Bonton

Friends,

We're still experiencing 100 degree days in Austin. Ever since I've had the car (replaced old radiator with all aluminum 928 Motorsport one), I have listened for and heard the electric fans continue to pump air after shut-off.

Lately they have not remained on/come on upon shut off. What could be the problem? It is still hot as hell and I'd expect them to come on.

What should I check as I hear them during normal operation.



Thanks, Josh

Alan

What model year - can make all the difference...?

1) Make sure hood switch operates correctly - if not and the car thinks the hood is open this won't work

2) Check the switch on top of the intake - with the hood switch as if its closed - short together the switch terminals on the car wiring side - fans should come on... test the switch for continuity when hot (if no good replace).

Alan

dr bob

Josh--

Alan and I were typing at the same time...



As before, that switch on the top of the intake drives the fans on hot shutdown with heat soak.

1) Verify that the fans do in fact run with key off less than a couple minutes, withe hood closed and the two connections to that temp switch coupled together. If that doesn't cause them to run, you get to go deeper into the fan control diagnostics.

2) If the fans run with the wires connected, pull the switch out and do some kitchen testing with it. Connect an Ohm meter to it securely, and put the switch in the toaster oven with an oven thermometer. By the time the oven temp is at 200º for a bit, the switch should close (go to almost zero Ohms). If it doesn't, look for another switch.

---

We live at the top of a hill with more than a mile of uphill access road and driveway. On 100º days, and after that uphill run with the AC cranking to cool the black car, the fans might run on once in a very great while. The radiator temp tells me that it's a bit of extra work for the car going uphill at low speeds. On those days I pop the hood for a while after it's parked, so I get to listen for the fans at every drive home. They run so seldom that I don't really give it that much thought. I know they work, and let the system do its job when it needs to I guess.

Alan

Yep it dos have to be really hot - a hot day is not enough - you need long heat soak and high engine power for a while right before shutdown. If you recently improved your coolling system - that coiuld be why you don't see it anymore.

It doesn't always happen at 110F here in Phoenix after a >20 min drive at freeway speed... but.... YMMV... as Ed would say

Alan

Bonton

I hear you both: I just went out and saw it: The brass bodied unit with two leads coming off of it right?

So when you open the hood, the momentary switch which controls the engine bay light cuts out the fans but the thermal switch turn them on - correct?

The leads on the unit are clean the female spade perhaps not so much so I removed and replaced them and will see if it begins to work again.

Am I on the right track so far short of testing it/replacing it?

Thanks, Josh

dr bob

Josh--

Put a spring clamp on the hood switch so it stays in the hood-closed position. Take the two wire connectors off the switch (yes, the brass-looking one with the two wires attached) and connect the two wires together. The two female spade connectors will sort of interlock with each other if one is upside-down to its mate. Then start the car and immediately shut it off. The fans (both of them) should run at low speed. If it does, the wiring and controller are fine. Then do the trick with the switch in the toaster oven wired to the meter/continuity tester. If you walk the temp up slowly, you'll be able to see the switchover point on your thermometer.

Alan

Actually test it.. (cycle ignition on/of) pull off the connection to the switch and short the wires together - push down on the hood switch - fans should come on...

The temp switch makes them come on - UNLESS the hood is open. This is so the fans don't start up unexpectedly when you have your hands in there...

If this works and cycles with the hood switch (and the hood activates it) then the electrical side is OK except perhaps the temp switch - as Dr Bob indicated take it out and test it with an ohmmeter and a pot of boiling water - or an oven. All easy to do.

Alan

Randy V

It appears Bob & Al have become assimilated into the Collective.

MainePorsche

The Upper Echelon folks here always have been.

OTR18WHEELER

for what it's worth, it got to 100 F here today, While waiting in line for cheap $3.59/gal 93 oct gas, with the A/C cranked, my temp. light came on (first time ever), once I fueled and began driving , the temp wnt down, and 8 miles later when I got home, the temp was still pretty high, and the fan was runnning while at idle, but when I shut off the car (no temp light), the fan also stopped. I popped the hood, and went inside. I didnt blow a gasket, so no problems, right?.

Alan

Probably not - but it really shouldn't overheat at idle - I'd check the fan operation and see that you have enough coolant etc.

If you changed anything recently I'd check it...

Alan

dr bob

I have personal experience with water and that switch, failure following directly on the heels of a little engine cleaning with the hose. So I still suggest the slow-roast in the toaster oven for testing.

It's an easy recommendation -- I grabbed K's kitchen toaster oven when she replaced it cuz something spilled inside. Roasted beets urped red sugar syrup, which was then cauterized on the bottom pan. Pulled the pan, cauterized the sugar some more with a small torch, brushed off the ash, and good enough for casual garage duty. Heaven forbid it could go back where --food-- might get near it... Anyway, it's great for heating front hubs for wheel bearing fitment, stuff like that.

Tails

+1 to Alan's and dr bob's comments.

I have just machined the top off a failed temperature switch (after another 928S4 owner washed his engine.

The switch is a spring loaded fulcrum contact switch operated by expansion of and internal piece contained within the bottom of the switch.

The failure of the switch was caused by debris washed in with the water and lodged between the contacts of the switch. In some switches the two spade connectors embedded into the plastic like piece can turn with the brass body as the brass body has not been rolled tightly over this switch insert to form a water tight seal.

I cleaned up the switch mechanism and internals and tested the switch by hand and the resistance was nearly zero.

On closer study these switches are repairable by machining off the top rolled section of the body, machining up a cap piece and soldering the cap piece in place after cleaning up the switch mechanism. The temperature setting is via a dimpled former applying pressure to the bottom of the switch until the switch trips at 85 degrees C.

I attach some photographs of the switch for information (sorry about the quality).

Tails

I will try and get some better shots with my digital camera instead of my IPhone

Randy V

Use the macro setting on the phone - the little flower icon - for close up shots.