Porsche Enthusiasts Club Forum

Hi all,

I have an '82 944 Lux which has got the following issue:

When stsrted from cold and left on tickover it warms up as expected, stat opens and rad fan comes on and off again.
But, when it is driven from either hot or cold the stat stays shut and temp guage climbs quickly up to 3/4 and the fan doesn't come on because the rad is cold. If I stop and leave it on tickover then the stat opens, rad warms up and the fan comes on.

I have changed the stat (Porsche one) flushed the system, refilled with new coolant and am confident that the system is completely bled.

There is no water in the oil or oil in the coolant, but on a recent cautious journey of about 20 miles it did use some coolant, plus on start up from cold if I gently rev it there is some slight blue smoke (oil)

I suspect a head gasket fault, but would welcome suggestions.

If it was just using coolant, I would get it pressure tested first, but I don't understand the stat thing ???

Thanks in advance

Is that radiator flowing correctly?

Seems to be.

I had a hosepipe and flushed it through in both directions - didn't notice any waterflow problems.

944s can be a pain to bleed. I know it took some time to check mine out despite bleeding it from the top nipple. Pressure bleeding really works here.

Have you attempted to bleed it again?

I've bled it quite a few times now. But there seems to be a variety of methods.

This is how I did it:
Park car with front raised and heater on hot.
Fill system with bleed screwopen until steady stream of coolant comes out of screw.
Tighten bleed screw and start car with expansion cap removed.
Let car warm up on tickover and keep expansion tank topped up to max.
Check stat opens correctly and rad fan comes on correctly.
Let rad fan come on twice and also burp air into expansion tank by squeezing hoses.
Refit exp cap, start car and let rad fan come on twice.
Switch off and open bleed screw until stream of coolant comes out.
Let car cool down overnight.
Start car with exp cap off and run on tickover until fan comes on, burping hoses got a small amount of air into exp tank.
Refit exp cap.
I then took it for a drive and about a mile up the road pulled over and stat had closed.

I also noticed that when the fan cuts in with the exp cap off, the water level in the exp tank drops a fair bit - any ideas.

I have a reasonable mechanical knowledge, but this has got me beat.

Personally I would pressurise the system (you can mock something up with an inner tube and a bike pump) and rebleed.

Other than that I would check your bleed off hoses (they could be full of gunk) and even the expansion tank itself ; they do wierd things when they get old (i.e seal and not seal as they heat up.

The stat does not 'stop working', assuming it actually works(have you tested it off the car?). If it sees coolant at the required temp it opens, irrespective of whether the car is idling or not. So either its not seeing the temp (air in system), or coolant isnt flowing (blockage, water pump fault). However as it overheats on the move rather than at idle confuses the issue. Can you verify the gauge works? Id get the system pressure tested and do a sniff test before proceeding.

Impeller spinning on the shaft?

This might be it. Hadn't given the pump any thought as it was replaced about 5 years ago.

Thanks for all your help.

Will try a pressure bleed first and if that doesn't work get a sniff test (combustion gas leak test) done.
Probably just as well to get compression checked at the same time and blood pressure

Does anyone know where I can get a coolant pressure tester from?
Spent all afternoon looking and can't find one that says it fits a 944.

Jefft a cylinder leakage test will tell if a head gasket etc is at fault first, if ok then remove the thermostat and test, if ok check water flow to confirm pump is ok.

Always run engine with a good thermostat, always run engine with the rad cap in place but topping up to max level from cold, do not remove cap when hot.