My 1991 944S2 ran with temperature needle just above the third mark this morning on my drive work work, out of the normal running range. It was around 72 degrees with high humidity, the AC was running, and the car wasn't driven hard at all. If that kind of driving makes the engine run hot, I wonder what it will do when it's really hot outside.

What would you recommend checking out first? The car has 147,000 miles on it, so could the temperature sensors that allow coolant to flow to the radiator going bad? The coolant was changed two years ago by a mechanic, but not flushed. Would you change that first? (I heard that's a lot of work on the 944S2.)

If this was my old Honda, I'd follow these steps: Verify the fan was turning on, then bleed the radiator, then replace the temperature sensors, and finally flush the radiator. Would this kind of procedure work on a 944S2?

thanks,
Bryan

 

Hi Bryan,

Off the top of my head I'm not sure if that is hot, if that is what or where you drivers handbook say's it IS hot then fine.

Let us assume it is.

ok a few things:

1>
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On Porsches overheating problems can be separated into categories:

1 Insufficient Air Flow - cooling fans ???
2 Insufficient Coolant Flow
3 Coolant Leaks
4 Insufficient Cooling Capacity
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2>
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Using the A/C during periods of extreme engine load (climbing hills/towing/hard or fast driving) may exceed the capacity of the cooling system.

The A/C system actually places two additional loads on the cooling system:

A/C heat removal in the condenser (preheats incoming air before it reaches the radiator).
Increased engine load from operating the compressor.

When I had a problem on my Capri, I used to loose excess heat by switching on the heater, this utilised the inside heater radiator as anm extra cooling system, a bit rough in summer !
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Assuming your still concerned heres how to initial test the cooling system
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FROM COLD

1> Remove the radiator cap/expansion tank cap and check the coolant level, refill as necessary.
2> Pressurize the cooling system and check for leaks

3> Inspect the radiator, check the cooling fins are not blocked with debris. Oil is not contaminated with coolant. Check bottom side of oil filler cap, this is where coolant contamination often accumulates first.
Check oil with dip stick, if contaminated with coolant or water itwill have a creamy, light brown color, often called "Mayonaise" !

4> Check that the coolant temperature switches and sensors are connected properly. That all
radiator hoses are not pinched.
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Holla back if you've still got a problem

regards

Adrian

 

I replaced the tstat (a real bitch if the water pump remains installed) and the fan switch and this fixed my overheat problem. But at your mileage, you might look at a bad water pump.

 

Thanks for the tips. Last night I cleaned the coolant overflow container, or rather tried to clean it. After around five flushes I rinsed it well and put it back, filling with distilled water. It's much cleaner now, but I still need to find a solvent that will clean the insides better.

This morning it was 60 degrees outside, the AC was off, and the needle went fairly quickly to the third mark and sat there. I drove for maybe 15 minutes, then when I got to some stoplights the needle dropped to the middle range where it normally runs.

I'll keep investigating. Maybe it was somewhat low on antifreeze or the overflow container was too blocked with gunk. According to the manual, since I added more than a liter of coolant I now need to bleed the system. That's tonight's project. (It gets dark too early this part of the year!)

Bryan

 

[quote]Originally posted by Bryan Welch:
[qb]Thanks for the tips. Last night I cleaned the coolant overflow container, or rather tried to clean it. After around five flushes I rinsed it well and put it back, filling with distilled water. It's much cleaner now, but I still need to find a solvent that will clean the insides better.[/b]

ok, there are some products called rad flush which are fine as long as they are used exactly as directed.

I wouldnt use Distilled water, which I believe is the same as de-ionised water, as it's quite aggressive, as opoosed to ordinary water. That really shud be sufficient.

After flushing forward, try reverse flushing as well, that is the opposite way the water runs, could also try removing rad pipes and flushing the radiator free, normal and reverse flow.

Dont attempt to use any other aggresive chemicals, and ALWAY'S re-fill withcoprrect mixture of anti-freeze, as this will stop engine damage and corrosion.


This morning it was 60 degrees outside, the AC was off, and the needle went fairly quickly to the third mark and sat there. I drove for maybe 15 minutes, then when I got to some stoplights the needle dropped to the middle range where it normally runs.

are both fans coming on ????

I'll keep investigating. Maybe it was somewhat low on antifreeze or the overflow container was too blocked with gunk. According to the manual, since I added more than a liter of coolant I now need to bleed the system. That's tonight's project. (It gets dark too early this part of the year!)

good luck

Bryan[/b]<hr></blockquote>

 

Ok,
Are both fans turning on? If only the low-speed fan is working, your car is going to run hotter than normal. If both fans are working, the next step is to check the coolant system. If your coolant is staying at the right level, you may try changing the thermostat...which is not too heavy of a job to do yourself. Also, when you refill the system, you need to also bleed it (burp it) by unscrewing the bleeder valve (its a bolt on the top of the motor, but don't unscrew it too much or the pressure will shoot that thing up and away....the bolt has a hole in it to let fluid spray out).
-Robert D.

 

<a href="http://www.tech-session.com/Paragon/Tech/944_coolant_flush.htm" target="_blank">http://www.tech-session.com/Paragon/Tech/944_coolant_flush.htm</a>

 

Testing the car tonight, I started the car, let it warm up to running temperature, then held the RPMs at 2500 to warm it up further. The AC was left off. The temperature rose until it just passed the third mark, just above the 'normal range', and the fans both turned on at high speed. They stayed on until the needle dropped to the middle of the 'normal range'. When I turned the engine off, the fans kept running for a bit.

After letting the car cool off, I ran it with the AC on. As soon as I turned on the AC, the fans both started running at low speed. The temperature never got to the third mark, so the fans never switched to high speed. When I turned the engine off, the fans stopped running.

I'm thinking the problem is with the temperature switch that turns on the fans at low speed. Is this in the radiator? I heard there are two temperature switches on the engine. Could this also be a thermostat problem?

A previous post mentioned checking the wiring and resistors in front of the windshield. That's tomorrow evening's project.

 

I'm not clear on the exact function of the thermoswitch (the only one that I know of), but my fans were never working except when the compressor was on, I replaced it, and they're fixed. The thermoswitch is like halfway down (from hood to bellypan direction) the driver's side of the radiator. It will take some reaching and a 30mm deep socket, but otherwise a really easy job. Maybe $20 part.

 

[quote]Originally posted by Bryan Welch:
<strong>
This morning it was 60 degrees outside, the AC was off, and the needle went fairly quickly to the third mark and sat there. I drove for maybe 15 minutes, then when I got to some stoplights the needle dropped to the middle range where it normally runs.</strong><hr></blockquote>

Bryan, when last was the timing belt retensioned ? I believe you mentioned that it has been 2 years since the coolant was replace. If the belt has not been looked at since than it maybe as simple as getting the belt retensioned and the water pump checked out. The timing belt drives the water pump. If the belt is loose it may be slipping on the pump or slipping on a bad pump.


[quote]Originally posted by Bryan Welch:
<strong>I started the car, let it warm up to running temperature, then held the RPMs at 2500 to warm it up further. The AC was left off. The temperature rose until it just passed the third mark, just above the 'normal range', and the fans both turned on at high speed. They stayed on until the needle dropped to the middle of the 'normal range'. When I turned the engine off, the fans kept running for a bit.

After letting the car cool off, I ran it with the AC on. As soon as I turned on the AC, the fans both started running at low speed. The temperature never got to the third mark, so the fans never switched to high speed. When I turned the engine off, the fans stopped running.

I'm thinking the problem is with the temperature switch that turns on the fans at low speed. Is this in the radiator? I heard there are two temperature switches on the engine. Could this also be a thermostat problem?
</strong><hr></blockquote>

The fans should have turned on at low speed when the needle reached halfway between the 2nd and the 3rd marks. Thats the first switch in the fan thermo switch kicking in, when the needle reaches the 3rd mark the fans should go on at high speed when the 2nd switch kicks in. It is normal for the fans to run all the time when the AC is running.

 

[quote]Originally posted by Mark Lue:
<strong>

The fans should have turned on at low speed when the needle reached halfway between the 2nd and the 3rd marks. Thats the first switch in the fan thermo switch kicking in, when the needle reaches the 3rd mark the fans should go on at high speed when the 2nd switch kicks in. It is normal for the fans to run all the time when the AC is running.

I would replace the thermofan switch if the low speed fan is not comming on when the needle passes the half way mark between the 2nd and 3rd marks.
</strong><hr></blockquote>