Weird running hot issue

[tollboothwilley]

About 2 months ago when I came here to Phoenix my car was running hot every now and again when I would start driving after sitting at a stop light. I think that running a little warm like that put extra strain on my radiator and caused it to leak due to the extra built up pressure.

I replaced my radiator with a KOYO radiator and also the radiator cap.

After I replaced my radiator I have had no problems until today. The temperatures here in PHX were much lower than normal for june, we were mostly in the 90's. The last few days have heated up to 110* or so though and I have noticed the temp gauge climb 2 times today.

It only happens with the AC on, after I have already been driving for a good 25-30 min, and after I have been stopped at a traffic signal for a minute or two. The needle only moves about 2 notches. I turn off the AC and it went back down to normal. Turn the AC on and it didn't duplicate the problem again for another 10 min. Like I said, it only happened twice.

So, I have new radiator, obviously have changed out the coolant (even added some Redline Water Wetter). I changed out the T-stat a couple months ago. Coolant level was to the MAX line yesterday when I checked fluids.

What do you think is the issue???

[johnparkyourcar]

I dunno what the problem might be but you should take care of that asap before it leads to other potential problems. I wish I can help you out, hopefully the techs here can help you out...

[smockers83]

So it's not leaking anymore, correct?

Are your fans working?

[biggie]

Fans are my first thought as well.

[tollboothwilley]

Fans are both working. I'm wondering if I need bigger fans than double 12" now.

Aside from the 2 times that it happened, it didnt happen any more. Including a lot of driving around a neighborhood in the same heat (low speeds).

[tollboothwilley]

The fact that my original radiator died may be irrelevant as well since it had a good 140K miles on it. It was probably waiting for a reason to retire.

[zozoka1212]

110 is frickin hot. You guys really close to hell. LOL Do you know if your thermostat works well? Sound like either that or your fan. But you said the fans are working so it would lead to the thermostat. Also if you think about even with the fan on and the car isn't moving that not much of a help. I am not an expert tho.

Just see this way,traditional oven vs convetional oven. Conventional oven cooks thing lot faster with same temperature. Only diffrence is the fan running.

I would go with aftermarket thermostat if I were you. It is good performance wise anyways. It openes a little earlier than the OEM.

Only other thing I can think of is maybe you have a little engineinterior leak and maybe the exhaust heats it up. It could be just really minimal but enough to trigger it when it is still stand but when it moves it has enough to cool it down. If it was the headgasket it would be more and more so it might be something else. Hope not a little crack in the engine.

Just an idea. Could be way off. Well possibly. LOL

The tech guys will be here soon to give a lot more help. A real one.

[tollboothwilley]

Yes, I agree 110 is really hot. What is weird is that I haven't had any other heating issues. If there was a crack in the block or something I would expect to see more issues...especially with coolant disappearing, lack of performance...something.

[pfarmer]

About 2 months ago when I came here to Phoenix my car was running hot every now and again when I would start driving after sitting at a stop light. I think that running a little warm like that put extra strain on my radiator and caused it to leak due to the extra built up pressure.

I replaced my radiator with a KOYO radiator and also the radiator cap.

After I replaced my radiator I have had no problems until today. The temperatures here in PHX were much lower than normal for june, we were mostly in the 90's. The last few days have heated up to 110* or so though and I have noticed the temp gauge climb 2 times today.

It only happens with the AC on, after I have already been driving for a good 25-30 min, and after I have been stopped at a traffic signal for a minute or two. The needle only moves about 2 notches. I turn off the AC and it went back down to normal. Turn the AC on and it didn't duplicate the problem again for another 10 min. Like I said, it only happened twice.

So, I have new radiator, obviously have changed out the coolant (even added some Redline Water Wetter). I changed out the T-stat a couple months ago. Coolant level was to the MAX line yesterday when I checked fluids.

What do you think is the issue???

Just because you gain heat doesn't mean you gain a lot of pressure. I recently (yesterday) purchased a ScanGaugeII. This connects into your OBDII port and can report serveral items to you in real time, one of which is your temperature in digital form. I have mine mounted on the dash just to the left of the pod and a quarter inch from the windshield. Any scan reader for real time will work however.

Now get yourself a steam table off the net and compare your true temperature to what is possible in the way of your pressure. If you fall below the saturated temperature at the rated pressure you should not have any problems due to pressure, at least from creating steam. Air could be a different factor if you are sucking it in some place like the water pump seal.

You mentioned that you are at the max level on your coolant, was this a cold reading? Not sure on your car but is this a normal level cold for yours and what is it when hot? If you gain here anymore than a minimal amount and you are not running hot then suspect either getting air into the system or something like engine gasses. Remember that air into the system can raise engine temperature while the water temperature can actually be reduced due to blanketing.

Perry

[Sentientbydesign]

It's possible that the t-stat was designed for lower ambient temperatures and because it opens up at a given temperature, the ambient air isn't cool enough to cool down your radiator fluid fast enough which allows the temperature to spike.

Also, be sure your water pump is working correctly and that the fans are coming on when they're supposed to.

I believe the dual fan design allows for one fan to come on when coolant temperatures hit a certain threshold and the other fan is on when ever the A/C is on.

Also, you have a very high mileage G. Is is possible that you need a good coolant flush?

[telcoman]

I replaced my radiator with a KOYO radiator and also the radiator cap.

What do you think is the issue???

A few things come to my mind but check this out

http://www.nicoclub.com/FSM/G35/Sedan/2003/co.pdf

After I replaced my radiator I have had no problems until today. The temperatures here in PHX were much lower than normal for june, we were mostly in the 90's. The last few days have heated up to 110* or so though and I have noticed the temp gauge climb 2 times today.

It only happens with the AC on, after I have already been driving for a good 25-30 min, and after I have been stopped at a traffic signal for a minute or two. The needle only moves about 2 notches. I turn off the AC and it went back down to normal. Turn the AC on and it didn't duplicate the problem again for another 10 min. Like I said, it only happened twice.

So, I have new radiator, obviously have changed out the coolant (even added some Redline Water Wetter). I changed out the T-stat a couple months ago. Coolant level was to the MAX line yesterday when I checked fluids.

What do you think is the issue???

How is the water pump?

How do the specs of the radiator compare with the OEM radiator?

Same for the thermostat and radiator cap?

Also try using the factory recommended coolant.

The FSM CO section has additional items to check

Good luck

Telcoman


Modified by telcoman at 3:04 PM 6/25/2009

[tollboothwilley]

I recently flushed out the fluid when i replaced the T-stat (about 2 months ago). And then I did it again when I replaced the radiator.

The T-stat that I put in is a 350Z version where it opens at 170* instead of 180*. It should allow it to stay a little cooler if anything, right?

[tollboothwilley]

A few things come to my mind but check tis out

How do the specs of the radiator compare with the OEM radiator?

Same for the thermostat and radiator cap.

Telcoman

The radiator is a better brand with slightly better cooling. Capacity is about the same. The radiator cap is stock replacement.

[biggie]

Just checking, but you replaced the T-stat, then later had to drain again and replace rad?

If so its possible that the T-stat is sticking some. I always follow the rule if draining the coolant then replace the T-stat as well. For some reason it can (and has on multiple occasions) mess up the T-stat when it is drained and reused.

[Tampa G35 Sedan 6MT]

I recently flushed out the fluid when i replaced the T-stat (about 2 months ago). And then I did it again when I replaced the radiator.

The T-stat that I put in is a 350Z version where it opens at 170* instead of 180*. It should allow it to stay a little cooler if anything, right?

Wrong... Had similar problem with my jeep.

When you have a 170* and not 180* the T-stat opens sooner v. later. What happens is that because it opens sooner the fluid in the radiator doesn't have enough time to cool properly. This causes the fluid to come back into the engine at a higher temp. Then the T stat has to open sooner again and the coolant never can get to the proper temp.

The entire cooling system is designed around a certain temp and that is why you should always put the same temp t stat in the car. Change it back and see if it works.

DJ

[smockers83]

The reason I say fans or even the cooling ability of your radiator is because you say it moves up when you stop. When you stop, there's no air flowing past the radiator. That's what the fans are for and if those are working, then either what Tampa said or the ability of the radiator. Could also be an air bubble or air leak in the system.

[tollboothwilley]

Wrong... Had similar problem with my jeep.

When you have a 170* and not 180* the T-stat opens sooner v. later. What happens is that because it opens sooner the fluid in the radiator doesn't have enough time to cool properly. This causes the fluid to come back into the engine at a higher temp. Then the T stat has to open sooner again and the coolant never can get to the proper temp.

The entire cooling system is designed around a certain temp and that is why you should always put the same temp t stat in the car. Change it back and see if it works.

DJ

Hrmmm.. Why do people that go FI use a 154* NISMO thermostat?

I thought that the t-stat stays pretty much open all the time after the engine has been running at operating temp for a little while. In which case, having the t-stat stay open longer would just allow for a constant lower temperature.

[pfarmer]

I recently flushed out the fluid when i replaced the T-stat (about 2 months ago). And then I did it again when I replaced the radiator.

The T-stat that I put in is a 350Z version where it opens at 170* instead of 180*. It should allow it to stay a little cooler if anything, right?

Just for a reference. My 2008 xs in 71 degree weather was running at about 193 degrees. I believe either thermostat would most likely be fully open at this point based on how most thermostats work. I think at the temperature my car was running at that the thermostat was most likely fully open if the operating range is what I suspect it to be.

If you are running one that opens at 170 degrees then it most likely is fully open even earlier. This can affect things in a negative way such as fuel economy and engine wear and tear depending on how the car is used. But once fully open the rating will make little difference if everything else is equal such as flow characteristics through the thermostat.

In your case your ambient was much hotter, the thermostat is functioning properly then is basically out of the picture for cooling purposes. At this point your fans and water flow via the pump become the controlling factor, the design of the radiator is a constant.

In the case of your fans make sure they are in fact spinning in the correct direction (both of them). I have seen a couple of electrics wired opposite. Most likely this is not the case and what you are seeing at 110 degrees is most likely normal for the driving condition.

Perry

[Tampa G35 Sedan 6MT]

Trust me on this one... If it opens sooner the air never gets a chance to cool the fluid. Even with the fans running, which i assume they are, they never get the chance to cool the fluid because it is constantly moving..

I don't ever think the t stat is open always.

In my jeep when the motor is cool I can watch the thing get hot and right to half way and when it hits that point it opens and the cold coolant flows into the motor and then I see the temp drop. Our car the Computer manages all this electronically.

Note: when you are driving the higher rpm's turn the water pump. That is why when you are at a stand still the water pump is also pumping very little water. When the fans are working properly and you take off again from a stop, the temp goes back to normal because the radiator has cooled the fluid with the help of the fans and the t stat has opened because the engine temp has reached the point at which it opens.

If the T stat opens sooner and you are at a stop it will just circulate hot coolant.

[tollboothwilley]

In the case of your fans make sure they are in fact spinning in the correct direction (both of them). I have seen a couple of electrics wired opposite. Most likely this is not the case and what you are seeing at 110 degrees is most likely normal for the driving condition.

Perry

Great, thats the logic that I followed and what made sense to me. I should double check the fans just to make sure they are both spinning in right direction. It would be counter intuitive to have one pulling while the other is trying to push. In which case if the one fan is pushing it would make sense that if it was running a couple degrees warmer at a stop and the high side fan kicked on that it would run hotter.

However...I dont see the temp rise up while I'm at a stop. Its AFTER I start moving and have been stopped for a few min in the high heat.

[Tampa G35 Sedan 6MT]

when you are say driving 70mph on the high way what happens is that the coolant gets warm in the motor to a certain temp and then the t stat opens. the high rpms make for a fast change in coolant from radiator to engine, then it closes and the hot coolant cools as the cool coolant warms.

This might happen 20-30 times in a min but it never stays open.

the water pumps in our cars could pump probably 5,000 gallons an hour at 3k rpms if the t stat stayed open and i don't even think it holds over 2 gallons of coolant.

DJ

[Tampa G35 Sedan 6MT]

Great, thats the logic that I followed and what made sense to me. I should double check the fans just to make sure they are both spinning in right direction. It would be counter intuitive to have one pulling while the other is trying to push. In which case if the one fan is pushing it would make sense that if it was running a couple degrees warmer at a stop and the high side fan kicked on that it would run hotter.

However...I dont see the temp rise up while I'm at a stop. Its AFTER I start moving and have been stopped for a few min in the high heat.

This is because the t stat is open and your new radiator is probably more efficient than the old one. So it is just holding the temp longer because it carries more fluid than the old one.

[tollboothwilley]

Its not a higher capacity radiator. Just a better brand and new.

The coolant system holds approx 3 gal.

Operating temp in the engine should be around 190-204* for optimal performance. I would think that the T-stat is fully open the entire time.

[Tampa G35 Sedan 6MT]

I could be wrong, but this is the same problem I had when I put a 180* t stat in my jeep. It calls for 196*. Once I changed it back it hasn't given me a problem since.

Keep me posted.

DJ

[tollboothwilley]

Hrmmm... Thanks for your input DJ

I might have to try that, even though I dont want to change the thermostat again. I feel like i've bought 15 bottles of coolant in the past 2 months. That shiz's expensive.

[Sentientbydesign]

Heat exchange should be about the same if you were constantly cooling the coolant or cycling it.

If you think about it, all that's happening is heat transfer.

Block->coolant ->radiator->ambient air

If the radiator/fan combo lowers the coolant by X number of Joules per minute. What difference does it make, if it's lowering the entire 3 gallons or 1 gallon which will mix with the other 2 gallons when the t-stat opens?

I'm not so much arguing here as I am curious if someone has some thermodynamics information to shed on this.

[Tampa G35 Sedan 6MT]

All I know is that it worked in my Jeep and I had a mechanic tell me that. He had been working on jeeps for 35 years

DJ

[pfarmer]

Great, thats the logic that I followed and what made sense to me. I should double check the fans just to make sure they are both spinning in right direction. It would be counter intuitive to have one pulling while the other is trying to push. In which case if the one fan is pushing it would make sense that if it was running a couple degrees warmer at a stop and the high side fan kicked on that it would run hotter.

However...I dont see the temp rise up while I'm at a stop. Its AFTER I start moving and have been stopped for a few min in the high heat.

For the benefit of some others. There are a couple of variations of thermostats. Some work by metals that are bonded together that expand at different rates. At a design temperature this causes the thermostat to be open and pass water. Another style that is very common is one filled with a special wax. At at a design temperature the wax melts which opens the thermostat. Both of these sit in the water stream and pick up the hot coolant from the engine. At this design temperature the thermostat will open which passes water flow through the radiator. A couple of variations here as well. On some systems this will essentially pass water to both the engine and radiator side at the same time, on others it means passing all the water through the radiator before it reenters the engine.

For a short period you can have the thermostat cycle when cooler water which is sitting in the radiator first enters the water stream to the engine and returns at a low enough temperature to reclose the thermostat. In some designs a small amount of water is bypassed around the thermostat to allow the radiator to come up to temperature as well prior to the thermostat opening. There is a bandwidth where the thermostat is partially open. Many will test their thermostats in a pot of water measuring when it first starts to open until the fully open point. Once above the fully open temperature the thermostat is then fully open and as long as the coolant temperature is above this point the thermostat is effectively out of the picture as far as controlling temperature.

Basically the lower temperature rating of a thermostat means it will open earlier and in many if not most cases will also be fully open earlier as well.

So my belief is in your situation the thermostat is most likely fully open all the time after your engine reaches operating temperature. For the benefit of the engine and economy you want the engine to reach normal operating temperature as soon as possible as long as you don't exceed the design temperature rate of change of the metals and design differential expansion rates between various components. On newer cars this occurs much faster then older ones.

If you have an accurate water temp reading I think you will see that the running water temp is above the fully open position of your thermostat if you were to test it in this way. Your fans will most likely just drive it down close to the normal operating temperature which I think you can see if you watch the point they come on and shut off. They will have their own bandwidth to keep them from cycling on and off continuously. On some sophisticated systems there may have some control circuit that will measure temperature change over time.

As far as pressure goes many will put on a higher pressure cap. If your old cap is not relieving the new cap will do nothing as far as the system is concerned. A 50-50 water to antifreeze mix will allow your system to run at around 225 degrees, add another 40 degrees or so at 15 lbs. and for most this means they will not exceed most stock radiator cap set points.

My experience has been with a pure water mixture you will see very little level change in a closed system until close to about 160-170 degrees. Many older trucks use to run at around 180-190 degrees and sported a 5-6 lbs. radiator cap. With newer systems you may well be running in this area but with the higher possible pressures you have a much higher safety margin before the boiling point is reached.

As a reference on my 2008 it appears that the temp gauge starts to move off the bottom at about 118 degrees and at the normal running temperature of about 190 degrees the needle sits at just under the midway point (about 1-2 ticks).

Good luck if there is actually a problem.

Perry

[pfarmer]

Its not a higher capacity radiator. Just a better brand and new.

The coolant system holds approx 3 gal.

Operating temp in the engine should be around 190-204* for optimal performance. I would think that the T-stat is fully open the entire time.

If running a 170 degree thermostat most likely true. Typically with a 190 thermostat it may well be fully open between 195-200 degrees. A 180 degree thermostat may be fully open at about 190 degrees. So it stands to reason that a 170 degree thermostat will follow the same basic rules with slight differences.

One topic brought up is RETENTION TIME. Basically if coolant flows through the engine block too quickly it may not have enough retention time to pick up the necessary heat. The same can occur in a radiator depending on design. Some industrial heat exhangers will have orifices to control not only the rate of flow through the device but also through individual tubes in the heat exchanger. In a radiator, especially newer ones, you will find features that prevent this from occurring by causing a design turbulance. This does a couple of things, one is to control total flow, the other is to ensure that stratification is not occurring, that is that the coolant in contact with the tubes doesn't prevent other coolant from being in contact with the tubes. Think of this like a large pipe. Flow in a large pipe can have fluid that stays in contact with the sides of the pipe follow this path through the length of the pipe while fluid in the center stays in the center.

You mentioned that you 'flushed out' the system. How was this done? Keep in mind that the thinnest of insulation from a film on the parts being cooled can drastically affect the effectiveness of the cooling system. This is sometimes referred to as a 'skin'. Sometimes a back flush will be enough, at other times it may be necessary to chemically do this but this is possibly something to leave to the shop who has a good idea about what works and what can actually harm the system.

Perry

[pfarmer]

Heat exchange should be about the same if you were constantly cooling the coolant or cycling it.

If you think about it, all that's happening is heat transfer.

Block->coolant ->radiator->ambient air

If the radiator/fan combo lowers the coolant by X number of Joules per minute. What difference does it make, if it's lowering the entire 3 gallons or 1 gallon which will mix with the other 2 gallons when the t-stat opens?

I'm not so much arguing here as I am curious if someone has some thermodynamics information to shed on this.

The rate of heat exchange will be based on temperature differential and the ability of the heat exhanger (radiator) to maintain this. Factors such as retention time also play a part. What appears to being confused here is the flow path with the thermostat closed versus open. It makes sense to consider that flow will always be through the engine and if you look at most auto thermostats it opens when hot and closes when cold.

You have the flow path basially correct. There may be some variations on where in the path the water pump enters into the picture.

So basically

1. Block>Coolant>Water Pump>Block............... when cold2. On some systems Block>Coolant>Water Pump>Radiator>Block .............when hot.

3. On some other systems you may see Block>Coolant>Water Pump>Radiator and Block........ when hot

4. And on still others Block>Coolant>Radiator>Water Pump>Block ....... when hot.

From what I see we are number 1 and number 3.

Perry