger fuel rail.- Larger cams- Heat porting- Maybe a driveshaft loop for safety- Some sort of fire extinguishing capability whether on-board or hand held- T-bolt clamps on all piping connections and a bead welded to the edge of the charge pipes so the clamps have something help grip on

Yes, some of the above may be 'power' specific, but then I'm in the 400+ club.

I'm surprised I left some of that stuff out. Does anyone know the standard set of rules for a track? Like once you break into the 11's, you are required to have a roll cage and a fire extinguisher, etc?

[scotty-2-forty]

A higher pressure radiator cap doesn't increase cooling capacity unless a person is boiling the coolant with a standard cap (in which case pockets of vapor will reduce the contact area with the motor). If you are unable to keep your engine temp in the normal range (assuming everything is working as designed), then you likely need a radiator upgrade. Where I might concede is if the radiator is sufficient in size to bring the coolant temp near ambient but enough heat is generated such that the coolant simply can't carry enough heat out fast enough. Its a band-aid to a bigger problem either way, but short of going in and trying to redesigning cooling passages (impractical), its the only real option left to try and help prevent the fluid from boiling. However, this is an unlikely scenario for modern motors. Its more of a see if it happens and respond type of mod anyways. If one's cooling system is working fine with the standard cap, a higher pressure one will have zero benefit.

EDIT: I just read over the list again and I'd probably throw BOV into the "required" sections. While BOV's aren't absolutely necessary to make it work, relatively few people are going to be investing in BB turbos that can handle the higher thrust loads associated with compressor surge. I'd rather they buy and install a BOV than be replacing or rebuilding turbos all the time.

Actually, I mispoke ... I meant even higher. I have the GReddy 127kPa (18.4 PSI). A higher pressure equates to a higher boiling point for the coolant, yes. But higher coolant pressures also transfer heat from the cylinder head more efficiently. Most OEM radiator caps release pressure at about 15 PSI. By installing a higher PSI radiator cap you can further increase the boiling point of your engines coolant. This will allow you to run in higher ambient temperatures without the worry of your cooling system boiling over. I run a Koyo radiator that provides 20-30% more cooling over stock, and run the GReddy 18.4 PSI cap. Nice balance when running her hard. But in any event C-Kwik, I think we are more-or-less stating the same thing here. PapaSmurf said it best in stating that he hopes newbs don't just take this as gospel for their otherwise guesstimate build. So this might be a good insurance policy too.

I second the BOV statement.

Oh, and Papa ... you might want to put in some sort of disclaimer that this is only for reference and not to be used as 'gospel', and NICOclub does not warrant nor express any ... blah-blah-blah ... in other words, if a person doesn't know what they're doing, seek the assistance of a professional. Just a thought.
Modified by scotty-2-forty at 10:01 PM 3/15/2010

[C-Kwik]

Yeah, when I wrote it up there were some things that I definitely thought SHOULD be done, but if you think about it, aren't absolutely required. I would think the majority of the people that would use this list would be newbs, most of which will never attempt to build a KA-T anyway. I would hope someone gunning for a monster KA-T setup would do a little more research than just looking at this list and taking it as gospel.

While I don't disagree that this is just a guide, the kind of people who need such a list may not comprehensively know what each part does. To put it frankly, I wouldn't recommend anyone running a turbo not run a BOV UNLESS they know what they are doing. Just erring on the side of caution.

Actually, I mispoke ... I meant even higher. I have the GReddy 127kPa (18.4 PSI). A higher pressure equates to a higher boiling point for the coolant, yes. But higher coolant pressures also transfer heat from the cylinder head more efficiently. Most OEM radiator caps release pressure at about 15 PSI. By installing a higher PSI radiator cap you can further increase the boiling point of your engines coolant. This will allow you to run in higher ambient temperatures without the worry of your cooling system boiling over. I run a Koyo radiator that provides 20-30% more cooling over stock, and run the GReddy 18.4 PSI cap. Nice balance when running her hard. But in any event C-Kwik, I think we are more-or-less stating the same thing here.

Nope, not saying the same thing at all. The specific heat of water does not change with the pressure of water. That means a given mass of water, can only absorb a certain amount of heat energy before it boils. Since water and liquids are not really all that compressible, the density (mass per unit volume) will not change. As a result, there will be no difference in how much heat a higher pressure coolant will carry away.

The exception here is if the engine runs hot enough such that it exceeds the running capacity for the coolant to carry away the excess heat to the point that the coolant boils. When said coolant boils, it turns into a vapor (a gas) which has lower heat transfer properties and a lower specific heat by volume. But if the cooling capacity is not exceeded a higher pressure cap will do nothing but look pretty and add to your list of mods.

But more practically, most cooling passages in modern motors are likely to be able to handle quite a bit of heat rejection so long as the coolant temperature entering the motor is low enough and maximum flow is high enough. Also consider, a motor that utilizes a higher pressure radiator cap's benefits will actually be running at a hotter temp when it does use the benefits. Unless you've engineered the motor to run at a hotter temp its probably not a good idea. Not to mention high boost motors aren't going to be as detonation friendly if the operating temperature is higher...

[scotty-2-forty]

Nope, not saying the same thing at all. The specific heat of water does not change with the pressure of water. That means a given mass of water, can only absorb a certain amount of heat energy before it boils. Since water and liquids are not really all that compressible, the density (mass per unit volume) will not change. As a result, there will be no difference in how much heat a higher pressure coolant will carry away. ...

C-Kwik, I did not say that the heat of water changes with increased pressure. I said that "a higher pressure equates to a higher boiling point for the coolant." As the coolant mixture heats up it will expand, thus it builds pressure. In other words, its boiling point increases when it is placed under pressure. We know the radiator cap's duty is to relieve the pressure at a certain 'pressure', not temperature.

The exception here is if the engine runs hot enough such that it exceeds the running capacity for the coolant to carry away the excess heat to the point that the coolant boils. When said coolant boils, it turns into a vapor (a gas) which has lower heat transfer properties and a lower specific heat by volume. But if the cooling capacity is not exceeded a higher pressure cap will do nothing but look pretty and add to your list of mods. ...

Pretty is good! What's wrong with pretty? Seriously though, but by increasing the opening pressure of the radiator cap's regulator to allow higher radiator pressure it will in effect increase the boiling point of the coolant and reduce bubbles in the coolant system. In turn it improves cooling by circulating liquid and not air, and generally maximizes the cooling performance of the radiator. Everyone knows (at least we do) that air in the coolant passages is not good. Now I should say we are in agreement that the cap should be matched to the radiator being used. I brought up the higher pressure rated cap based on the use of a performance radiator which I could have been a bit more clear; I am basing it on the 300+ crowd which like Papa said it is suggested to upgrade to a racing radiator. Performance radiators are typically rated 22-24 PSI, and professional racing radiators at 29-31 PSI (give or take a few PSI). The highest pressure rated radiator cap that your radiator will accept should always be used. I just wouldn't call it a "band-aid"; it should more be considered a safety net, as once the car overheats by relieving the pressure set by the cap's valve it should be immediately shut down to come to a cool properly. All this brings to light too, it's not a bad idea to upgarde the water pump, to quicken the pace of heat reduction from the engine components through the radiator.

But more practically, most cooling passages in modern motors are likely to be able to handle quite a bit of heat rejection so long as the coolant temperature entering the motor is low enough and maximum flow is high enough. Also consider, a motor that utilizes a higher pressure radiator cap's benefits will actually be running at a hotter temp when it does use the benefits. Unless you've engineered the motor to run at a hotter temp its probably not a good idea. Not to mention high boost motors aren't going to be as detonation friendly if the operating temperature is higher...

Performance engines are always going to run higher temperatures due to lots of variables ... it's the nature of the game, thus the reason for the cooling system upgrade(s). I think a good point here is that if one is going to build a higher powered KA engine such as 300hp and up, all of these things need to be seriously considered. BTW, this is a great thread!
Modified by scotty-2-forty at 8:20 PM 3/16/2010

[PapaSmurf2k3]

I've seen 240s with boiling coolant... Most recently at Carlisle last year.

[C-Kwik]

C-Kwik, I did not say that the heat of water changes with increased pressure. I said that "a higher pressure equates to a higher boiling point for the coolant." As the coolant mixture heats up it will expand, thus it builds pressure. In other words, its boiling point increases when it is placed under pressure. We know the radiator cap's duty is to relieve the pressure at a certain 'pressure', not temperature.

I did not say the heat changes with temperature. I said the SPECIFIC heat does not change with temperature. Your statement that coolant under higher pressure can "transfer heat from the cylinder head more efficiently" implies otherwise. Since heat only transfers when there is a difference in temperature and the amount of heat that transfers is related to the amount of heat the medium can absorb until the temperatures become equal (which is what specific heat deals with), a higher pressure liquid will not be able to absorb anymore heat than if it were at a lower pressure since the density does not change (measurably). As I already stated, the exception is IF an engine is putting out so much heat that the flow of coolant cannot absorb the heat sufficiently, in which case it boils. Such a case would likely be rare. And if it were to be occuring, the engine would be running much hotter than is ideal.

Pretty is good! What's wrong with pretty?

Nothing wrong with it. I was merely implying that most people who upgrade their radiator caps don't need to.

Seriously though, but by increasing the opening pressure of the radiator cap's regulator to allow higher radiator pressure it will in effect increase the boiling point of the coolant and reduce bubbles in the coolant system. In turn it improves cooling by circulating liquid and not air, and generally maximizes the cooling performance of the radiator. Everyone knows (at least we do) that air in the coolant passages is not good.

Your statement ASSUMES that coolant is boiling somewhere. But unless the engine gets hot enough to do that, there is no air in the coolant. Therefore, the extra pressure does not provide any help.

Now I should say we are in agreement that the cap should be matched to the radiator being used. I brought up the higher pressure rated cap based on the use of a performance radiator which I could have been a bit more clear; I am basing it on the 300+ crowd which like Papa said it is suggested to upgrade to a racing radiator. Performance radiators are typically rated 22-24 PSI, and professional racing radiators at 29-31 PSI (give or take a few PSI). The highest pressure rated radiator cap that your radiator will accept should always be used. I just wouldn't call it a "band-aid"; it should more be considered a safety net, as once the car overheats by relieving the pressure set by the cap's valve it should be immediately shut down to come to a cool properly. All this brings to light too, it's not a bad idea to upgarde the water pump, to quicken the pace of heat reduction from the engine components through the radiator.

Where are we both saying that a radiator cap should be matched to the radiator's rated pressure? My argument actually implies that a higher pressure cap doesn't provide much benefit for ANY radiator in most cases.

Higher capacity radiators basically do one thing. They increase the dwell time of the coolant so that more heat can be rejected before going back to the engine. Most engines that overheat outside of failures of the cooling systems are because the coolant going back to the engine is not sufficiently cool. Coolant that is at higher temperature cannot absorb as much energy. Thus a feedback loop that causes increasing engine temperature occurs and eventually, the engine overheats. If a larger radiator is added and that causes the engine to be able to run at its normal operating temperature, then the problem was exactly that. Not enough heat rejection occuring at the radiator. And that is not a problem a higher pressure cap can remedy. It will delay the boil-over phase of overheating to a higher temperature, but the temperature of the engine will still be higher than it should be.

Understand that an engine's cooling system's primary purpose is to regulate the engine's temperature. While that encompasses preventing overheating, if your engine is running significantly hotter than it should, then you need to deal with that. A high pressure radiator cap only allows the cooling system to continue to provide functionality while running hotter.

I would agree that it can be a safety net, but if the temperature gets high enough to make a high temperature radiator cap relevant, then I'd probably be pulling into the pit to cool off.

I'll put it this way. Most coolant mixtures boil at about 212 degrees at one atmosphere. The boiling point is typically raised about 3 degrees per psi of pressure. If a radiator cap is rated at 16 psi, then the coolant will boil at about 260 degrees. That's about 80 degrees more than the thermostat's opening temperature. Which is about where the higher pressure cap will show its benefits. I'd be a bit concerned about allowing an engine to run in that range, let alone at any higher temperature. Especially under high loads, and perhaps for extended periods of time.

Performance engines are always going to run higher temperatures due to lots of variables ... it's the nature of the game, thus the reason for the cooling system upgrade(s). I think a good point here is that if one is going to build a higher powered KA engine such as 300hp and up, all of these things need to be seriously considered. BTW, this is a great thread!

For the most part, sure. But there is a lot of overhead built into the engine's internal cooling system. Generally, the biggest limiting factor is the radiator.

I've seen 240s with boiling coolant... Most recently at Carlisle last year.

Sure, but how many were doing so because of faulty cooling systems or not enough heat rejection from the radiator? At the 2002 240 convention, the only incident of overheating I was aware of was a normally aspirated car. Meanwhile my turbo KA was just fine with a stock cooling system. As was a 300+HP KA also running a stock cooling system.

As for the phase diagram, care to elaborate on any point you were trying to make? Noone here is questioning the way the boiling point changes with pressure. My argument is there is no additional heat being carried away by coolant under higher pressures in that of itself...

Sorry if this is getting a little long winded. I'm trying to make sure my argument is understood as it seems to have been misread or misunderstood at least a couple of times.

[WDRacing]

We're taking this thread the wrong way guys. Honestly, I seriously doubt any GAF about the pressure vs temperature argument when they are reading a thread that describes the basic components of a turbo kit.

Of all the issues I've dealt with on all of the vehicles I've ever owned, cooling has never been an issue. Car runs hot, upgrade the radiator...nuff said. The KA24DE doesn't have cooling issues and since that's the motor we're talking about...no sense having a diatribe about rad caps FFS.

This should be a whole new thread. I'll see if I can split it and make a new thread.

[scotty-2-forty]

Sounds good WD ... I think it's all down to interpretation and agreed, it is getting long winded about a simple safety net product that I merely 'suggested' as an add-on to the list. I've not had any cooling issues myself, whether because of the upgrade or not. Good coffee talk though! Thanks C-Kwik; you're the man! Could've used someone like you on my raceteam years ago. Constructive disagreement leads to great results!

Thanks to whomever added my suggestions to the original post (Papa?)!

And I accidently clicked on your avatar WD ... ok-ok, more out of curiosity ... ... thanks, now I'm blind.
Modified by scotty-2-forty at 8:22 AM 3/17/2010

[WDRacing]

And I accidently clicked on your avatar WD ... ok-ok, more out of curiosity ... ... thanks, now I'm blind.

Funny thing is we were trying to code it so that I could actually have a hotlink...lol. Kinda like my title

When it comes to engineering topics, Chano has been my go to guy since he educated me on something like 7 years ago

WD

[scotty-2-forty]

Funny thing is we were trying to code it so that I could actually have a hotlink...lol. Kinda like my title

When it comes to engineering topics, Chano has been my go to guy since he educated me on something like 7 years ago

WD

Obviously a very knowledgeable and opinionated person ... I like him!

[PapaSmurf2k3]

As for the phase diagram, care to elaborate on any point you were trying to make? My argument is there is no additional heat being carried away by coolant under higher pressures in that of itself...

I guess what I was trying to get at was that the higher pressure radiator cap extends the operating temperature of your engine/cooling system. Will you be running hotter than you should be? Yes, but it won't be a catastrophic coolant boiling failure.

We could also throw in Newton's laws of heating and cooling. WHICH, would say your radiator DOES become more efficient (as seen by the slope of the curve) as the difference in temperature increases.

I'll leave it at that to try and keep it short and sweet. But hey, this is why I love the KA-T section, because you can have intelligent discussions like this! We can always split the thread off once the discussion is over with.

Thanks to whomever added my suggestions to the original post (Papa?)!

I left the radiator cap off though... pending discussion.

[scotty-2-forty]

Nice Papa ... love the charts! I also edited my original post re: the 16.8PSI Nismo cap to, "A higher rated PSI radiator cap." I thought brand and rating should be left up to the users cooling application and what type of radiator they are running.
Modified by scotty-2-forty at 1:43 PM 3/17/2010

[PapaSmurf2k3]

Nice Papa ... love the charts!

a picture is worth a thousand words, right?!

[C-Kwik]

I guess what I was trying to get at was that the higher pressure radiator cap extends the operating temperature of your engine/cooling system. Will you be running hotter than you should be? Yes, but it won't be a catastrophic coolant boiling failure.

We could also throw in Newton's laws of heating and cooling. WHICH, would say your radiator DOES become more efficient (as seen by the slope of the curve) as the difference in temperature increases.

Right. And I pretty much stated that there would be an effect the cap would provide if boiling were to actually occur but my point there was that by that time you are already running much hotter than you should. And do bear in mind that my primary argument is that higher pressure coolant, in that of itself, does not carry away heat more efficiently as scotty had stated.

As for the radiator being more efficient, sure, but from a practical and applied sense, no engineer in his right mind is going to use that as an excuse for undersizing a radiator. Especially if the engine ends up damaged from excess heat. Not to mention up until the point a lower pressure coolant boils, the higher pressure coolant will have the same efficiency. Which is pretty much what I've been saying all along. Or in other words, unless you actually get to that point, a higher pressure cap is worthless. If I were running that hot, I'd actually get a bigger radiator and fix the problem. Not figure out how to adapt the motor to an unfavorable condition.

I'll leave it at that to try and keep it short and sweet. But hey, this is why I love the KA-T section, because you can have intelligent discussions like this! We can always split the thread off once the discussion is over with.

Agreed. Despite not having had a KA-T since 2004, I still love the discussions here. Even though I should be working on my Statics Project right now...

[WDRacing]

I was just reading about some water boiling under pressure earlier today. What I got was that increasing the pressure simply raises the boiling point. Which really doesn't accomplish anything because the fluid is still getting hotter...it's just not boiling.

That about accurate? Cause if I summed it up in one paragraph...I win.

[C-Kwik]

I was just reading about some water boiling under pressure earlier today. What I got was that increasing the pressure simply raises the boiling point. Which really doesn't accomplish anything because the fluid is still getting hotter...it's just not boiling.

That about accurate? Cause if I summed it up in one paragraph...I win.

Yep, you are a winner. But I won first:

A higher pressure radiator cap doesn't increase cooling capacity unless a person is boiling the coolant with a standard cap (in which case pockets of vapor will reduce the contact area with the motor).

[PapaSmurf2k3]

Shut up, Brian

But yeah, if you are boiling your fluid, you either have crap fluid in there, or you need a bigger radiator. If you are running the best fluid ever known to man, and have the biggest radiator you can fit under your hood, and have plenty of air going to it, and your engine can sustain a higher temperature than that of the boiling point of the über fluid, then you might want to think about upgrading to a higher pressure radiator cap.

[Chris28]

Only in the KA-T section can I read a thread with a chart of the heat cycle as well as Newton's law of cooling and have it actually relate to the topic. Well done!

As far as the thread's original intent, the first post sums everything up. Very solid information.

[C-Kwik]

Shut up, Brian

But yeah, if you are boiling your fluid, you either have crap fluid in there, or you need a bigger radiator. If you are running the best fluid ever known to man, and have the biggest radiator you can fit under your hood, and have plenty of air going to it, and your engine can sustain a higher temperature than that of the boiling point of the über fluid, then you might want to think about upgrading to a higher pressure radiator cap.

Yep. Not sure about any additive fluids, but a higher concentration of water would improve the coolant mixture's ability to absorb heat as water's specific heat is higher than coolant's. Perhaps only 25% anti-freeze mixture instead of 50/50. My calculations say that a 50% mixture can only absorb just over 90% of the heat energy that 25% coolant can. While 25% coolant can absorb just over 95% of pure water. Or another way to look at it is 50% coolant can only absorb just over 86% of the heat pure water can.

The downside of course is that a lower concentration of antifreeze will lower the boiling point slightly. My speculation is that since motors are supposed to run at a set temperature (+/-), the higher specific heat will be more advantageous as the name of the game is ultimately going to be being able to remove as much heat as possible (net heat). I'm not sure I want to get into the calculations as its a fairly dynamic system as there will be some specific heat with respect to volume as density will be changing with respect to temperature. We can probably pick a few temp points to compare, but one of the more comprehensive sites for the data we would need might have some problems with the data as their chart indicates the same boiling point at 30 degrees and 40 degrees.

Disclaimer - anyone thinking of lowering their coolant concentration should make sure to realize that the freezing point of the mixture will increase so if you live in an area that can see some really low temps, this may not be a good idea.

[PapaSmurf2k3]

ah, so basically, there MAY be some benefit of running pure water+higher pressure rad cap as opposed to 50/50 mix IF you live in an area where you aren't worried about freezing your coolant (or changing your stuff in spring/fall).

[scotty-2-forty]

The problem I see now is that this post has grown into something so technical and lengthy regarding a part that I suggested (not as a requirement), that the average noob reading it will be entirely confused. I can't even keep up with the long windedness of this, and I'm partly to blame. I like pretty ... I'll go with pretty.

[WDRacing]

My biggest issue with running more water then antifreeze is losing the corrosion control aspect of the antifreeze. If you live in AZ or CA and rarely experience freezing you still shouldn't run 100% water because the freeze plugs will corrode and so will the inside of the block.

I would definitely recommend some type of anti rust additive if running a mix other then 50/50 water/antifreeze.

WD

[scotty-2-forty]

My biggest issue with running more water then antifreeze is losing the corrosion control aspect of the antifreeze. If you live in AZ or CA and rarely experience freezing you still shouldn't run 100% water because the freeze plugs will corrode and so will the inside of the block.

I would definitely recommend some type of anti rust additive if running a mix other then 50/50 water/antifreeze.

WD

Well said WD. I've seen people here in south Florida run straight water ...

Thanks for separating the thread WD; and it should be pointed out again that I modified my suggestion from the Nismo cap to simply a higher rated cap, leaving brand and rating up to the user based on their specific application.

I am going to attempt to put all of this into laymen’s terms for the sake of better understanding for those less technical (and that I think no one will read this entire thread, especially a noob who just wants a turn-key racecar for the street ... aw hell I want one!). I get a little confused myself when in deep discussion, so if I repeat myself or disagree on something I actually agree on or mispeak and come back later to correct it ... it's an age thing; deal with it.

Most people will install high pressure radiator caps in an attempt to lower cooling system temps. And yes C-Kwik, some do it just for the looks. Consider too that some cars from the factory are designed to use high pressure caps. However, raising your radiator cap's pressure above factory specs increases your cooling system's maximum operating pressure above factory design parameters. While raising your cooling system's maximum operating pressure does raise your cooling system's boiling point and therefore helps to avoid boil-over, it does not lower your operating temperature prior to boil-over, and simply allows your engine to continue operating at temperatures higher than it is engineered for. Anyone should know that operating your engine at higher than acceptable temperatures can destroy your engine. Okay, some teenage girls don't (no names; personal story; save for another thread). So, consider the following before choosing to replace the cap.

First, there are several possible reasons that an engine might be experiencing higher than normal cooling system temperatures:(1) Engine malfunction or cooling system problem - increasing your cooling system pressure will not correct this problem and will quite possibly add to it. Correct the problem instead of using a higher pressure cap.(2) Engine or body modifications have somewhat altered the performance of the cooling system and/or air flow through the radiator. Again, correct the problem instead of using a higher pressure cap.(3) Engine modifications have increased the HP of the engine thereby creating more horsepower and leading to more heat. In this case, increase the heat dissipation capabilities of your cooling system to match the increase in heat generation. The best way to do this is install an all-aluminum high performance radiator. Simply increasing the radiator cap pressure will not help dissipate additional heat.(4) Your car is being driven in a harsh, high heat environment or is being driven hard for extended periods of time. Again, the best way to solve this problem is install a high performance radiator, because increasing the radiator cap pressure will again not help dissipate heat.

Second, significantly raising your car’s cooling system's operating pressure increases the stress on all the other components of your cooling system. Before increasing your cooling system pressure by replacing your radiator cap with a higher PSI radiator cap, check to make sure your entire cooling system is in good condition and all of the components are capable of handling the higher pressures. Some main components include the radiator itself, the radiator hoses, heater hoses, heater core, water pump, freeze plugs, and all gaskets that come in contact with the cooling system.

Now, although some race cars use high pressure caps, their cooling systems are built to handle these higher pressures by utilizing all-aluminum brazed and welded radiators, steel braided hoses, high performance water pump, high performance gaskets, and eliminating the heater core, etc. High boosting turbo cars and high horsepower street cars usually do something to that effect as well.

Therefore, I still suggest the higher PSI radiator cap for the higher boosting KA engines in our 240's, but knowing well that you should choose a cap with the pressure rating that your particular setup was designed for. Remember, water boils at 212 degrees, and for each pound you raise the system pressure it raises the boiling point 3 degrees - Example: a 1.1 bar (16 pound) cap will have a boiling point of 260 degrees.Oh crap, here comes C-Kwik ... me= ...
Modified by scotty-2-forty at 1:37 PM 3/18/2010

[C-Kwik]

ah, so basically, there MAY be some benefit of running pure water+higher pressure rad cap as opposed to 50/50 mix IF you live in an area where you aren't worried about freezing your coolant (or changing your stuff in spring/fall).

Well, if one were to run pure water, it would still be under the pressure of the radiator cap so the boiling point should still be quite high. I would think that with the additional ability to remove heat, that it would more than offset the need to raise the boiling point further. If I get donw with my Statics project early, maybe I'll try and create an excel spreadsheet with some values we can compare at various temperature points for a couple of concentrations of coolant mixtures.

I do agree with Brian that running pure water would be bad. I probably should have been more explicit, but the reason I compared the 25% and 50% to water was to show that the difference between 0% and 25% was smaller than 25% to 50% coolant mixtures. That is, for reducing the coolant to 25%, you get about 9% more specific heat capacity while the last 25% would only net you about 5%. Which makes sense as the specific heat of the mixture will approach the specific heat of water as the percentage of anti-freeze approaches 0%.

[WDRacing]

Who uses what types of additives and why? I've always used a 50/50 mix of antifreeze/water and a bottle of Prestone anti-rust additive. I always add anti-rust ever since I had some freeze plugs corrode on me.

WD