perplexing cooling probem

[MaineExport]

Well, I need some help troubleshooting a random overheating problem.

Background info:

95 240sx 100,500 miles.Replaced the clutch fan with a dual 10” FAL electricHaven’t replaced the coolant since I’ve owned the car.The electric fans performed perfectly all summer on even the hottest days.

The problem:

About 3 days ago, my car started to heat up while driving home in a snow storm. I assumed it was due to the engine revving a lot as a result of excessive wheel spin most of the way home. But the problem continued right up until today. The car would get up to normal operating temp… then it would start to climb if I came to a stop, or if I accelerated. The only time it would drop back to normal, was while at a fairly constant cruising speed. So it heated up when not in motion (radiator not getting proper airflow?) and while the engine was under stress (thermostat?). Today, on my way to buy a new thermostat and anti-freeze, it stopped acting up. The temp is back to normal no matter how hard I push it. I’ve been driving it all day without a single problem.

I have had thermostat problems with other vehicles, and they either failed open or closed (usually closed). Is it possible that it is failing intermittently? Even if it did fail, the temp would continually rise if closed, or drop too low if open… correct? I’ve had problems with other vehicles with air in the coolant, that never corrected itself. I’ve also had coolant turn into clear liquid with white chunks… and clog up a radiator… but it also didn’t fix itself… and the coolant in this car looks fine.

Well, the next time it acts up (if it does) I could use some advice. What should I look for? Any help would be very much appreciated. I am at a total loss here, none of the symptoms seem to be indicative of one specific problem.

[topless@vabeach]

Yes Thermostats can lock up from time to time. This is the sign to replace it. Also check your coolant with one of the those testers you buy at pep-boys for about $1.99 You might need to add more antifreeze, not just water. The tester will tell you how your coolant is working and what to do to correct it.

[MaineExport]

Thanks topless.

I will definately replace the thermostat and flush and refill the coolant to spec, just for the hell of it.

What baffles me, is that it happens at idle, and under moderate to heavy aceleration. Just cruising, it cools off FAST. It's not like it takes any time to cool down.... literally 3 or 4 seconds after I get to cruising speed it goes from the H down to the middle of the gauge. I would think if the thermostat was failing sporadically it would fail closed or open randomly, not every time I hit the gas or came to a stop.

[1991240xs]

ya ever think maybe the coolant was getting below freezing yesterday and starting to ice up in the radiator?..make sure you have anti freeze in the radiator-

[MaineExport]

ya ever think maybe the coolant was getting below freezing yesterday and starting to ice up in the radiator?..make sure you have anti freeze in the radiator-

I appreciate the thought... and yeah, the coolant is going to be flushed and replaced to make sure. Living in New England my whole life I've become familiar with the need for a heavier ratio of anti-freeze/water. But we've been hitting below freezing temps for over a month, and the problem just started three days ago, so I'm pretty sure it's got to be the thermostat. I'm still just confused as to why it's happening when it happens. The symptoms are just not indicative of a single problem.. but we shall see!

[bruinbear714]

I think its your thermo probe that controls the electric fans... where did you place it? Is it secured down?

[MaineExport]

I think its your thermo probe that controls the electric fans... where did you place it? Is it secured down?

Great idea, but I didn't use the thremostat-kit that was included. I just wired it into the existing wiring for the stock electric fan. It worked fine all summer.

It IS NOT the thermostat. I replaced the thermostat today, and flushed the radiator and block. I replaced the coolant and it still overheats.

I have narrowed the symptoms down to this: It stays at a perfect temp if I am cruising in any gear between 2.5 and 3.5K RPMs. If I let the RPMs drop below 2.5k or go beyond 3.5k it will start to heat up.

Is it possible, that since it depends on RPMs and not speed/coolant/thermostat, that I have a bad impeller or failing water pump?

[MaineExport]

I hate to bump my own thread, but I really need some help here guys! I am going to take it to the garage Monday. I'd like to have a few ideas in mind before I pay them to trouble shoot the problem.

[topless@vabeach]

Can you see the coolant moving when the thermostat opens up? You might have some rust/ corrosion(spelling) blocking your flow. If there is no flow or poor flow this might be a problem but I am just stabbing in the dark.

[PapaSmurf2k3]

I had that same problem this summer. I did the same thing as you, replace the thermo, and coolant, but it still happened every once in a while but then would dissapear for a week or so. Anyway about a week after the last encounter, my water pump blew, and after replacing that it has never happened again. Maybe its some kind of early warning system. who knows. Also, after every refil of coolant, i had quite a few bubbles that would work themselves out on occaision, just keep an eye on the coolant level. hope this works

[MaineExport]

Alright, thanks guys!

K-car... the belt seems to be okay. I've always gone by a general rule of thumb for tension.... it should be easily pushed or pulled about a 1/4 inch up or down. That seems to be the case... would that be about right? I haven't taken the belt off to spin the pump by hand.... what should it feel like anyway? Free spinning or perhaps a little resistance like an alternator?

Papasmurf... how much was that new water pump?

[sullivan864]

i just put one my 90 240- today and it was $35 at autozone

[MaineExport]

i just put one my 90 240- today and it was $35 at autozone

That's comforting!! I can't imagine it would be much more for a DE. I'll check it out tomorrow before I decide to bring it to the garage. Man... $35.... I thought they would be closer to $100.

[PapaSmurf2k3]

My water pump (ka24de) was something like 28 + tax at autozone. it came with the gasket and everything.

[sullivan864]

thats what i'm sayin, i was expecting it to be 100 to 130. i have a honda accord too, and a water pump for that was like 110

[MaineExport]

Well it'll be in the shop in the morning, for less than $40 in parts and an hour labor, I'm feeling better already. I'll know if that was the problem tomorrow. If the a pump doesn't cure it I'm screwed. I'll be left with the radiator, easy to install on my own, but not so cheap.

[MaineExport]

You're not putting it on?

Nice dress.

(In my best Big Gay Al voice)

I hate the way my nails get all dirty.... and my hands get all rough. Ah, it's just a mess!

(back to my normal hairy, filty, and masculine voice)

No, I'm not putting it on... and it does make me a big sissy, I know! Actually, if you knew what my schedule and living conditions are you'd understand. For some reason my landlord doesn't allow people to work on their vehicles in the lot (I found out the hard way!), so I have to drive an hour to my camp. I have school from 8:30am until 1:30pm, then work from 5:00pm until 11:30pm monday through thursday. Then work and band gigs occupy most of my weekend. The only day I can work on my car or truck is Sunday... and this can't wait another week! If it's the radator, I won't be able to afford it until this weekend... but regardless, it's much easier than the water pump (in my experience).

But beyond all my stupid excuses... I'm not into farting around with this crap! Get it fixed and done with!Jerk!

[MaineExport]

[quote=" Lost_To_A_K-Car sit on my *ss for three and a half hours of daylight [/quote]

**cough** HOMEWORK **cough**

and obviously quality time on NICO!!!

I should buy a house.... but I need to be mobile for the next few years. I would need to be in the same place for at least five years, in order to be in a situation in which I wouldn't lose money on the purchase (considering present rates). Trust me, I researched my options. (I'm an accounting major... I get off figuring out what will keep me on top and still meet my needs)

I would much rather do it myself, but time is more of a consideration than money in this case. An hour of shop labor is well worth it at this point. Besides, the owner is a good guy and I owe him some easy money for hooking me up with a couple stickers!!!! (inspection standards in Maine are very harsh for trucks)

[MaineExport]

Originally posted by Lost_To_A_K-Car "]You should feel honored. I'm using my 1000th post to berate you.

I would expect no less!

In Maine. Come on, is it really that hard to count pigs?

I'll have you know, I have only one mother, and she lives in Vermont. No counting involved.

I would much rather do it myself, but I don't want to get my dress all greasy.

I borrowed this dress, otherwise I wouldn't mind.

[MaineExport]

How does this sound:

The diaphragm on the water pump is causing an air pocket, hence the overheating.

Looks like a new pump will do the trick.

[MaineExport]

Okay....so now I have a new water pump, new thermostat, new coolant, and a car that STILL FUC#ING OVERHEATS!!!!!!!!!!!!!!! HELP!!!!!!

:help

[PapaSmurf2k3]

maybe your working out some air bubbles or something. when its overheating, try squeezing the top hose from the radiator to the block, when mine was overheating there was nothing in there but air. (you can tell because it will be really easy to squish and you wont hear any liquid) but maybe its always supposed to be air who the hell knows. maybe you should try kicking it, that always helps.

[bruinbear714]

Quick reality check, did you put the thermostat in the right way? Spring faces the engine. What about bleeding out the air bubbles by opening up the bleeder screw at top of manifold? What about cleaning out the temperature sensors?

[MaineExport]

I'm about to run it into a damn tree and collect some insu.......

I mean, I'm fine.....

Well, I'm fairly sure the rad is fine, because the engine cools rapidly and operates just fine 90% of the time... but then it just overheats.

The tech said (before they replaced the pump) that he thought the head might be cracked or warped, and thus causing the overheating as compression heated up the coolant.

I'm at a total loss here, and now I'm pissed because I'm out some cash! What's a new head going to run me.... enough to make an engine swap worthwhile? I got a rebuilt head for my truck a couple years ago for about $250... but I had it at my friend's garage and it took us about 2 weeks to finish it. I don't have those resources at this point!

[MaineExport]

Originally posted by bruinbear714 "]Quick reality check, did you put the thermostat in the right way?

Yes, thank you.

What about bleeding out the air bubbles by opening up the bleeder screw at top of manifold?

Check! (When we did the thermostat and rad flush) The tech also bled the lines after installing the pump, also once after each test drive he took it on this afternoon.

What about cleaning out the temperature sensors?

Umm, no.... but it's quite obvious that it's too hot on occasion.

Wooo HOoo I'm at 1000 posts now!!! yeah! And I'm about to be out $1000..... everybody I responded to owes me a buck!

[sullivan864]

i would try changing the radiator, they have so many tubes in them that if one of them get bent or clogged it can cause random overheating. this is famous in the refurbished (maybe recored) radiators. always use a new one. anyway sounds like that is what your problem is.

[TX240SX]

You have replaced the thermostat and waterpump. The radiator and fan are the only things left in your cooling system. With it overheating at idle and then cooling at speed it could be either one. The additional air at speed is helping your cooling. If you still have it I would put the stock fan on it and see if it helps. Have you noticed any loss of coolant since the work was done? It could also be a blown head gasket or crack. Have your machanic check the radiator for exhaust gas. A compression check may also help you find a blown head gasket. I would think your mechanic would have tested the radiator for exhaust gas before doing any work. No sense changing out cooling system parts if you know you have a blown head gasket or crack. My bet is you have a blown head gasket. I have read that when you have an aluminum head on an iron block, weak coolant will cause a reaction that will damage the gasket. It is important to change the coolant annually regardless of what is printed on the Anti-freeze container.

[MaineExport]

Thank you TX,

I was not aware that a test existed to check for exhaust gas in the coolant... I will surely consult the garage owner about it. My next step was going to be a compression test to see if it could be a cracked or warped head, or blown gasket.

The overheat now only occurs at speed when the RPMs drop below 2500. It doesn't overheat at idle, or under heavy or moderate acceleration. It gets more and more confusing every day?!!!

[big jon's 240]

This is a new one. Usually cooling problems are the easiest to trouble shoot and fix. Sounds like youve tried just about all the easy fixes. You really sound like you have an internal engine/head problem. Did you cehck for coolant in the oil/ oil in the coolant? (easiest way to check for blown headgasket). Have you looked for other stupid things like bent radiator fins, or too many bugs plastered to it? Sounds lame but it will, in extreme cases, mess things up. ( hey im reaching, ok?) Good luck man, sorry for ya.