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low oil pressure

2009-04-19 16:48:47

low oil pressure

I own a 1960 Cessna 172A with a continental 0-300C engine. The oil pressure has always ran low, but within the bottom end of the limits. We live in Idaho and the field elevation is 4900 feet, we have been told that to correct for this problem to shim under the pressure relief valve spring. Is this a good idea? I have looked through the overhaul manual and have found no reference to doing this or have i found a TCM SB that talks about doing this. Whats anyones thoughts on the shimming idea?

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2009-04-20 04:58:26

Re: low oil pressure

Hello Doug;

Since you indicated that the oil pressure has always run low, I would guess that it wasn't properly set (shimmed) in the first place. As long as you have normal oil temperatures and no sign of abnormal wear or oil consumption, etc., I would think it would be OK to adjust it that way. My Lycoming powered 172 has a fitting under the oil pump in the engine accessory case with a locking bolt that you can adjust the oil pressure with, so Lycoming allows you to adjust the oil pressure.

Just my thoughts.

Jon

jplaxton00: jplaxton00; 186 Posts

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2009-04-21 00:34:39

Re: low oil pressure

I would check the oil pressure gauge for accuracy. You can tee a known good pressure gauge into the engine oil pressure sense line. check at the low end of the scale and the upper end.
Some Lycoming engines have an oil pressure relief device mounted on the engine case above the right rear cylinder. Washers can be added or removed to adjust the oil presssure.