Porsche Enthusiasts Club Forum

I'm trying to get an overheating problem sorted on my early (84) 944. It seems worst when driven enthusiastically (typically in second and third gear), when the temp gauge sometimes goes to max. I occasionally rally the car, and she gets very hot doing tests and while queuing for the next one. Not quite so bad when in normal day-to-day traffic when revs are of course much lower. I have flushed the rad, replaced the head temperature sensor and today I bled the cooling system - lots of air bubbles up through the header tank when I squeezed the top hose, not many through the bleed screw - is that normal ?

When the temp gauge gets to the bottom of the solid sector, the fan comes on, it all cools down and the fan goes off again - which all seems fine except that I would expect the fan to come on sooner. I did notice that when the fan comes on it blows hot air forwards through the front panels, and the air is certainly cooler between the fan and the engine. Is that as expected ? I guess the heat has to go somewhere, but how effective would that be when the car is moving ?

The temp gauge behaves as you'd expect, no jumping or sudden changes, just reading very hot. Could that be an effect of a poor earth from the gauge ?

I have been warned that overheating could be a symptom of a head gasket on its way out, but then I would expect the coolant level to drop it that were the case.

I had similar symptoms and spent forever trying to sort it, and plenty money. Turned out that the timing belt, which drives the water pump, need tensioning again. Early model cars don't have any kind of spring tensioner so need to be checked regularly (every few thousand miles). It is possible to do as a DIY job.

The fan sucks air through the rad, it does not blow forward

Something is not quite right there

Indeed, it's akin to pissing against the wind. Try a pressure test on your sytem also. Thermostat and water pump may be at fault. I use Staycool from Frost, a corrosion inhibiter which also claims to run the sytem cooler with premixed antifreeze (the blue one) from Halfords seems to work even on track days. It's very dangerous to run hot, my previous engine had blown the head gasket at some time and suffered bore scoring. But you need to check that fan first, sounds like reversed polarity, very odd how that could happen.

bet someone has fitted the wrong fan when they had one fail sometime in the past

Thanks all - I shall certainly check the timing belt. Thermostat is new (and yes, it is the correct one, not a mini one which I have heard looks the same but has a smaller bore). The fan has certainly got me puzzled - but even if it is somehow reversed, it still doesn't come on until the needle reaches the bottom of the top (solid) segment of the gauge - IYSWIM. It would be great if anyone else with an early car would run their engine until the fan comes on and see where the needle is on the gauge and where the wind blows.

So timing belt tension next, then pressure test the head. Replacing the head gasket is beyond my skill set, so I will have to find a trustworthy and 944-knowledgeable garage to take on that task.

Don’t be ruled by the gauge, it might be miles wrong, also have you changed the rad switch which switches on the fan, it’s tucked up under the top hose on later cars, I am definitely not an experienced person on the early cars

I would go buy one of those infrared gun temp sensors, they are about £15 on eBay well worth the money

Yes, I do worry that maybe it's only the gauge that's the problem. Next time (!) I take the dash apart I'll check the earths very thoroughly. As I understand it, the block temperature sensor on the early cars drives both the gauge and the fan (the sensor actually only measures the temperature of the block, it's not immersed in the coolant). One point which might be of interest for anyone else who stumbles on this thread is that the old sensor was only half screwed into the block, so I guess the engine would have had to run hotter in order to get the sensor to react.

I do have one of those gun thermometers, but I don't know what it should read for any particular part of the engine ! The top hose got to about 80 degrees.

The rad fan switch in the later cars with twin fans, switches on lower at 94 and high at 102 degrees

That might give you an idea of how warm it should be, anything over 100 is boiling water

Clark's Garage has details on gauge troubleshooting (Garage Shop Manual > Electrical > Gauges > Gauge Troubleshooting), including a procedure for testing the temperature gauge with a potentiometer and a diagram showing the temperatures indicated by the marks on the gauge.

Michael