Another Overheating Problem

[protek22]

Hello all,

I have read the existing threads on overheating, but none seem to touch
my problem exactly. I would appreciate any input on this:

I do a lot of highway driving, and my 2001 Aurora 3.5 recently began to overheat when traveling above 70 mph. This only occurs when I have started from a cold engine. If I start with the engine warm from previous travel, no overheating occurs above 70. The coolant temperature generally stays between 192-196 deg at these speeds, but now will go up into the red zone, if I hit these speeds soon after a cold start. If I slow down however, the temp gauge will also go down immediately. It usually gets back to normal temperature, at around 50mph. If I maintain 50mph or lower for a while, then the overheating above 70mph goes away. I recently changed the thermostat, but that didn't alleviate the problem.

Thanks in advance,

Protek22

[dsatt12]

A thermostat was the first thing that popped into my head, but as you already did that...

A few things that I can think of, but none of them make much sense with this not occurring after it's all warmed up prior to driving. The easiest is to make sure the system is holding the proper pressure, including the reservoir cap.

Another possiblity is that something bad is making it overheat like head gasket or a cracked engine/oil pump housing/cylinder head or something along those lines. Not good if it is.

The other thing is maybe the engine coolant passages are partly blocked. At lower speeds you have enough coolant flow to keep things going normally, but at higher RPMs it gets too hot. I don't know how you'd go about diagnosing this, but it might be easier to let someone do a power flush and see if it fixes anything (or makes a bunch of leaks...).

You could also have a shop with a top notch scan tool look at all the sensor readings. It could be that one or more of them are all wonky on you but do better when they start out warmed up. They can compare what is being output to expected values and see if it all makes sense. That's a pretty long shot though, as most sensor type things don't really have nearly as much effect once the car is warmed up and at open throttle. Much of it is for emissions purposes when the engine is cold or during stop and go driving.

If you need any other straws grasped at let me know

[protek22]

dsatt12, thanks for the input.
With these uncommon problems, what you need most is ideas. I am going to check on the flush idea first.

[Genopsyde]

I had a similar problem with my 95 cutlass supreme, during acceleration it'd overheat, when I'd let off and coast the temp would drop. problem was the intake gasket. I know it's a different car and everything, but it's definately something to look into.

[protek22]

Genopsyde,

Thanks for the input. Was your problem with the intake manifold gasket? If so, was the overheating the only symptom you experienced?

[Genopsyde]

yes, the intake gasket was a common problem with the GM 3100, i never fixed it tho, I didn't have the time and money so i traded it in for my rora.

[dsatt12]

If you do have the coolant system flushed, remember that it is supposed to get 3 GM seal tabs put back in to keep it from leaking with all the aluminum parts. I've heard they are made of powdered walnut shells.

[protek22]

I was eventually able to fix my problem by replacing the thermostat, and the radiator surge tank cap. No more overheating at any speed, or from any start. I want to thank everyone for their input.

Protek22

[The Rebel]

Originally Posted by protek22

I was eventually able to fix my problem by replacing the thermostat, and the radiator surge tank cap. No more overheating at any speed, or from any start. I want to thank everyone for their input.

Protek22

So, Proteck22, you said in an eariler post that you change the thermostat. Was this the second thermostat you changed along with the one-time change of the radiator surge tank cap?

[protek22]

No actually after the first thermostat change, I still had some overheating. I then changed the surge tank cap and this resolved the issue. I think both changes were needed however.

[zephram22]

Originally Posted by protek22

No actually after the first thermostat change, I still had some overheating. I then changed the surge tank cap and this resolved the issue. I think both changes were needed however.

Thanks. I'm gonna try that with my '02 3.5 since I'm having the same problem.

[zephram22]

Originally Posted by protek22

I was eventually able to fix my problem by replacing the thermostat, and the radiator surge tank cap. No more overheating at any speed, or from any start. I want to thank everyone for their input.

Protek22

Protek22,

How many miles did your care have on it when you replaced the thermostat. Did the problem start slow and become much worse. (I.e., did it start by overheating just a little, but after a time happen during almost every trip?) I'm starting to think my thermostat is going bad as well. I have noticed that it is taking much longer for the car to warm up during the past few days.

[tedcopeland]

Do the 2nd generations have 2 cooling fans? If so, can you pull over as soon as it gets hot and take a peak in to see if they are both on. I'd be leaning towards a sensor of some type where it does seem to correct itself. Also, there is a leak detection device that you can buy for about $35. It is a rubber grommet that fits in place of the radiator cap. That is attached to a plastic tube that goes in the top of a test tube that is sealed with a rubber cap. After the tube passes thru the seal, it goes down to the bottom of the test tube. There is a blue fluid that you pour into the test tube and reseal. The plastic tube has a pump like device which name escapes me, that is like the old style blood pressure straps. You squeeze the pump and it sucks air from the overflow bottle. DO NOT SUCK COOLANT! The blue fluid will turn yellow. I've seen it tutrn yellow after one or two pumps and I've seen it take as long a minute (directions say up to two minutes) of pumping. This tells you that you have exhaust gases getting into your cooling system. If it stays blue, look elswhere.

[zephram22]

Originally Posted by tedcopeland

Do the 2nd generations have 2 cooling fans? If so, can you pull over as soon as it gets hot and take a peak in to see if they are both on. I'd be leaning towards a sensor of some type where it does seem to correct itself. Also, there is a leak detection device that you can buy for about $35. It is a rubber grommet that fits in place of the radiator cap. That is attached to a plastic tube that goes in the top of a test tube that is sealed with a rubber cap. After the tube passes thru the seal, it goes down to the bottom of the test tube. There is a blue fluid that you pour into the test tube and reseal. The plastic tube has a pump like device which name escapes me, that is like the old style blood pressure straps. You squeeze the pump and it sucks air from the overflow bottle. DO NOT SUCK COOLANT! The blue fluid will turn yellow. I've seen it tutrn yellow after one or two pumps and I've seen it take as long a minute (directions say up to two minutes) of pumping. This tells you that you have exhaust gases getting into your cooling system. If it stays blue, look elswhere.

Yes, 2nd gens have 2 fans. I'm having the same overheating problem. Fans were running. But, the thermostat was on its way out. The car was always running hot, but the damn thing didn't realize it half the time.

[zephram22]

I would check the fans to make sure they are coming on. Also, you can remove any debris and such from the radiator fins with a stiff-bristled brush. Make sure the coolant is still ok, there is enough of it, and that it is the proper mixture. Too much anti-freeze and not enough water will not cool effectively. Also, make sure that lip is still on the front of the car as it directs air into the radiator. My bet would be the fans, though, if it only runs hot while you are moving slow. There's also always the possibility that the temp sender is old and is no longer accurate.