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Diagonosing a "hot" running 924S

 
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austinporsche  



Joined: 26 Apr 2018
Posts: 17
Location: Austin, TX

PostPosted: Mon Nov 05, 2018 9:28 am    Post subject: Diagonosing a "hot" running 924S Reply with quote

I have a 924S that I bought about a year ago on BAT.

Previous owner disclosed that the coolant temp gauge ran hot, but he said that it was a gauge or resistance issue (as the sensor is a single pole type and uses the body or the sensor-to-the-engine block as the ground).

The temperature reading seems to track positively pretty well to the outside temp.

at 40F, the temp reads about 60%

at 70F the temp reads about 75% (right below the edge of the red zone)

above 80F it is solidly in the red (above 90F, it is pegged in the red zome)

When the car is moving the temp will drop a bit from those positions.

Both fans will run once the car is warmed up (so not a fan temp sensor on the radiator issue, right?).

As I see it there are four things that could be wrong here:

1. Bad thermostat (is it possible that the thermostat never opens when the temp is 70F or below? I bought a replacement as they are cheap but getting to the circlip holding it into the thermostat body looks like a bit of a challenge to get to, ergo the post to see if there is something simpler I am missing)

2. Bad sensor

3. High resistance on either the positive or ground sensor-to-gauge paths

4. Bad gauge

Does this seem right? Could it also be a poor performing (clogged) radiator?


I was going to start with cheapest/easiest (the thermostat), but before I get going on it this week, wanted to see if there was an words or wisdom from those more familiar with these vehicles than me.

BTW, I have an infrared temperature gun so I can measure temps anywhere on the engine if that will help.


Last edited by austinporsche on Tue Nov 06, 2018 4:33 am; edited 1 time in total
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Paul  



Joined: 02 Nov 2002
Posts: 9349
Location: Southeast Wisconsin

PostPosted: Mon Nov 05, 2018 1:16 pm    Post subject: Reply with quote

Yes measure it at the thermostat housing just as the fans kick in.
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austinporsche  



Joined: 26 Apr 2018
Posts: 17
Location: Austin, TX

PostPosted: Tue Nov 06, 2018 4:23 am    Post subject: Reply with quote

OK, will do later today, then post it.

If I let the engine idle, at 75ish degrees F ambient, then the coolant in the block jacket should eventually get hot enough to open the thermostat, right? Assuming that this is why you want to know that temperature.
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Paul  



Joined: 02 Nov 2002
Posts: 9349
Location: Southeast Wisconsin

PostPosted: Tue Nov 06, 2018 1:29 pm    Post subject: Reply with quote

Interested at what temp the fans start and what the dash temp gauge reads vs your IR temp gauge.

Run the car until its warm then measure the temp when the fans turn on.
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White 87 924S "Ghost"
Silver 98 986 3.6l 320 HP "Frank N Stein"
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Polar Silver 02 996TT. "Turbo"
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austinporsche  



Joined: 26 Apr 2018
Posts: 17
Location: Austin, TX

PostPosted: Tue Nov 06, 2018 6:35 pm    Post subject: Reply with quote

OK, with the car completely warmed up and having been run 25ish miles at an ambient temperature of about 70F, the hottest part of the thermostat housing read between 175 and 181F with my infrared gun. (had to drive it somewhere, couldn't wait for it to warm up unto,the fans kicked in).

The plastic overflow tank read about 135F.

Does this mean the thermostat (and water pump and radiator) is ok?

Should I move on to sensor/wiring paths/gauge itself?

FYI, the block read about 200-205F and the exhaust manifold about 575F.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1013
Location: Washington DC area

PostPosted: Wed Nov 07, 2018 2:31 am    Post subject: Reply with quote

Those are all good numbers.
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Paul  



Joined: 02 Nov 2002
Posts: 9349
Location: Southeast Wisconsin

PostPosted: Wed Nov 07, 2018 4:19 am    Post subject: Reply with quote

When your IR gun said 181, what did the dash gauge indicate?
_________________
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
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austinporsche  



Joined: 26 Apr 2018
Posts: 17
Location: Austin, TX

PostPosted: Fri Nov 09, 2018 1:07 am    Post subject: Reply with quote

Sorry for belated reply. Email notifications of your responses got caught up in my spam filter.

When I measured the 181F at the thermostat housing, the indicator was right on the low end of the "red zone": at about the 3/4 or 75% max on the gauge. (BTW, checked calibration of my infrared reader and is is within a fraction of a degree up to 100C).

I would have guessed/expected that the gauge should have been closer to the 50%/midpoint of the gauge when the thermostat housing was around 180F (is 180F normal operating temperature for the coolant?).

Based on the readings at the thermostat housing for a fully warmed up engine, I am guessing that the thermostat itself is not the issue?

Thoughts on what my next steps should be?

The sensor on top of the intake manifold/block is easy yo get to.

I've had it out to clean/inspect (esp. as the body of the sensor is effectively the ground blade), but couldn't find on line what the resistance readings for the sensor should be at, say, 70F and 212F (boiling water).

If soneone knows that, then I can confirm or eliminate the sensor as the issue and move on to the wiring (including the ground path) and then the gauge itself.
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11356
Location: PacNW

PostPosted: Tue Nov 13, 2018 3:48 am    Post subject: Reply with quote

Bad grounds. Engine temp is fine.
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Fifty50Plus  



Joined: 28 Feb 2008
Posts: 1013
Location: Washington DC area

PostPosted: Tue Nov 13, 2018 10:23 am    Post subject: Reply with quote

Lookie who showed up
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1979 924 NA race car
1982 924 NA race car - Sold
1982 924 Turbo almost a PoS
1981 924 Turbo a real PoS, new engine
1982 924 Turbo nice body, blown engine
1972 911 E race car - going to Vintage
Various 944s to become IT-S race car
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16again2009  



Joined: 04 Dec 2014
Posts: 35
Location: tulsa, ok

PostPosted: Thu Nov 15, 2018 2:49 pm    Post subject: Reply with quote

Which ground was it?
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