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Can a faulty oil thermostat cause extreme oil pressure?

I have a shop telling me that my oil thermostat was binding and not working correctly, and this caused excessive pressure in the engine. Enough pressure to cause seals in the engine to leak (cam housing seals). Also, added pressure into my oil cooler? The engine has 500 miles on it after a complete rebuild. Of course they didn't check the oil thermostat when the cases wear apart - that seems questionable to me - but he is confident that it is not a typical part of a rebuild (at this shop i guess.. dang).

Is this even possible? Does a faulty oil thermostat create this kind of pressure? I was not even seeing excessive heat - nothing over 230 (which is high for a new engine I know).

Thanks
Old 10-05-2017, 10:28 PM
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Read this thread.
Ultimate Oil Pressure Relief Valve Thread

Have to be some pretty high pressures to make the engine leak.
Maybe provide a link to your other thread in the engine rebuilding section.
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Last edited by timmy2; 10-05-2017 at 10:41 PM..
Old 10-05-2017, 10:39 PM
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Quote:
Originally Posted by timmy2 View Post
Read this thread.
Ultimate Oil Pressure Relief Valve Thread

Have to be some pretty high pressures to make the engine leak.
Maybe provide a link to your other thread in the engine rebuilding section.


What a fantastic thread, thank you for bringing it to my attention.
Old 10-05-2017, 11:27 PM
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Just knowing how high the pressures get when the oil is cold leads me to believe the thermostat story for your leaks is bunkus. The bypass should kick in if oil pressures go high.
In your other thread you mention not noticing high oil pressures.
The leaks are more likely assembly workmanship or poor quality gaskets.

For others to read:
Shop Rebuilt 2.7 - Issues. Opinions please.
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Old 10-05-2017, 11:58 PM
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So what does your gauge read?
Old 10-06-2017, 05:31 AM
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Since the thermostat opens when the temps rise, wouldn't the problem show up when the engine is cold and the pressure is higher?
Old 10-06-2017, 06:09 AM
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The thermostat on the engine directs oil from the pressure side of the oil pump either through the engine mounted cooler before hitting the main oil galleys, or bypasses it and sends the oil directly to the mail oil galleys. Unless there is a blockage in one of these two places (which would separately be a problem), I don't see how a non-functioning thermostat can cause a high oil pressure condition in the engine.

From the comments in the OP's other thread in the Engine Rebuilding forum, it makes me wonder if there is a misconception here. A thermostat stuck in the "hot" position would send cold, thick engine oil to the engine-mounted cooler before the engine is warmed up. Oil pressure is naturally higher when the engine is cold, and this pressure can be too high for the cooler and blow out the cooler in some cases, causing it to leak. But sending cold oil through the cooler does not raise the overall oil pressure in the engine.

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Old 10-06-2017, 06:45 AM
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Quote:
Originally Posted by stownsen914 View Post
The thermostat on the engine directs oil from the pressure side of the oil pump either through the engine mounted cooler before hitting the main oil galleys, or bypasses it and sends the oil directly to the mail oil galleys. Unless there is a blockage in one of these two places (which would separately be a problem), I don't see how a non-functioning thermostat can cause a high oil pressure condition in the engine.

From the comments in the OP's other thread in the Engine Rebuilding forum, it makes me wonder if there is a misconception here. A thermostat stuck in the "hot" position would send cold, thick engine oil to the engine-mounted cooler before the engine is warmed up. Oil pressure is naturally higher when the engine is cold, and this pressure can be too high for the cooler and blow out the cooler in some cases, causing it to leak. But sending cold oil through the cooler does not raise the overall oil pressure in the engine.

Scott

I am getting conflicting information from the builder. Yes he has informed me the pressure caused a leak in my oil cooler, I have replaced the oil cooler. Once the oil cooler and thermostat where replaced they noticed the seal leakage after letting the car run for half an hour (which also seems a bit excessive but I've never built a 911 engine.)

Even though I'm almost certain my original cooler was leaking before the engine build. My question really is weather the high pressure (that would be cool oil) could result in "boiling" and if that could cause pressure through the heads to create a leak through the seals.

Thanks all.
Old 10-06-2017, 07:51 AM
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A malfunctioning thermostat on the motor really can't cause high oil pressure based on 3 facts:

1) The thermostat has a sliding portion, that directs oil back to the motor or to the thermostat. If you have it in your hand you can see it. That oil is going one of two directions, there is no option to have it "go nowhere" and raise oil pressure...
2) If that fails, the oil pressure relief valve kicks in as a safety at 75 psi
3) If that fails, the emergency oil relief valve kicks in (100 psi? No idea)...

Folks have had oil lines 100% crushed going to the front cooler, and no issues with high oil pressure (though it did overheat)...

I am not a pro, hopefully the pros chime in...

Your oil cooler, could fail at any time if it were old... they just leak...

Did you by any chance go from dino oil to synthetic? I did that before, and my car leaked EVERYWHERE...

Last edited by bpu699; 10-06-2017 at 08:41 AM..
Old 10-06-2017, 08:38 AM
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Quote:
Originally Posted by timmy2 View Post
Just knowing how high the pressures get when the oil is cold leads me to believe the thermostat story for your leaks is bunkus. The bypass should kick in if oil pressures go high.
+1 bunkus AND horse-pucky.

If your auxiliary thermo was welded shut your symptom would be overheat with a larger mid-year engine.

Early 911's had no auxiliary cooler. No trombone, nuttin.
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Old 10-06-2017, 02:08 PM
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From the other thread (in Eng Rebuilding forum) from the OP, I'd understood that he was being told the thermostat on the engine was the one in question. Not the auxiliary thermostat controlling flow to the fender mounted oil cooler. Though I think the story is the same either way - I don't see how a stuck thermostat (either one) can cause a high pressure condition in the engine.

Last edited by stownsen914; 10-07-2017 at 05:37 AM..
Old 10-07-2017, 05:35 AM
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Quote:
Originally Posted by stownsen914 View Post
From the other thread (in Eng Rebuilding forum) from the OP, I'd understood that he was being told the thermostat on the engine was the one in question. Not the auxiliary thermostat controlling flow to the fender mounted oil cooler. Though I think the story is the same either way - I don't see how a stuck thermostat (either one) can cause a high pressure condition in the engine.
Thanks for that. (I now see bpu699's post on the engine thermo)

I have seen a nice oiling diagram that shows the routing and parts. I'll see if I can find that. I don't know enough about the engine thermo to speak on it.
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Old 10-07-2017, 07:30 AM
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Here it is

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Old 10-07-2017, 07:32 AM
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Yes the thermostat on the engine. Great diagram, thanks!
Drive by the shop and car still sitting without engine installed so next week I'll have to follow up.
Old 10-07-2017, 12:35 PM
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Quote:
Originally Posted by Bob Kontak View Post
Here it is


Such a fantastic diagram, exactly what I was after. In the alleged scenario the thermostat is stuck in the "hot" position letting cool oil into the oil cooler causing a high pressure scenario. Even if this resulted in a block in the oil cooler, it seems as though the relief valve would divert to the crankcase. So, the engine would have to be creating pressure from the crankcase up through the cam housing for his explanation to make sense. I've hired a donkey to build my engine folks. ****.
Old 10-07-2017, 12:50 PM
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sub..here one more for ya..
Old 10-07-2017, 12:52 PM
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Nice, Proporsche.

It appears there are two pressure relief mechanisms. The Pressure Relief Valve and the Safety Valve. That's a lot of German engineered insurance against excess pressure.

Here is my wild ass guess which goes back to post #4 where Timmy2 said it may be material/workmanship. I think your cooler casting is cracked.

Cooler seals do not leak as a rule but if a cooler has received trauma (like I "practiced" and dropped the weight of the engine on it) it will crack and it's very hard to see. Hairline fracture. Oil warms up, engine thermo opens, there you go.
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Old 10-07-2017, 01:12 PM
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Bob..there is a possible problem .If the boys (at the rebuild place )switched the oil press relieve valves i could imagine some kind of problems...basically i would not go back to them..simple as that

Ivan
Old 10-07-2017, 01:22 PM
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Originally Posted by proporsche View Post
Bob..there is a possible problem .If the boys (at the rebuild place )switched the oil press relieve valves i could imagine some kind of problems...basically i would not go back to them..simple as that

Ivan
Something is definitely wrong.

I do see the safety valve and pressure relief valve have a huge pressure engagement difference from your diagram.

My comment on the cracked cooler is simply based on my experience. And qualified as a wild ass guess.
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Old 10-07-2017, 01:41 PM
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Quote:
Originally Posted by submerge View Post
I have a shop telling me that my oil thermostat was binding and not working correctly, and this caused excessive pressure in the engine. Enough pressure to cause seals in the engine to leak (cam housing seals). Also, added pressure into my oil cooler? The engine has 500 miles on it after a complete rebuild. Of course they didn't check the oil thermostat when the cases wear apart - that seems questionable to me - but he is confident that it is not a typical part of a rebuild (at this shop i guess.. dang).

Is this even possible? Does a faulty oil thermostat create this kind of pressure? I was not even seeing excessive heat - nothing over 230 (which is high for a new engine I know).

Thanks
What was that EXCESSIVE pressure? RPM dependent or not?
Old 10-07-2017, 02:06 PM
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