kassim

My 928 has been overheating lately but to extreme levels. The other day the temp. reached the upper limit and I stop the car and obviously water was pouring out of the coolant expansion tank. I waited for the car to cool down a bit. Started it and then added water. I checked my fan and the clutch was no good. I changed my fan the same day and still had the same problem. I removed the thermostat yesterday and let the car idle and again the temp. kept rising. This morning I removed the upper hose from the radiator to let the air out of the system and see if that helps. Still cant seem to get the temp. down. Anyone out there know what the problem may be. HELP ! I even openned the coolant reservoir cover and stuck a garden hose in there (while the engine is running of course) and let cold water run in while the radiator upper hose (small hose) was disconnected and let the water run for 10 minutes...the water that was flowing out of the top of the radiator was still hot ! Am I missing something....

StratfordShark

I thought that if you remove the thermostat then you can't seal the bypass port at higher temp, so no coolant is routed to radiator and temp will rise as you experienced.

If that's case then you haven't eliminated a faulty thermostat. Check operating temperature (75 or 83 C) and test it in a pan of water as you heat it up.

Landseer

Could be a number of things.

There's also a very important metal-lined rubber ring that fits a round block port about an inch behind the thermostat. If its decayed, similar to having no thermostat installed on a 928, water will circulate between block and water pump, much of it bypassing the radiator. Dwayne posted a thread, in which Bill Balll made a post, that shows this situation. Could be your problem.

You can't run a 928 without a thermostat. Lots of past posts to search and read.

Here is his epic thread on solving an 84 cooling problem https://rennlist.com/forums/928-foru...-trip-out.html

Mrmerlin

how long does the engine take to get hot, if less than 5 minutes idling then your waterpump impeller may have fallen off.
There might be a seal behind the thermostat not sure but if you do have one then it should also be replaced, be careful about putting the cold water hose to the engine you can crack a head this way.
You should also pull the spark plugs take a picture and post it.
Looking for any of the tips that look very clean and possibly rusted indicate a headgasket leak.
Also you can start the engine with cap off fill the bottle to the top, and see if bubbles come out of the bottle. this indicates a cracked head/block of failed headgasket

Imo000

If you still have the old thermostat, put it in a large bowl of boiling water and see if it opens. It will take a min. or two for this to happend and the water must be boiling. Do this several times with a cool down period (remove the t-stat and run it under cold tap water) between it. I'm working on an S4 that, out of all things, turned out to have a failed thermostat. When I first tested it, out of the car, it openned normaly, then for the second time only went half way and after that, never openned again. Even when I had the old and the new t-stats in the same bowl, side by side, the new one openned all the way and the old one didn't move at all.

When it sarted to owerheat, was the lower rad hose, at the thermostat housing, cold? How about the radiator, was the driver side cold (showing no circulation)?

Does it overheat even if you are moving (over 25mph)?

Lizard928

if you remove the thermostat then the car will overheat.

Lopez

+1 - this happens sometimes. Does coolant flow back out of the radiator on its own after the engine is warmed up (with a working thermostat)?

jheis

This happened to me recently. Car would go from stone cold to overheating within 5 miles of freeway driving. Turns out that the Laso water pump had seized solid after only 36,000 miles. Fortunately it didn't machine the block ....

James

Mongo

+2 or 3 on the waterpump impeller. It's probably spinning on the shaft rather than turning with it. Had that problem before on a 944.

kassim

Thanks for the great responses guys...I even tried installing a high performance electric fan but that did not help either. I guess I'll put in a new thermostat and see if that solves the problem. I know on my other cars when you remove the thermostat the cars never get hot so I was surprised when I saw the responses...lets hope thats the problem. I'm keeping my fingers crossed !

ImoOOO: I felt both sides of the radiator and the passenger side seems to be much hotter than the driver's side. Also the top of the radiator was hotter than the bottom. I didnt check the radaitor hose at the thermostat housing. Which one should I check ?

I also removed the small hose just below the air filter that goes to the heater unit (I think) to check if water comes out...it did but just barely. And when I reved it up the amount of water increased but not like openning a faucet or a hose. How strong should the water be coming out of there. Or is it because I dont have a thermostat in there ? I also noticed that there was an inlet also below the air filter more towards the passenger side that had nothing attached to it...dont know what that is either.

Mrmerlin: It probably takes 10-15 mins before it gets up to half way/three quarters on the gauge. I'll remove the plugs and try and post some pics.

Mrmerlin

make sure to order a rear thermostat seal unless you know you dont have one in the water bridge.
If this part isnt good then it could cause some of the problems your having

Imo000

Since you have the thermostat already out, Put it in a cup of boiling water and see if it opens.

Bill Ball

+928 if that wasn't made clear.

Bill Ball

If it really overheats from cold in 5 minutes, then I doubt the t-stat is the issue. This points more toward NO COOLANT FLOW - i.e., bad water pump. Initially the pump pushes coolant though the block and distributes heat providing some cooling. THEN as the water warms up, the T-stat CLOSES off a bypass pathway that recirculates the block coolant and redirects it to the radiator. Notice how this is different from American cars and shows why the T-stat is needed to bring the radiator into the flow loop. Water should then flow briskly to through the upper radiator hose to the radiator and out the bottom hose back up to the cooling bridge fitting with is right over the T-stat. The radiator should be about 30 degrees cooler in the bottom left hand corner than the top right hand. Figure 195F entry, 165F exit.

If you reinstall the t-stat, make sure the sealing (flat disk) side is facing rear and the large o-ring is in FRONT of the outer lip of the T-stat. Removing the T-stat made things worse, but I believe, as others have said your problem is elsewhere. DO NOT LET THE WATER TEMP EVER GET INTO THE RED ZONE ON THE GAGE or you will end up with bigger problems.

If you car is 87-89, check that the airflow control flaps in the front bumper nose are not stuck closed. This will not cause extremely quick overheating but it can be a problem.

hacker-pschorr

We need a visual on the rear T-Stat seal:

REPLACE THIS SEAL!!



From this post:

https://rennlist.com/forums/4942201-post15.html