Beige944

My 1984 944 has been overheating lately, because the radiator fans don't turn on until the temp gauge is in the red zone. I tried replacing the thermostat and temp sensor (the one located on the radiator), but my car still has this issue. Now I'm not sure if there is some other issue, or if the gauge just reads high. Any suggestions?

Emefef

Have you done any other work on the cooling system? Bled the air out?

Beige944

I changed the water pump at the same time as the thermostat, and then bled the system thoroughly. That's the only work I've ever done to it, and it's been doing this for months

Spring44

Did you install a 180 degree or 190 degree thermostat? If you have a 190, then you may not be as far off track as you think. Mine has a 180 and it frequently cycled up into the lower red zone on a hot day and this got me to wondering what exactly that upper temp zone on the gauge represented.

Using an infa-red thermometer, I measured the temperature of the water exiting the engine through the top hose to see what was going on. Turns out the measured outlet water temperature, right before the fan came on, was only 185 degrees, even with the gauge needle reading slightly up in the upper red zone where you might think that it is approaching boiling. My car has always cycled between the mid point and the upper range on the gauge in hot weather, with fans coming on at the high end and cooling back down to the mid point.

The point is that the upper bar on the temp gauge may not be as hot as you assume that it is. It may only be more or less the rated thermostat temperature at the lower reaches of that highest scale and you may not be approaching the boiling point until the far right end of that scale.

I also measured the temp of the water exiting the lower radiator hose and found that there was about 25 degrees of cooling provided by the radiator.
FWIW

Humboldtgrin

Get yourself a coolant pressure tester and pump the coolant system up to 15 psi and see if it holds. If it bleeds down check your hoses and pull your spark plugs to see if coolant is entering your combustion chamber. You may have a bad water pump or worse a blown head gasket. If the coolant system holds pressure then you may want to remove your radiator and clean out the road grim on the condenser and radiator.

thomasmryan

check the low fan speed pucks/resistors and/or wires. your description sounds like the low speed on the fans isn't working

it is best to test a thermostat on the stove prior to installation. (too much work involved if you get a dud)

Beige944

You're right, my low speed fans aren't working properly. Where is the resistor located? I checked behind the glove box but couldn't find it.

thomasmryan

http://forums.pelicanparts.com/porsc...-location.html

I believe it is for the drivers side fan only but check that to be sure on your model

jderimig

{deleted}

Beige944

I went ahead and changed the resistor earlier this week, the car runs perfectly now! Temp gauge stays right in the middle, and I can hear the low speed fans kick on. Thank you all so much, I've been trying to fix this issue for months!

thomasmryan

you might still pressure test the system with the wide heat cycles.

when the aluminum bits get warm, they expand more than the stainless hose clamps. this can squish the hose ends somewhat. (spring style clamps have an advantage as the can expand and contract to keep constant tension). over torqueing hose clamps is pretty common...it makes things worse.

a good clamp will have a rolled edge to keep it from cutting into the rubber. I like a swirl of hylomar on cast fittings for an air tight seal without going conan on the worm clamp. most are 13-15ft-#s

also, look at the glue seam on the heater valve. if its starting to let go, you will see a little air gap through the plastic.