Testing Thermofan Switch

[Mask of Destiny]

Finally got my 944 back from the shop Friday for a waterpump replacement and soon had problems with the engine getting too hot. The fan will turn if I jumper the thermofan switch wires, but I haven't gotten it to turn otherwise (well I think so, it was a bit dark and the engine may have cooled a bit by the time I found my flashlight). I want to do one more test after I rebleed the coolant system before I go to the trouble of taking it out of the radiator for a proper test.

My question is, how far up on the temperature guage does it need to get before the fan usually turns on?

[Techno Duck]

With the early temp gauge on my 924S, i would see the needle go slightly past the 3rd line before the fans kicked on.

[Mask of Destiny]

Originally Posted by Techno Duck

With the early temp gauge on my 924S, i would see the needle go slightly past the 3rd line before the fans kicked on.

As in the last line before the filled yellow box? Higher than I expected. How high does it normally get for you when you're not sitting idle in traffic? What would you consider the maximum "safe" value, or in other words how high does it need to get before I need to pull over and shut the engine off to avoid possible damage?

[Techno Duck]

Yup, the last line before the yellow box. Sitting in traffic on a relatively warm day i would see the temp climb up to slightly past the 3rd mark, fans kick on temp goes down to under the 2nd line. This repeats as long as im sitting in traffic.

I would shut down the car if you saw the needle reach the filled in yellow box. The start of the box is 105*C (221*F) and the end of the box is 120*C (248*F). 221*F is hot, but still okay.. anything over 225*F and its time to shut the car down and let it cool off in my opinion. For what its worth, i have an aftermarket gauge tapped into the upper radiator hose (So it sees similar temps to what the stock gauge see's), i have a visual alarm set at 225*F so i know its time to start easing up and letting the car cool off.

The stock fan switch kicks the fans on at 92*C roughly (temp taken at the top of the radiator), but take note the temp sensor for the gauge is located at the top of the cylinder head, right where the coolant exits the block into the radiator, so you will see marginally higher temps here.

This should be helpful to visualize what im saying..

[Mask of Destiny]

That indeed is a very helpful graphic. Thank you!

Drove it around some more after the rebleed and got it almost to the yellow box and the radiator was still cold. I ended up taking it back to the mechanic because I was out of time to fiddle with it myself. He replaced the thermostat and thermofan switch. He apparently drove it around for 25 minutes without issue and also let it idle until the fan came on and that worked fine too.

When I took it home, however, it got all the way between the 3rd line and the yellow box. Fortunately, a number of things lead me to believe this is an electrical issue with the guage rather than the engine getting that hot. The instrument light for the temp guage doesn't always work. On that drive home, the light suddenly started working and the guage instantly jumped from a hair past the 2nd line to the 3rd line. Later, when I turned the blower down a notch the needle jumped in the opposite direction (but not as far). When the mechanic tested it, it was daylight out so the headlights (and in turn all the instrument lights) were off which could explain why the guage worked fine for him. I guess it's time to go through and give the grounds a thorough cleaning.

Anyway, I'm going to try to drive it to work this morning and see how it goes. Wish me luck!

EDIT: Success! Despite the terrible stop and go traffic this morning it never got more than slightly past the 3rd line. Definitely time to clean the grounds.