Matt O.

968 runs hot, fan stays in the highest mode it goes (once it gets there, which doesn't take long). Temp bar is parallel to the horizon, but stable (doesn't drop a bit when the fan kicks in). It's like the fan is barely cutting it. I've had several 944s including the "S3" and the fans never worked this hard, only to keep it mid range. It's only 84 degrees outside.

I have a little residue around the lower radiator hose, where the smaller one (above and right of the lower) exits the water pump/thermostat housing. I recently purchased a replacement plastic seal for that piece.

But I don't think that's my main issue. Just drove it again tonight, and there was no leakage out of that seal. But the 968 still ran very very hot.

Upper hoses are hot, lower is hot, and the one going into the cylinder head is VERY hot. Coolant reservoir is hot as well. After roughly 15 mins of driving.

Can't quite pinpoint this. If it were a water pump, the lower would be cool and the upper would be hot, or vice versa, correct?

Same for a thermostat failing to open?

Thanks in advance.

JDS968

I'm confused, why do you think it's running particularly hot? When you say parallel to the horizon, you mean the needle is horizontal? That should be roughly half way between the "normal" range lines. Mine usually runs closer to the lower "normal" range line in highway driving, but can sit around the middle of the range or higher if in slow traffic on a hot day. What driving conditions is this occurring in, and is there any difference between driving in slow (or stop and go) traffic vs highway?

Both a stuck thermostat and a failed water pump would result in at least one of the radiator hoses being much cooler than the other.

The cylinder head under perfectly normal operation should feel VERY hot to human skin. You might want to get a hand held IR thermometer, they've very cheap and can be quite useful for diagnosing all sorts of things in the engine bay.

How did the problem develop? Running cooler and less fan operation last week, suddenly running hotter and running the fans more this week? Slow development over a period of months? Parked it for a season and then started it up this weekend, noticed the problem?

Matt O.

Last I drove the 968 was about a year ago. It did this then. I stored it for a year, and changed oil, new battery, and took it back out. It seemed odd a year ago and it's certainly odd now. I'll check out the IR thermometer.

I believe it's running hot simply based upon my experience with these engines. Something just does not seem right about it. Fan blasts full speed at all times, even on the highway (it is audible at full speed).

I understand the cylinder head should feel hot. But I'm trying to figure out what would cause the water to get even hotter. I have not ruled out water pump or thermostat. I'll see if I can track down the thermometer.

Yes, parallel to horizon, meaning horizontal. Past experience tells me a healthy cooling system in a 944/968 is normal operating is just over first bar, and if it creeps up (stopped at a light on a hot day) to the mid-range to the second bar, the high-speed fan will bring it back down. The high-speed setting on the fan kicks in at the appropriate point, yet stays on, needles doesn't budge, and that's that.

I don't recall, what temps should I see normally at full operating temp?

RL911

Mine sits just above first bar, maybe half a cm. maybe your temp switch is failing. You can install a low temp switch, which should help. Easy install, but you will need to drain it. Located on drivers side near top of radiator.

The other thing it could be is air in the system, have you tried to bleed the air out from the bleeder screw?

When was the last time you changed your fluid and what did you put in?

Matt O.

Yeah I bled the system well when I did the flush. I'll re-bleed just in case that's part of it. Porsche pink coolant went back in after a thorough flush (about 15 bottles of distilled water). I didn't think of the temp switch going bad. The lower temp switch will simply kick the fans on earlier, correct?

I need to determine with the thermometer if I'm smoking crack or if she's really running hot... Thanks.

JDS968

I don't see how a temperature switch failure could lead to the fans failing to lower the coolant temperature effectively even running at maximum speed.

I'm smelling that the coolant temperature gauge is reading inaccurately and the car is actually running at normal temperature, but you have nothing to check the gauge against without a thermometer.

Alternately, maybe you have a restriction in the radiator, leaving you with enough coolant flow to keep the engine from overheating completely but not enough to cool it as well as normal?

Thom

If they are equally hot, then coolant flow may not be high enough, suggesting blockage in the coolant circuit, most often caused by a thermostat stuck closed or at least not opening wide enough.

If the water pump was not flowing enough I'm pretty sure the coolant gauge would go through the roof and light up the warning bulb.

Can you find a long steep road and drive downhill with no engine load, just engine braking, say starting from 4500 rpm in 4th? Coolant temp should decrease noticeably quickly to below the second white mark on the temp gauge (which represents 80°C). If not then it would confirm a blockage in the circuit.



The fans running at high speed should always be able to drop the temp down (very) near to the 80°C mark when the engine is left idling.

Btw coolant enters the rad through the upper hose coming from the head and leaves it from the lower hose. Just thought I'd mention it since your post suggests you are unsure which direction the coolant flows into the circuit.

Matt O.

Thom, thanks. Yeah I couldn't remember. Last time I worked on the coolant system in a 944/968 was 2002 when I replaced every component of the cooling system in my 89 944. Never got above the 80 deg mark, even on hot days. Worked awesome after that. So it's been a while.

Going to the store now to get a thermometer...

Thanks.

Matt O.

Ok, got some temps.

These temps are at full operating temperature, after highway driving for 10 minutes and city driving for 5. They were taken after 5 minutes of 25mph driving to get back to the house. Taken with the front end in the garage, out of the sun, car still running/idling. The temperature outside is 100F, however this issue I'm having at all times, in addition to last night when the ambient temp was 84F.

All temps below in C.

Full operating temperature lower radiator hose 62.40
Full operating temperature smaller lower hose to water pump 64.6
Full operating temperature upper radiator hose to cylinder 85.2
Full operating temperature expansion tank 77.2

TIA.

JDS968

I would suggest taking a slightly longer drive to make sure that the temperature of the outer surface of the hose is as close to the temperature of the coolant inside as possible...but I'm going to take a guess here and say the temperature differential should be within 5 degrees C...which would equate to around 90 degrees, about what your gauge is showing.

The difference of more than 20 degrees C indicates that your radiator and fan are in fact bleeding heat out of the coolant effectively.

I'm curious, now, whether your engine is somehow generating excess heat, maybe due to lean combustion? Have you checked your plugs?

Matt O.

Just did another drive. Lower hose was 60+/- 2, upper hose got up to 92 and was 90 on most shoots.

docmirror

Based on your thermometer results, the cooling system is working right. The thermostat will open fully at 83C. Water leaving the head, and entering the upper hose should be around 90, and leaving the lower hose should be around 70-83. I don't know why your fans are running on high all the time, but the temp sensor in the upper rad is my first guess. The gauge needles in these cars are notoriously inacurate, and now after 20 years, they haven't gotten any better.

The important thing is that your engine is not getting overheated based on the temps you provided. I am thinking that your fans are running overtime, providing excess cooling of the water when not needed.

The setpoint for the low speed fan actuation is 92C, and the high setpoint is 102C. You can test it in a pan of water, with the thermometer. Use the ohmmeter between pins 1 and 2, and heat the water to ~92, the meter should change from open circuit to shorted. Then connect from pin 1 to 3, and heat the water to boiling. At 100C, the upper setpoint should NOT be reached, and the signal should remain open circuit. The only way to test the closed position on the high setting would be to raise the sensor temp to 102, and would require a pressure vessel. You could maybe do it with a lighter just to see if it switched, but the test would not be calibrated.

The fault could also lie in the relay, G10, which is a quad service(two fans, two speeds) relay. The only simple test for the relay, is to start the engine and let it warm. Observe both fans. Both fans should come on low speed first, at the same time. Then, continue to observe the fans, they should switch from low speed to high speed together as the temp rises. Do not use the AC button during the test. If the fans both cycle through off, then low, then high, the relay is working as it should. As the fans cool the water in the system below 92, the fans will then shut off. On model year 92, the fans may also operate after the ignition is shut off to prevent boil off from heat soak. I'm not sure if the later years operate the same.

JDS968

Need to check another car to confirm that the lower hose is as cool as it should be (I wasn't planning on driving my car anywhere until Saturday, so does anybody else with an IR thermometer want to help?) Assuming the lower hose temperature is correct, I'd be a bit worried that you're generating too much heat in the cylinder head due to lean combustion. Would be better if our cars had a thermocouple wired to an actual cylinder head temp gauge (or even better, a set of four exhaust temp gauges, to allow diagnosis of individual cylinders while driving).

JDS968

Problem you have to remember is that he's measuring the outer surface of the coolant hoses, which are made with thick, thermally insulating walls. If the coolant in the lower hose is assumed to be 70-83 C, and is reading around 60-62 C, then we might guess that the upper hose, reading at 90+ C, is carrying coolant at 100+ C. That is getting a bit warm for gentle driving.

docmirror

Which is why I provided a test for the temp sensor. Do you have a test for lean combustion? I do.