944 Overheating, PLEASE HELP?

[twerp129]

OK, my 83 944 is overheating, but, it isn't the radiator or the thermostat, and the water pump doesnt show any signs of a problem, (No Squelling, Leaking, Etc.) The problem occured on a long drive where my trip odometer puked also, any advice on what to do would be greatly appreciated? Could it be the gauge, or if its the water pump how can I tell? HELP!

[Slam]

Need more info. How do you know it's not the rad or thermostat? Are the cooling fans working? When the car heats up, can you filp on the AC switch and kick in the fans? When you do, does the temp drop? When you bridge the contacts on the thermo switch (top driver's side corner of the rad), do the fans kick in? Is your cooling system pressurising too much when the car heats up? Even timing belt tension can affect temp. Was your trip through the mountains? How's the fuse?

Don't know if I've helped or not, but you may have something to follow to track down your culprit.

HTH

[twerp129]

thermostat - tested by mechanic
radiator - ran water through it and came out flowing evenly, thus indicating no clogs.
I will check the fans
Also, was told to check the water pump, by running the car and clamping a hose with your hand and then releasing and feeling for a surge of coolant, will, try this also.
And what is this overpressurising the system, because i recently added coolant and it was a little above the max but figured it was OK.

Thanks for all the help!

[Tishabet]

Originally posted by twerp129
thermostat - tested by mechanic

So you've already involved a mechanic and they can't figure it out?
In any case, Clarks-garage.com has conveniently listed all the possible causes of your problem:
-If the car runs hot and the radiator is cool, the thermostat sticking is a possible cause.
-The coolant system may not be properly vented.
-There may be a blockage in the hoses or radiator.
-The cooling fans may not be operating properly. This can be caused by the fan relays, fuses, or the thermofan switch. One fan is for normal operation. It should run in warm weather if you are sitting in traffic. The other fan will normally run if the A/C is on.
-An incorrect water/antifreeze ratio can cause the car to overheat. For most climates, a 50/50 mixture is best for all weather conditions.
-The head gasket may be leaking.
-The water pump may be bad. Rebuilt water pumps have been known to have the pulley slip on the shaft. Others have had the pump impeller separate from the shaft.
-The temperature sensor or gauge may be faulty.
-The radiator cap may be faulty. If you do not have a coolant pressure tester and suspect the radiator cap, most major auto parts stores can test it for you.

[twerp129]

Well I replaced the thermostat and it is still doing it, but, what happens is it idles fine past the third hash mark hits the solid yellow bar and then temp comes back down, is this normal?

[Tishabet]

No, that's not normal. When did you replace the thermostat? did you run the clarks-garage checklist?

[Cebu]

Also, be aware that a partially clogged catalytic converter will cause high engine temp and failure of a smog test.

[twerp129]

Ive noticed one thing, when the engine rpms are up it cools faster. And why would the fan be a poblem, when ideally it shouldn't come on until the solid yellow line?

Also, if it is the Water pump shouldn't it make a noise, or something, I squeeze the outlet of the water pump and I feel some flow, but, I have nothing to compare it to too know what is normal?

[Tishabet]

Instead of feeling the hose, feel the radiator...is it hot?
increase in RPMs making the car cool faster says to me that your pump (most likely the impeller) is possibly failing. Are your belts tightened to spec? Could also be the belt slipping on the pulley.

[Razorback1980]

Water pumps are a shaft driven impeller. The only way they do not pump is if the impeller is not connected or slipping on the shaft which is almost never. The slipping of the belt is a possibility, but I'm hoping your timing belt is not that loose...otherwise you will have bigger problems like bent valves. The higher the rpms the faster the impeller turns which circulates water better of course the law of diminishing returns does apply here. The most common way water pumps cause overheating is the seal starts leaking coolant past it and it runs out the small hole in the bottom of the pump causing your coolant level to go down. When you are feeling circulation in the hose, you are actually checking the thermostat to make sure it is open and allowing coolant to flow through the system. One other thing to always check on the water pump is up and down play on the shaft to make sure the bearing is good. If the shaft moves up and down, the seal will leak and you will lose coolant. Fans are very important, pay very close attention to them. They don't wait until the car overheats to come on, they come on at a certain temperature and since your car cools better at high rpms which translates to your car moving faster, the problem is probably with your fans. Make sure they work the way they are suppose to and make sure they both work. They are critical to the cooling of the 944. Considering that yours is going high on the gauge and then the thermostat opens, that makes me suspect the thermostat is at least partially the problem. They are cheap, replace it. Next make sure both fans work and work properly. Check Clarks-garage to test these. The third thing to check is to make sure your gauge is reading correctly. I use a thermometer on the engine to read the temperature and see if it is relatively close to the same as my gauge.

[Tishabet]

I think Razorback and I read your "RPMs" comment differently. I assumed you mean higher RPMs with the car sitting still and you reving the engine. Did you mean higher speed?

[Razorback1980]

Good Point Grant...either way will decrease temp some. But should be much more with higher rpms and car moving.

[Baza]

Just a thought. But what about the thermo fan switch if it is reading incorrectly and coming on later may cause the problem. If not over heating with high revs water circulating faster coolant not heating the switch, as oppossed to slower coolant staying hotter due to coolant staying in the motor longer. Find someone with a infer-red temp sensor and check the temp of the head when the fans come on mine comes on at 85deg but they range from 75-92 this will tell you if it is the thermo switch or temp sender. at $13 it would be my next step then $20 for temp sender

[twerp129]

Thank You, so much, for all your help, I work 70 hrs a week and have a hard time finding time to test these things but Ill get to it eventually, I have a mechanic friend with a temp gun also.

At first I was overwhelmed american cars are simpler. . . err. . . different, but its not so complicated after all, though I believe I will have to sell it(944) before winter, need a cheaper, Sports Car (Mk2 VW GTI, 1gen. Rx7?) I have to go to college.

Also, I was refering to the higher RPMS driving, and it seemed, highway driving in 4th gear was alright, but when I got to stop and go city it starts to heat up. But thats great, check the cheap stuff first?

[Slam]

Do your coolant hoses pressurize as the car heats up?

[SD_944_2.5]

Im in the same boat. So far I have replaced fan, thermo switch and relay. Still the same thing the temp shoots right past the third hash. I retested the fan, it works, the relay??? I dont know yet, but it seems I spent over $300 on parts I didnt need. So my next question is where is the temp sensor? Maybe thats it. Back to garage.

[SD_944_2.5]

Ok now to make matters worse, how do you jump a thermoswitch that has three prongs? After 14 hours of trying different things I found out that the ac swtich somehow controls the rad fan..ie...rad fan doesnt work until the ac switch is activated and the freaking thing still overheats. ERrrrrrr. No whine from h2o pump, and the fans, thermoswitch and relay have all been replaced, there is pressure in the hoses when car is running. So its sounds like either thermostat or pump????

[Razorback1980]

Check this link, it will explain everything for you.

http://www.clarks-garage.com/

Then go to COOL-01 (Testing cooling fan relay on late cars)

[SD_944_2.5]

Thanks, I felt the lower radiator hose and it was cool, after the temp got over the 3rd hash mark. Well back to the garage and taking everything apart again. This time I removed and flushed the radiator out, and now am in the process of taking out the thermostat. This is the last ditch effort.......

[Razorback1980]

Sounds like you have the right plan. The other thing is to make sure you bled the system very well.