924Board.org

[Brian L.]

Temperature gauge pegs in the red

After getting my 924 back on the road after sitting a number of years my temperature gauge
would read just below the 1/4 mark cruising at a constant 50 mph but in traffic it would go a little
past the halfway (5/8) before the radiator fan would turn on and it would get up to the 3/4 mark
and if I shut my car off with it at the 3/4 mark it would burp up some coolant soon afterwards.

So I have recently done the following, mostly due to reading post on this board.
Flushed my cooling system ( radiator looked clean inside prior to flush.
Replaced radiator fan switch with a lower temp one.
Replaced the thermostat (although old one seemed ok)
Cleaned all my ground locations (made my oil pressure read 3.5 bars instead of 1.5).

My temp. gauge now runs at the 1/4 mark consistently. No fluctuation up and down runs great I couldn’t be happier, until last Thursday when on my way home I see my gauge pegged all the way into the red. I pull over pop the hood. No steam, no coolant overflow, Take off the radiator cap coolant doesn’t overflow and the tank is full.

Now when I start the car(when cold) the temp. gauge gets to the 1/4 mark in less than half the normal time and then just keeps on rising at a steady rate (no jerking or jumping) until pegged all the way into the red.
After a couple of minutes in the red the fan kicks on for about 30 seconds.

The amount of time from when I start my car to when the fans come on is about the same as when my temp. gauge would run steady at the 1/4 mark before this problem.

I have rechecked everything. Temp. Sending unit, rad. Fan switch, ground to gauge, reflushed, checked sending unit resistance (65 ohms when full hot), checked sending unit wire resistance. I even put a meat thermometer in where the bleeder plug goes and got a nice even 180 degrees.

Is it then possible the temp. gauge itself is faulty?
Or a air pocket or blockage in the back of the head by the sending unit?

Any help much appreciated.
Brian
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1980 924 N.A. Monaco Blue owned since 1987
"Remember, sitting on your ass won't finish your project" -Puddins fab shop.

[augidog]

maybe a bad thermostat-even a new one could be bad off the start.
Did you bleed the system?
_________________
1978 924 95 mile daily driver.
Audi TB/POR174M/High Flow Cat/2.25" exhaust
I knew that positive thinking thing wouldn't work.

[924 driver]

change the cap ?

_________________
Peter
1979 924 na

[Brian L.]

Audiodog I had already check the thermostat. Placed it in a pan with my wife’s candy thermometer and both the old and new
One seems to work just fine.

924driver, the radiator cap is a good suggestion because I think my old one is suspect. I put a new one on today and bled
the system again but still have the same old problem!

I have cleaned all the connections to my cluster gauges and I have added a extra ground strap from the battery to the
Chassis and a extra strap from the chassis to the engine block to no avail.

I remember someone saying that they had overheating problems due to a air pocket in their cooling system that they had trouble
Getting it out.

I getting close to the point of removing my clock and replacing it with a VDO temp. gauge, although I would like to put a oil temp gauge there.
_________________
1980 924 N.A. Monaco Blue owned since 1987
"Remember, sitting on your ass won't finish your project" -Puddins fab shop.

[Ozzie]

Temp guage or sender.
Sounds like the guage after the checks you done.
_________________
Porsche 924 1984 (UK import) NA
Its AUTO and its BLACK
Montego Black on black/red
Engineer of Electro/Mechanical Systems Maintenance