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Location: Warner Robins, GA
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Overheating problems!

I have to keep this short because I'm going in to work now, but I can check during my break.

The past week, my car overheated for the first time. I though it may have just been because there was air in the system and it was low on fluid, so I cracked open the blessed and followed the steps provided by Clarks garage to get the air out, and my tank was filled up. About 4 days later (today) my temperature was all fine, until I was a block from work and I noticed the temperature had sky rocketed. Not to the point of warning lights coming on, but just close enough to scare me.

I have a feeling I might have to bleed the system again. Any suggestions on what it might be? WP and TB job about 3 months ago. Do I have a leak somewhere that is allowing air? Thanks

86 944 N/A
Old 07-19-2010, 01:02 PM
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for a basic test: let car idle and see if both fans turn on when it gets hot, you can race the motor a little to speed things along, watch the res to see if bubbles are coming in a sign of headgasket failure
also make sure when they turn they are pulling air in thru the radiator
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Old 07-19-2010, 02:07 PM
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Did you re-tension the TB at the 1600K interval? If it's slipping on the WP that would explain things.
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Old 07-19-2010, 03:08 PM
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I'll give both a try. Funny that you should mention the TB, because the past month, a local mechanic and I we're trying to set up a date that we could get this job done (because I didn't trust myself to re-tension it. I didn't really know how to use the kricket! haha) so after a couple weeks of everything else getting in the way, such as having to replace power steering rack, going to orlando, and him having to go to court for something, I finally decided today that I was going to do it tomorrow.

I hope one of those fixes it. I'll let you guys know when I test it tomorrow. Till then, thanks! And I hope its not a bad WP
Old 07-19-2010, 07:27 PM
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I beleive the water pump should be replaced every "other" timing belt change so you may consider this when doing your belts.

I would recommend re-bleeding the system and be sure the heater is turned on so that water flows completely thru the system.

Also, be sure your are using the correct mixture of coolant to water (check the coolant product for correct mix but usually 50/50). All coolant can cause the car to overheat.
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Old 07-19-2010, 07:33 PM
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So, after doing some testing yesterday, I found that my fans come on when I turn on the ignition, and when I completely shut it off they shot off with the car. I did some searching, and I think its either the thermo-fan switch and/or the relay...you know, the one that costs ~$200 new. I'm almost certain that those are what are causing my overheating problems, and I'll probably knock out both at the same time. I read about the clarks-garage tests I could do to test them (I believe), but I haven't found them. Any suggestions?

Thanks again guys!

Edit: Apparently there are 3 different relays for the 944...944.615.104.01, 944.615.104.02, and 944.615.104.03. I read that the .01 is for 86 and earlier 944s, and the .02 and .03 are for 87 and later 944's. Is that true? Would I not be able to use a .02 or .03 relay in my car which uses a .01? 86 944 N/A

Last edited by hopps; 07-21-2010 at 07:54 AM..
Old 07-21-2010, 07:25 AM
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Things I have learned the hard way over the last month...

You can test the relay by the instructions on Clarks Garage. You essentially manually become the switch by jumping the line to the switch.

http://www.clarks-garage.com/pdf-manual/cool-01.pdf

If the fans turn on as they should then your problem is either the switch or the water in your radiator not coming up to temperature. If the upper and lower hoses get hot then your radiator is probably coming up to temperature.

If the fans don't turn on as appropriate when you become the switch then your relay is probably bad. I would not spend the money on a relay until I had done these tests.

Good luck.
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Old 07-21-2010, 07:54 AM
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Another thing, if your car has air conditioning, if the A/C switch is in the on position, the radiator fan on the passenger side will be on FULL with the key in the on position, late models might have both fans on full, not sure.. If the cooling fans come on when the car gets up to temp, the thermoswitch and cooling fan relay are working.. If you turn off the car and take the key out while the cooling fans were running, and a cooling fan stays running, the thermoswitch and the cooling fan relay, and the slow speed resistor are working..

It sounds like you are loosing coolant. Check all your hose clamps, check for water stains around the radiator cooling fan thermo-switch, it's below the top radiator hose on early 944's, not sure where it is on a late model.

The thermofanswitch may not leak untill there's pressure in the cooling system at temperature, may dry right up after shutting down the car due to the heat in the radiator.

My early 944 had a small weap from the thermo switch gasket, just took some re-tightening to seal it back up.. I probly didn't tighten it enough when I put in the new switch, trying to be carefull not to crack the radiator end tank.

When the car is "cold" remove the coolant res/expansion tank cap, then start the car and let it warm up while watching for bubbles and puff's of smoke in the tank.. Don't run it long, if you aren't hearing bubbles or seeing smoke puffs in the expansion tank after the cylinder head is hot to the touch turn off the ignition, then put the expansion tank cap back on.

If it begins to overflow before you get a chance to feel the temperature of the cylinder head,, shut off the engine. Might want to have a drip pan under the tank/fender area to catch any coolant that might come out.. It's pretty nasty stuff, probly toxic n you don't want it leaking out.. Coolant shouldn't come out but if it's a bad head gasket leak, the combustion pressure might push the coolant out of the open expansion tank, before the coolant is even warm to the touch.. If it gets up to temp, you might get boiling of the coolant, due to no pressure in the cooling system.. The pressure cap is designed to hold a certain amount of pressure to prevent the coolant from boiling in the head.

If you have bubbles in the tank, it's a sign of a bad head gasket..

Another sign is excessive steam from the exhuast but with the amount of water and alcohol they put in the fuel these days, it's hard to tell if the steam is just the warm air/water vapor condensing/fogging. Most cars have steam at warmup, but a bad headgasket usually blows steam all the time, worse as cooling system pressure increases, the added pressure in the cooling system will push more coolant past the gasket, into the combustion chamber.


Alternatively, and less dangerous, perform a leak down test on each cylinder at top dead center/compression stroke, with the expansion tank cap off. If you get sounds of bubling at the expansion tank while doing the leakdown test, you probly have a bad head gasket..

The leaks are usually between the water passage and just one or two cylinders, so you will have to do a leakdown on each cylinder to determine if/where the headgasket is leaking..
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Old 07-23-2010, 10:26 PM
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oh yeah, and the hot hose mentioned above means that the thermostat is working, as well as the water pump.
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Old 07-23-2010, 10:31 PM
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"So, after doing some testing yesterday, I found that my fans come on when I turn on the ignition, and when I completely shut it off they shot off with the car. "
This is prob due to a PO wiring the car to work this way, check for bootleg wiring before ordering a relay.
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Old 07-23-2010, 11:31 PM
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Does your car have AC? is the AC switch off and the fans still coming on with the ignition?

is it just one fan or both?

Additional information.. If the AC is OFF, Do the fans/fan shut off when you turn on the radio?

All these relays are interconnected with multiple possible paths to ground that would allow the condition that you discribe..

I experienced the same conditions, no overheating because I kept an eye on my temp guage, before I could figure out what was going on, I had serious wiring troubles that required hours of work to repair..


Check that the fans spin freely with the key out, maybe even with the battery disconnected.

Ensure that both fans spin without much resistance.. A frozen cooling fan bearing can lead to the problems that I am currently dealing with on my car..

The symptoms that I experienced before I started taking stuff apart were...

The car started to get hot.. The temp guage got to the mark where the fans normally come on, but they didn't.. I pulled over and jumpered the thermoswitch and one fan came on..

The other one was not working at all.. What I didn't realize was that because the fan wasn't turning, didn't mean that there wasn't full battery power going in and out of the fan motor, and, untill the fuse blew.. I still didn't know that the fan bearing was locked, I replaced the fuse... It was working fine because the thermofanswitch wasn't active.. untill a few miles later.. then the fuse blew again and I noticed the temp was at the fan on mark again, with no fans on.. The two times that the fan had power, and all the while while it was turning slower and slower as the bearing failed, before the fuse finally blew, was causing ALL of the wiring leading up to that one fan to overheat. Screwed up some of my expensive relays and a bunch of the wiring..

If your fuse is blown, and the fan is locked up or very difficult to turn, there still may be a short in the cooling system/wiring or a relay is stuck in high current mode due to an overheated cooling fan circuit, allowing the other relays to stay energized.

When you turn on the radio, it causes a break in the current path to ground for one of the other relay's magnetic side, which in turn causes the cooling fan relay to de-energize, untill the thermoswitch is activated by coolant temperature..
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Last edited by cauzomb; 07-24-2010 at 12:46 AM..
Old 07-24-2010, 12:43 AM
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