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[Coolbri1191]

I've had this problem for way too long.

Both fans come on at the same time at a little passed the 2nd middle mark. But, the temperature continues to rise until almost the 3rd mark. Never higher ever since I had my head gasket done last summer.

Once the fans kick on, they never shut off. When the car is turned off, both fans continue to run in low speed for about a minute (unless my key is in the on position, then it's high speed), THEN they shut off.

I currently have a low temperature wahler thermoswitch installed, and a new 190? stock genuine thermostat that the shop installed.

I have repeatedly bled out the cooling system and I still don't think all the air bubbles are gone. This problem was also present before the head gasket.

What are my options? Thank you for your help.
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

The problem seems to be in your thermo-fan switch and thermostat combination.

The fans only need to come on when the thermostat opens up to cool off the hot coolant coming out of the engine. But with your combination, the fans are running long before they are needed, and continue to stay on because they think the engine is too hot. Meanwhile the thermostat knows all is well and continues to heat the coolant more.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Coolbri1191]

I have the original behr thermoswitch in my glove box, I can't remember if it was bad or not.

But should I put that one in and see if it helps?


Also when I had the other 160 thermostat installed it did the same thing; fans came on, but just a little earlier. Still never shut off.
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

While it is normal for the fans to occasionally stay on awhile after the car is turned off, it shouldn't happen every time.

If you had the same issue with a 160 degree thermostat, then it would appear that your thermo-fan switch is faulty.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Coolbri1191]

They continue to run when the car is off, only if the fans kick on while I'm driving. Or if I shut it off right before the half way mark, they'll come on.

The wahler thermoswitch was new in august 2010.

It would be worth noting, that when I was in lake havasu last summer (see this thread: Am I Looking at a Possible Rebuilt Head?), that at one point since it was so hot, that after driving around town and coming home, one of the fans (not both) continued to run for almost 30 minutes in low speed after the car was off. That would be the relay, right?


Anyways, I do agree with you that having a low temp thermoswitch and a stock thermostat is dumb, and probably the reason they kick on and stay on. I just can't understand why a new thermoswitch would go bad.
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

It's entirely possible that your relay is bad, all you need to do is this:

Drive the car until you know that the fan will remain on when you shut the car down.

With the engine off and fan running, unplug the thermo-fan switch.

If the fan stays on, the relay is bad. If it goes off, the thermo-fan switch is bad.

[Coolbri1191]

Unplug both terminals? Or just one?

And it's best to reach it from the top, right?
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

I believe unplugging either wire will work.

I don't think you can reach it from the top, even with air box removed.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Paul]

The coolant flows into the water pump from the radiator then goes through the block/head and exits on the head (where the bleeder is). Backwards of what most people believe.

So if the water from the radiator has been cooled by the thermo switch/fans to a temperature lower than the thermostat in the water pump, it delays the opening of the thermostat in the water pump resulting in the temperature of the cylinder head rising even after the fans start.

A long post for me....
_________________
White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
White 01 986 "Christine"
Polar Silver 02 996TT. "Turbo"
Owned and repaired 924s since 1977
Porsche: It's not driving, it's therapy.

[Coolbri1191]

I've been busy with work the passed couple days, so I just got to do what edredas said.

I got home today and the fans were running, so I shut off the car and put it back in the 'ON' position to put them on high speed, and as soon as I unplugged the brown wire with the white stripe one fan turned off, then a second later the other fan shut off.

I also did this when the car was completely off and realized that only one fan would run in low speed(not both like I thought), but I got the same result; the fan shut off right away.


But I'm starting to think that it's just a bad combination of the stock thermostat and low temp thermoswitch like edredas and Paul originally said. But that's why I asked why they wouldn't cycle like normal fans when I had the low temp thermostat installed..?


Anyways, should I just put the old original thermoswitch in? Could it possibly leak?
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

Where on the temp gauge does the fans come on when driving?
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Coolbri1191]

It goes in stages lol
A hair passed the half way mark,
relay clicks for fans and temperature goes up with the 'click' a little due to fans coming on,
temperature goes down to the middle of the half way mark,
then continues to climb right before the 3rd mark and stays there.

I can post a video if you want I guess... it would have to be tomorrow.
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[edredas]

Sounds like you could have air in your cooling system.

When driving, the temp should always run steady just shy of the second mark.
_________________
'84 944 -White, Brown interior
'84 944 -Red, Automatic
'86 944 -Garnet, Fully loaded, Koni suspension
'87 924S -Red, 300hp 951 swap
'87 924S -Red, Project Car
'88 924S -Red, Daily Driver

[Coolbri1191]

I've repeatedly tried getting the air out of the system, but it is not pressurizing. I can tell, because the top hose isn't as firm as it should be. Also, the cap is BRAND new. The cap that was on it before, was new (from Autozone and up to OEM specs) for about 9 months, then the shop put an OEM brand new one on too, because they said the autozone one was only holding 8psi.
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)

[Coolbri1191]

Found the original box of the Wahler thermofan switch.

Two sets of numbers were on it:
802 54067 087

823 959 481 75

I also looked up the UPC code, and tried to find out what temperature thermofan switch it was. After some digging around it turns out this is a 75-70C thermoswitch, meaning it kicks the fans on at 160F... and I have the stock 190F thermostat currently installed.. sigh. Didn't think it would be the lowest temp thermoswitch available.. Think I might've found my solution.


Should I reuse the original thermoswitch or order a new one?
_________________
Guards Red 1987 Porsche 924S (Automatic)
2001 Ford Explorer Sport (DD)