catflab

Hail my fellow Rennlisters,

[background info] So the sharks come a long way. When I got it, it hadn't been driven for 3 years and basically nothing worked. A thousand dollars down the line, it was running and the sound of the motor was sweet music to my ears. I had hope.

At one point (much too shortly after) it stalled and 2 cylinders failed on me ... the mechanic gave up on the car after this. I refused to believe it was the headgasket or heads ... partly because I couldnt afford it, but again, I had hope!

So, I switched mechanics and another 600$ down the line, he fixed the intake manifold, a vacuum leak, cleaned our gas tank out (he said it was a abysmal) and replaced an injector. I also installed a new air filter, heater valve, and Temp 2 sensor.

The car ran awesome after this!! I was easily getting it up to 120 on the highway. Still have some minor shaking when idle but nothing too crazy.

[actual problem]

Much to my dismay, after my first day of joyriding the new and MUCH improved shark it overheated. I had noticed it was running hot (the temp gauge was always almost at the 2nd line) It overheated NOT during hard riding but just cruising down a busy street. I pulled over immediately and let it cool off .. thereafter, it would always overheat after 5-10 minutes of driving. I could hear the coolant boiling inside .. not good!

My friend opened the coolant tank cap a fool and it sprayed everywhere. I added more coolant .. that still didnt help.

These are the clues I have noted:

* the car used to blow ONLY hot air, now, it will only blow cool air (it is almost winter here in NY, so it's pretty cold outside)

* Even with the FAN control and AC OFF, the car does blow hot air through the windshield defroster exhaust vent. I cant stop it, before it didnt use to do this.

* The electric fan by the radiator does not turn on anymore.

* The radiator is barely warm to the touch on the left side, getting a little hot only when the temp gauge is almost to red.

* the right side of the radiator is much cooler.

* the left hose which i assume holds the coolant is very warm, and there is pressure inside but it is not hard to squeeze.

* the right hose coming out of the radiator is very cool to the touch.

I'm hoping it's the thermostat, or maybe a clog in the radiator. I really do not know enough mechanically to diagnose the problem further - but I also realize that it might be the water pump (gulp!)

I would really appreciate any advice on this matter ... I mean, my heart soared during those few hours I got to drive the car. It was an improvement by leaps and bounds from before. Now, my heart has sunk to my stomach with this overheating problem, and I'd love to get her back on the road ASAP!! Any ideas?

Jim_H

What year is it?
5 Speed?

If its an 87 or newer do the fans come on when you run the AC?

Imo000

Sounds like a stuck thermostat. It's stuck in the closed position. If you can, remove it and put it in a cup of boiling water. You should see it open. If it doesn't the thermostst failed and collant can't circulate.

Jim_H

Why isn't his fan coming on. I am guessing because the water isn't hot enough to trigger the sensor and this is a pre 87?

UKKid35

I'm sure you know this already, but the all aluminum 928 engine really doesn't like to be overheated, you will warp and crack things.

Lots of useful info on Pirtle (as usual) http://www.nichols.nu/cat22.htm

FlyingDog

If it's a 16V the electric fan is only for A/C I think. It may work alos at a very high temp theshold, but I'm not sure.


Thermostat would be my guess for the overheating although it could be a clogged radiator.

Did the A/C and heat problems start after a trip to the mechanic? It sounds like a vacuum problem.

IcemanG17

Model year would help, but it does sound like a bad thermo, which makes sense with its lack of use for a while. But it didn't overheat before it was fixed? Thats odd?

If its an 87-90 it could be a air flap problem, but it doesn't sound like it...more like a thermo or maybe a cooling fan failure?

Your other problem of only blowing cold air could also be the thermo or it could be a vacuum problem like what I had...read this thread:
https://rennlist.com/forums/showthre...ght=heat+fixed

Spikeysash

I am the second owner of this 928, the fool that opened the coolant tank and let antifreeze spew out. The car is a 1985 euro. Thanks for all the help guys.

Btw: I don’t know if this helps or not but the coolant light was always on before the car was taken out of the shop and filled with coolant.

pvoth

after checking the themostat try checking the ignition timing too this can cause over heating
heat is a killer more so with alumimium..be careful

p

SharkSkin

Note that on the 928, the thermostat being stuck in the OPEN position will cause the symptoms described. The thermostat CLOSES to force flow through the radiator. Some folks get confused because the thermostat actually balances flow between two passages; when cold, the radiator return closes. When hot, the bypass passage to the pump closes. What you are looking for is for the t-stat to close and eventually seal the rear passage when hot. There should be a rubber seal in the smaller hole in the water bridge that the t-stat seals against as well; if it's munged or absent you won't get full flow through the radiator.

WallyP

Three main possibilities. Starting at the easy end:
- Air lock in the cooling system. The 928 system needs careful filling and bleeding. Have the nose high if possible. Remove the small vent line fron the radiator. Slowly fill the coolant tank until coolant flows from the vent. Replace the vent and continue filling. When the coolant tank fills, burp the system by squeezing the radiator hoses. Crank the engine and get it warm (leave the cap off). Being careful to stay away from moving parts, squeeze the hoses some more. Keep the tank full. Drive the car, checking the coolant level before each trip.
- Stuck thermostat. Replace the thermostat with a standard temp 928 thermostat from a 928 vendor (so you get the correct O-ring). Naturally, we are the best 928 vendor... Check the seat in the housing, be sure to get the seal on the correct side, and fill as above. WARNING: you can NOT run a 928 without a thermostat!
- Failed water pump. Replace the water pump, timing belt, rebuild the tensioner, check all the rollers, replace the tensioner arm bushings, etc., etc.

If there is no coolant flow, the fan sensor never gets hot enough to turn the fan on.

The interior air flow problems are almost certainly vacuum leaks in the HVAC system. A search will give the test and repair methods.

tv

Hey Guys,

Congrats on the perserverance!I also own an 85 euro. They tend to run a little warm because they tend to run lean and the mechanical fan is no good and airflow is a challenge.

Heres what I did.
Add 2 RRFRPR's from wallys store and get the A/F right.

Replace mechanical fan with electric.

Remove all the crap in front of the radiator(i don't use AC)

Take radiator out and air pressure hose all the pebbles and grime in between the fins

Flush your cooling system (easy job)

Clean the parts of the engine you can get at (clean engine cools better)

That should do it. I can now let my engine idle until the cows come home without any climbing of the temp neddle. The electric fan in front of the 2 rads is triggered by the head sensor on the 2nd spider arm on the passenger side. Not a problem on mine as the fan was one of the things i removed. All it does is block airflow. Do these things and you should be fine. I really think leaness is a major culprit.

catflab

Hey everyone,

Thanks for the all input. I definitely see the problem in a better light now.

UKKid : I'm only driving the car if necessary for short distances now. No warping my engine!!

Iceman: I'm hoping its the thermostat and its a one-shot-fix but I'm going to read up on the thread you linked too, thanks!

Sharkskin : Right, this had me confused to earlier. The T-stat will def. be priority to check .. thanks for the diagram btw, clears things up

Wally : Yes, this is exactly what I needed! I am anxious to try something myself before giving the car over to the mechanic again.

We'll try burping the system today .. I think we can manage to do it, but as I said we are pretty mechanically limited in knowledge.

Either way, I'm going to print this page out and give it to my mech. I'm sure it will be worth its weight in gold!

P.S. TV: whoa, I have no idea what RRFRPRs are - and why is the mechanical fan no good? Maybe we can discuss this further if you have time ..

jetrainor

Just my 2c worth. After doing TB WP and new thermostat my car ran at the upper range of the temp guage. It had never done this before. Put another thermostat in, burped the coolant system and still ran hot. Shortly after, a rod bearing went. Are these events connected?....not sure but i suspect so.

87 euro auto

FlyingDog

RRFPR is a rising rate fuel pressure regulator. Unless your car is modded, you don't need one. The mechanical fan works fine as long as the clutch and bearing are working. My 84 Euro will idle all day just above the first line. It pumps a ton of heat out the exhaust, but the engine stays quite cool with the mechanical fan. Eventually I plan to install an electric fan, but more for space and HP reasons than cooling efficiency.