924Board.org

[ted von Kampen]

I think my temp sender gauge is bad. Anyone know what ohms a good one should read? Mine might be open. It has about 8 VDC on the bl/yel wire when switch is on. I think the other side is to go to ground but it doesn't work. Any comments or should I go get a new one?
Thanks

[ted von Kampen]

I used a potentiometer attached from the blue/yellow wire to ground. Turning the ignition on I adjusted the pot until dash temp gauge went all the way to the right (hot). I removed the pot and measured the ohms at that point. It was 32 ohms.

Then I reattached and readjusted till the dash gauge went to the left all the way but not buried. Ie- bottom of cold area. Again I removed and read ohms. this was 265 ohms. So a temp sender should read about the 265 when cold and if heated 32 ohms to work with this gauge.

Now my question is: where is the actual temp sender located? Not a temp switch but the variable resistance sender. At the back, just below the distributor and just in back of the WUR is a small pipe that had a sensor with two blade connections and also a sensor with two vacuum hoses. I think the latter is to allow the vacuum retard to work when the engine is heated. However, is the other 2 bladed sensor the temp guage sender?
I have found conflicting comments on the forum as to these. My two bladed sensor is open circuited so either it is a bad sensor or a switch. Any comments appreciated.

[ideola]

No. The coolant temp sender screws into the rear water flange, attached to the back of the head, underneath the ignition distributor. It is difficult (but not impossible) to access with the engine in situ. It screws into the rear water flange, but is difficult to reach because it's between the larger of the two heater hoses and the head. Here is a photo:


In this picture, you can't see the sensor itself, but you can see the blue/yellow wire that attaches to it (look on the far left side of the photo, about halfway down, you'll see the wire curving up and behind the heater hose).

To access, it may help to remove the coil. When installed, the CLT is basically in a horizontal orientation, with the connection end pointing toward the left side of the engine bay. It is a self-grounding style sensor, so it only has a single connection. The connector on the sensor itself is round and flat, but it uses a standard-sized female spade connector on the wiring harness (again, refer to above photo).
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erstwhile owner of just about every 924 variant ever made

[ted von Kampen]

Ideola- thanks for the information and photo. No wonder it is so hard to see. It may well be that the wire is just disconnected. I have a remote camera so I will try to view with that.

Just to reiterate, mine is a 1981 Porsche 924. It seems that a lot of things changed over the years. I just want to verify that your photo is valid for a 1981.
Thanks again,
Ted

[ted von Kampen]

Ideola - using your photo and information I found the sender buried just where you said it would be. Thanks a bunch. I will hookup and see if it works. There was not connection to it. It will be difficult to get to but maybe with the coil out it may be accessible. Do you have any idea what the two bladed sensor next to the vacuum switch is for?

I have a lot of things on this car that are disconnected or missng. At least I got the ignition working correctly. I hope that you can help me more in the future. Thanks again.
Ted

[ideola]

I honestly don't know what those two switches on the little hard pipe are for. One is a temp switch, and the other is a thermo valve, obviously tied in to the vac lines. I did a cursory search but could only find part numbers, not a description of their function. This will require some more digging.

Note for others who may encounter this thread: On some NAs, there is a third switch in the hard pipe. Here are the part numbers (for cross referencing and future research):
coolant temperature switch PN 047 131 851 D
thermo vacuum valve PN 058 131 851 A
acceleration enrichment temperature switch PN 047 131 851 D (I am theorizing that this last one is a US-only switch tied in with the Lambda system / frequency valve).
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erstwhile owner of just about every 924 variant ever made

[924RACR]

I recall that the thermo valve is in the vac feed line to the evap control valve... my suspicion is that it prevents the evap canister (which gathers the emissions from the gas tank into a carbon canister, then vents them back into the engine to burn off, reducing emissions, when the engine's under vacuum - closed throttle) from venting until the engine's warmed up.

I also seem to recall that the electrical temp switch in the pipe, at least on my S2 931, is tied in to the ignition computer to indicate a warmed-up engine, allowing different ignition mapping. Obviously not as sophisticated as a modern controller, rather than having a temp-dependent mapping it just switches between a cold/warm-up map and a warmed-up map...
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Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[ted von Kampen]

Ideola - I reconnected the temp gauge to the blue/yellow wire today and ran the engine. The temp gauge seems to work fine so thanks again for the help.

New question.. Heater valve. I found mine but the Bowden cable was not connected. I tried to move by hand but it seemed stuck. Is this a common service problem?

Also, were the 924's ever made with an external overflow tank light modern US cars? I ask because I ran it today and it filled the header expansion tank and then burped some coolant out the hose. Since this hose is outside the pressurized system I was wondering about an expansion tank. I have not "burped" the air out the coolant air bleed so that may be some of the problem.

[ideola]

RE: heater control valve, yes, it is common that they freeze. Usually when this happens, it's too late and they cannot be freed up, but it might still be worth trying to spray some penetrating oil to see if you can get it operational. BOTH of my OEM suppliers no longer carry this part. I have not checked with the dealer, nor have I checked to see if there is a generic/VW replacement.

RE: the coolant system, there is no overflow tank, only the expansion tank. What is the status of your cooling system?
- Coolant? (age and last changed)
- T-stat?
- Water pump?
- Pressure test?

The behavior you describe could be anything from insufficient coolant in the system, air in the system, blown head gasket, inoperable rad fan (leading to overheating), etc.
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erstwhile owner of just about every 924 variant ever made

[ted von Kampen]

Thanks for the suggestion on freeing up. I will try that. I saw that Pelican still has one listed.

As to the system. Water pump is old and was on the car when put in storage 15yr ago. Not leaking now but it might eventually. Head gasket replaced 15 yr ago and had been blown. Not run till now. Antifreeze probably 15 yr old but it does look good. Needs changing I am sure.
Fans do come on. This overflow came after some prolonged running in the garage while I did some other things. The expansion tank may be too full. I need to check further.

[924RACR]

OK, but you must burp it at the air bleed over the t-stat.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[ideola]

At this stage of the game, I would drain all of the coolant, flush the system at least twice, then replace the water pump (might as well do the timing belt while you're at it), refill with fresh mix, and properly bleed.
_________________
erstwhile owner of just about every 924 variant ever made