951 Running hot
 

I have had my 86 944 Turbo for about 5 months and have been battling the issue of running hot/occasionally overheating nearly the whole time. It's not consistent in when it shows up. I have bled the cooling system 50x. The pump is new and I replaced the thermostat. The thermo switch was bad so my fans now work but it doesn't keep the car from reaching the 2nd white line. I have the coolant level just above minimum when cold and when it's hot, it will go over the max line, like it's got excessive pressure in it. It consumes a little coolant, but I can't tell if that's from an occasional overflow or somewhere else. Last night I pulled the plugs. The actual tips look about the same across all 4, but the threads of the #4 plug are clean where the other 3 are darker. I did a compression test last night when it was warm (and the throttle wasn't opened up) and this is what I got: #4 was 130 psi, #3 was 145 psi, #2 was 140 psi and #1 was 147 psi. So a different of 17 psi from lowest to highest. With the same test at WOT the readings were 140/150/150/150.

I am thinking I have bad head gasket (Hopefully not a damaged head) do you agree? My last test is to test the coolant for exhaust gases this weekend.

I am located near Waterbury, CT. Does anyone know of a reputable machine shop that can inspect/repair my cylinder head if I have to pull it?

Thanks for the help!

Hey you responed to my similar post. The main difference is my car has never gotten hot per say other than typical stop and go idling when warm out short of second white line and fans kick on bring it back to 1st white line. Let me know if/how you check for exhaust fumes.
also haven't done a comp. test yet. I'm an east coaster too NE Pa.
Ron D.

So I tried to test the coolant for exhaust gas but after running the engine for about 4 minutes with the cap off, the coolant just started overflowing out the expansion tank. I definitely think mine is a head gasket forcing pressure into the coolant passages.....I hate to tear the top of the motor out without being 100% sure but it's looking like that's what I am going to have to do.

This is very common with 944. Almost all 944s that we work on will start to slightly overheat when left at idle for a long enough period with a 1 bar pressure coolant cap. The water pump is not really designed to circulate efficiently enough at 800-900rpm and will get above the 2nd white line if left long enough and even the fans will not bring the temperature down as there is insufficient circulation to push the cooled coolant back into the block effectively. On these cars we see if we bring the idle up with the pedal to say 1100rpm the temperature will then start to come down.

The other issue is that these cars do not have an expansion tank for the coolant to be dispelled into, unlike almost every other car on the planet that has an expansion tank after the radiator cap. What we do is put a small 2-2.5ltr plastic tank in the inner guard with the tube going all the way to the bottom of the tank. this is needed so that when the car does expel some coolant it will be able to capture it and also suck it back in once the car cools down.
Regards
Sean

Thank you Sean. Do you think it's ok that the car started to expel massive amounts of coolant after running for about 5 minutes with the cap off? (So that I could get the coolant test in the opening of the coolant tank. That seemed odd to me.
Thanks,
Kevin

Yes absolutely. the water/ coolant is being boiled up by the engine.
Probably the best way to test if your head gasket is breached would be to put some clear tube on the coolant tank over flow and have it sit up near the windscreen so you can see it. Go for a drive, when you create boost is you see coolant being forced out the clear tubing then you either have a head gasket going or a bad radiator cap

You can also test your coolant for exhaust products which would confirm that you have a leak.

https://www.harborfreight.com/combus...MaAsZQEALw_wcB

I tried testing that, and although I did get some coolant in the test tube (It overflowed rapidly into the expansion tank when I had the tube in it), I did not see the fluid turn yellow or green. I might try it again. In the meantime I have swapped radiators to see if that is the issue but have had a very hard time getting the proper amount of coolant back into the engine/radiator. I ended up removing the neck that has the bleeder screw on it and filling the engine that way. To me, that indicates something still isn't right, but a bad head gasket wouldn't cause that. I am wondering if the impeller on the water pump is spinning free from the pulley? it is a new pump (Not installed by me) and I replaced the thermostat.

are the radiator hoses getting hot to touch? if they are then you have flow

When the engine temp sensor was in between the white lines (Around 85c?) the radiator hoses were 45c (Upper from the water neck) and 30c (Lower, into the water pump). Weird, right? The cylinder head at the location where the temp sensor goes in was 85c. Farther back on the head was 57c...I used an IR gun to read.........

is the radiator original? Could it be the radiator has restricted flow and coolant is not passing through quickly enough to cool.

I suspected the radiator and replaced it with a known working used one. Same issue exists. I've continued to delve into what is going on as it's driving me crazy. I truly believe the coolant is not circulating through the system. I suspect it's pump related even though it is new. Yesterday I noticed the coolant tube that's above the header was 250c with my IR temp gun! And the pump housing was like 55-60c so the thermostat wasn't even close to opening. No doubt coolant is boiling at 250c and causing the pressure I am seeing in the expansion tank. This was after only about 5 minutes of the car running! So the hoses and radiator are like 50c when the temp sensor in the head is like 95-100c and the water pump housing is like 55c....
I also wondered if my exhaust is building up so much heat for some reason that it's overheating things as well...Not sure about that but I am about to tear down and replace the pump as well as all hoses...

I had a similar problem. Pressure bled the system and it was good after that. Was making me crazy too!!

Mike G.

Always a good idea to drill some holes in the thermostat.. highly doubt you need “ real” heat and car to warm up fast because typically these are now fair weather cars… helps purge the system …

Always check Clark's Garage info - and donate! My '86 951 is chipped with a modified turbo, cam, headers, etc. I have blown the head gasket 3 times in 25 years. Invariably the coolant tank starts to overflow, sometimes violently. So about 15 years ago I rented a compression test kit from AutoZone and I bought a Cylinder Leakage Test kit from Harbor Freight. The throttle-open compression test showed only a +-2.5 psi variation around a nominal 137.5psi. However, the Leakage Test instantly found the blown head gasket. My shop air pressure was throttled carefully into the #4 cylinder spark plug hole. As soon as I started to open the valve I heard and saw bubbles in the overflow coolant tank! #1,#2, #3 cylinders were fine. Mike Lindsey earlier told me that #4 is usually the trouble spot in 944s - he was right in my three experiences. Mike likes to use new Porsche OEM head studs but after chatting with several other 944 advisors, I went with the ARP 204-4211 heat stud and nut kit which contain a unique thread lubricant for precision torquing of the nuts. I used 3 stages of tightening 40 lb-ft, 70 and finally 100. ARP has white papers detailing this lube and correct tightening technique. Being OCD I had the local SnapOn tool truck mechanic calibrate my torque wrench at 100 lb-ft. It was off less than 0.7 ft-lb. Back around 2007 I sent my engine to Lindsey for a complete rebuilt including adding stainless O-rings to the head as extra protection against blown head gaskets. Most high-perf motorcycles have O-ringed heads. So now with ARP studs and O-rings my engine might have a little better luck. Next time I might check into High Boost and Tomei embossed steel head gaskets.

After the head gasket repair, I changed all of the coolant hoses and a final coolant pressure test found two pin holes in my radiator. 944 is the gift that keeps on giving. Also check the coolant tank cap, old ones can leak. FCP Euro is a bit $ but they warrant their 944 hoses for life. 944 Online has an upgraded hose w/ heat shield fabric for the turbo coolant line and what they call a Stage 3 Cooling System kit. My twin fans and the temp sensor/senders work correctly so my car's temp gauge is normally at the 1st mark about 1/3 up the scale. When getting hot it heads almost to the 2nd mark but fans bring it down quickly. In June 1986, Porsche published a Tech Bulletin #1 regarding a new main thermostat for all earlier 924's and 944's. This bulletin also has details of an upgraded water pump and a modified water pump belt tensioner and belt routing which involve removing material from the black plastic belt housing at the front of the engine to allow the new belt routing. Check Lindsey too, they have a neat kit that fits a short hose to the original radiator drain plug hole then adds about 12" of hot water hose and terminates to a mini-hot water valve. This on/off valve and hose makes draining the coolant system easy - and no more mess! After using this drain hose, it stays mounted to the radiator and I zip tie the loose end up and out of the way - until next time.