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Oil cooler and Thermostat trouble shooting

 
Old 05-20-2010, 01:21 PM
  #1  
vespam5
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Default Oil cooler and Thermostat trouble shooting

Hello fellow 964 owners and enthusiasts.

I am having some issues with my 1992 C2 which I just recently picked up and I was hoping for some expertise from the community. Input from anyone who knows the cooling system well would be much appreciated.

My car has recently started running warmer than I'd like. From what I gather from a lot of searching here on the forums is that the oil temperature should be between the 8 and 9 O'clock positions under normal driving. My car has been there since I purchased it but the last couple of days I noticed it creeping closer to the 10 or 10:15 position on my commutes to work. Temperature is still quite a way from the red zone but since I'm used to cooler temperatures, this concerned me.

When I got home I referred to my two new Bentley manuals (which aren't nearly as good for Porsche as they are for BMW) and learned what I could from the limited information they provide on the system.

I first checked out the oil cooler fan electronics. Fuse#2 and relays r04 and r014 to make sure everything was ok and they were. I then bypassed the relays to operate both slow and fast speeds of the oil cooler fan and everything worked fine but the Fans just wouldn't come on by themselves when car was fully warm.

After checking the cooling electrics I made a important observation. While I had the car running with the oil temp slowly creeping towards 10 o'clock position again the oil cooler fan should have come on by now but did not. Since I had the inner fender lining out I rested my hand on the oil cooler and it was cold to the touch. At this point the oil thermostat should have opened and allowed oil to the cooler. It became obvious I had a bad thermostat. I felt the oil lines along the side of the car and they too were cool all the way back to the thermostat housing.

I placed an order for the thermostat but really needed the car to be operational for work so I took the thermostat out and then re-installed the o-ring, cap, and snap ring. I figured that oil would definitely get to the cooler if there was no thermostat there. I started the car, checked for leaks, and went for a test drive. The oil temperature was definitely cooler and didn't pass the 9:15 ish mark but when I went to touch the oil cooler again i was surprised to see that it was still cold to the touch.

So now I am assuming that the thermostat isn't simply a on/off switch for the supply line to the cooler, but also directs the oil specifically to the "hot" line. Without the thermostat in place the "hot" line is not pressurized and oil cooler system does not work as it should? It hard to figure out the exact plumbing of the system without a reference.

Car is parked until thermostat arrives and taking the Ducati to work (hurry up Pelican)!
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Old 05-20-2010, 01:34 PM
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elbeee964
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Originally Posted by vespam5 View Post
So now I am assuming that the thermostat isn't simply a on/off switch for the supply line to the cooler, but also directs the oil specifically to the "hot" line.
Nope, it's pretty much just that: an on(warm)/off(cool) bypass valve that should - when the oil gets warm enough - shunt oil to the front oil cooler before its return to the oil tank.
Yours sounds as if it's in permanent 'off' status at the moment. Sorry.

When all's working well, the oil lines' passage to & from the front cooler will leave the front right side fender (above the wheel) warmer to the touch than its left side counterpart. A warm right fender = an operating thermostat.
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Old 05-20-2010, 01:41 PM
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So you are saying that the thermostat "removed" is the same as the thermostat "open" for cooling purposes?
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Old 05-20-2010, 01:48 PM
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Are you referring to whether taking out the thermostat's guts (with the thermostat body still in place) make it shunt oil full-time to the front cooler?
Hmmm... I don't know that one.

Anyone, care to field this?
Bueller? ...Bueller?

No, at the moment I have the entire thermostat/spring out of the housing. I obviously re-installed the oring/cap/snap ring so oil doesn't BP out when I run the engine.
Yup. That's what I was referring to.
I'm still ignorant to the answer. Sorry.
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Old 05-20-2010, 01:53 PM
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No, at the moment I have the entire thermostat/spring out of the housing. I obviously re-installed the oring/cap/snap ring so oil doesn't BP out when I run the engine.
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Old 05-20-2010, 03:30 PM
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The thermostat diverts the oil flow. Without thermostat internals oil will flow to the least resistance. Through the cooler is not the path of least resistance, but a little flow will push through the cooler and you saw the results of that additional cooling. If the car is your only means of getting around, I'd keep driving it but watch the temp closely, and get the thermostat back together again once parts arrive.
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Old 05-20-2010, 03:49 PM
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I recently went through exactly the same situation. I ended up replacing both the oil cooler ballast resistor and thermostat insert.

10 o'clock oil temps - oil cooler fan/thermostat (fixed)

I reluctantly had to drive the car a couple times until I fixed the problem...saw temps close to 10, but with easy driving, low revs, heater on high and tail extended, I was able to drive only seeing temps at around 9:15 or so. The less aggressive you drive the less heat is built up in the system.

I like your experiment (driving without the thermo insert), I was wondering the same thing when I went through this??

Do you have extra parts for when you reattach the sils? Be careful

sill cover - parts laid out for all to see

Also, welcome to Rennlist!

P.S. One question. When I pulled my thermo insert, I only lost a quart of oil. I was prepared (and many said) to lose the whole contents of the tank. I'm wondering what's normal?
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Old 05-20-2010, 05:14 PM
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Doesnt most of the hot air from the heater get shot out the left rear tire area when its off? I dont think turning the heater on high would really be much help.
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Old 05-20-2010, 05:18 PM
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Mojorizing, I believe you are 100% correct and that was my theory are well.

911jetta, I will be installing the new thermostat tomorrow and if the problem does not go away completely I'll look into other issues. Right now the fans are not coming on but I'm pretty sure it's because the cooler is cold.

Of course I broke every single clip when removing the side panel but I ordered plenty of extras along with the rest of my parts I am expecting.

Thanks for the welcome, I'll be posting pictures of my car soon, as soon as I get a day off to spend with her!
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Old 05-22-2010, 01:45 PM
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Just a quick follow up. I replaced the thermostat and o ring with new ones and the car is back to nice cool operating temperatures. Oil is now getting to the cooler as it should and the fans are coming on although it's going to take some work to get the oil warm enough for the fan to need to come on!

So to answer my own original question, yes the thermostat must be in place for the oil cooler to get pressurized oil.
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