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> Oil Pressure Funkiness... -6 Conversion
roblav1
post Jul 6 2021, 02:27 PM
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Getting some funky oil pressure readings, never seen this before.
930/02 engine, fully rebuilt.
Oil pressure sender matches the 911 gauge.
Wiring is direct from sender to gauge.
Ben's oil tank with stock 914-6 plumbing from tank to oil cooler.
12 quarts went in the system (external cooler up front) and oil level reads ok.

Anyway, when cranking via battery, cold oil pressure reads almost 100 psi. Ok, seen that before.

After the engine starts, at cold idle, oil pressure reads about 15 psi.

Cold pressure is around 30 psi at about 3000 rpm. Not good.

Why? Why good pressure at cranking then terrible pressure while running?

Does this sound like a collapsing oil tube?

Oil pump seal failure?

Broken oil pump shaft?

Or just a bad sender?

I think it's time to manually measure the oil pressure.

This engine is way too valuable to ruin. This is my 6th 911 engine rebuild.

Thanks for any insights.
Rob
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lesorubcheek
post Jul 6 2021, 03:40 PM
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My guess would be a sticking pressure valve piston. This could explain the 100 psi when cranking (stuck closed) and low pressure when running (stuck open a bit too far after pressure builds and it finally opens). Again, just a guess based on the symptoms.

Dan
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mepstein
post Jul 6 2021, 04:16 PM
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Oil lines going to the right place?
It is easy to check manually with an extension hose from flaps and a pressure gauge.
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roblav1
post Jul 6 2021, 05:30 PM
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This 1976 930/02 engine was supposed to have the oil bypass mod done at the factory. It does have the aluminum 4 rib oil pump as on the SC. I did not validate the correct relief valve piston assembly during the build. Probably a bad assumption. Time to check it. Thanks for the insights.
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mepstein
post Jul 6 2021, 05:52 PM
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I just put a euro carrera engine up for sale on pelican. If you continue to have trouble, I can get you in touch with Fred Apgar. The man knows Porsche engines like few others. He and Peter Dawe are my go-to for engine info. He just called me last night to chat.
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roblav1
post Jul 6 2021, 06:25 PM
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Thanks Mark. Small world. I met Fred at Hershey in 2019... he bought the CIS injection off this engine. I may still have his number.
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mepstein
post Jul 6 2021, 06:42 PM
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QUOTE(roblav1 @ Jul 6 2021, 08:25 PM) *

Thanks Mark. Small world. I met Fred at Hershey in 2019... he bought the CIS injection off this engine. I may still have his number.


He said Peter has built 3000 engines to his 2000 but he sure knows a lot and is willing to help.
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mb911
post Jul 7 2021, 05:38 AM
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10 psi per 1000rpm is perfectly normal. Cold my engine about puts out big numbers then as it warms its about 10 psi per.
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roblav1
post Jul 7 2021, 08:14 AM
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Concur Ben. 10psi per 1000rpm while hot is normal. Mine is while cold.
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mb911
post Jul 7 2021, 11:25 AM
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QUOTE(roblav1 @ Jul 7 2021, 06:14 AM) *

Concur Ben. 10psi per 1000rpm while hot is normal. Mine is while cold.



Verify manually then my 1st stop would be bypasses, then cam line restrictiors .
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mb911
post Jul 7 2021, 11:25 AM
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Then lastly bearing clearances. And also make sure no pinched feed lines
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roblav1
post Jul 7 2021, 06:26 PM
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Ok... chalk this one up to dumbsh**. I was being cautious by not bringing the engine up to operating temp with low oil pressure. So oil level was not really validated. I stuck a long welding rod down the tank and saw little oil... so I added 3 quarts, and Voila! Oil pressure! It's now over the 10psi per 1000rpm hot benchmark. Sorry for false alarm and thanks again for the insights. Now time to get the carbs tuned.
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Justinp71
post Jul 7 2021, 10:05 PM
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QUOTE(mb911 @ Jul 7 2021, 04:38 AM) *

10 psi per 1000rpm is perfectly normal. Cold my engine about puts out big numbers then as it warms its about 10 psi per.


What's your max reading? Mine is typically 4bar, 60psi stays there from 4k up to 7k... I think that is normal?
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mb911
post Jul 8 2021, 05:27 AM
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So it holds 15 qts? Wow that's a big system.
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9146GUY
post Jul 8 2021, 06:17 AM
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Not really a big system. Oil lines and coolers take more oil than one would think.

Our old race cars with -16 oil lines and big oil tank took almost 24 qts to fill the system.

I went through the same issue with the mule when I first got it from overseas. The fresh engine had sat for many years and the relief valves were the culprit for the same issues as described.
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