Expected oil pressure regulation IO-360

I am witnessing oil pressure variation from warm to hot that exceed the variation seen on other like engines around my airport.

IO-360-B1B
Looking at the range 130F/89psi to 210F/68psi @ 2500rpm (hot idle 48psi)

This engine only has 300hrs smoh but was pickled for 12 years before I got it. Within a year I had to externally reseal the case halves and replaced the front seal as all the gaskets started to fail after putting it in service. Vans standard oil cooler and new hoses were installed and the oil temperatures in summer normally run around 200F.
Looking for the most likely place to start. Oil cooler/Vernatherm, leaking oil relief seat, oil pump or ignore as normal operation?
Recently I have seen several post about the relief valve seat. Does anyone have a procedure beyond visual inspection? I have also seen a few post about the oil pump gasket failure yet I don?t see a gasket called out. The oil pump AD was done when it was pickled but was not run until 12 years later.

I would install a test guage and run up for a groundcheck just to be sure the pressure transducer and the guage were in agreement. That could be an easy fix.

Guessing you're not comfortable with the idle oil pressure. Yes? I've been in that boat. And yes, check your gauges first before anything else.

Those numbers really aren't too bad. You might increase the relief 5 psi and see where your idle ends up.

While you're adding washer(s) to the relief spring (assuming it's that type), you could inspect all the parts pretty easily. Pull the cover, spring, ball. Inspect the parts and the seat. You'll need a lot of light and a mirror to make a good visual on the seat. Make sure nothing caught or deposited there. I have lapped the seat before. Have to make a special tool, but it's not too hard. Use a spare steel relief ball, or one similar size welded to a 1/4" stub. Fit into an angle drill motor, dab on some valve grinding compound and go after it. I've also used a spherical stone to take deeper cuts since mine had some pitting. Use grease on the stone to capture the ground material. Then follow up with a Q tip soaked with oil or light grease to clean anything remaining.

Unfortunately, after chasing a lot of things I never solved the problem. I overhauled the engine and now the idle pressure is ~70.

DennisRhodes said:

I would install a test guage and run up for a groundcheck just to be sure the pressure transducer and the guage were in agreement. That could be an easy fix.

Click to expand...

Oil pressure was on a VDO gauge but last week I changed over to the better Kavlico sensor. The Kavlico reads a few pounds lower than my old VDO but the 30psi differential is seen with both. It would be nice to check the ABS pressure but right now I am looking more into why the regulation is so bad.


I guess my next step is inspecting the relief valve seat and possibly lapping it.

Slight oil bypass seat damage

At 9 o'clock there is a possible ridge but would this degree of damage really make a measurable difference in hot oil pressure?


https://drive.google.com/file/d/1KVtyJxD8rwvBSxJYGfZIPKuZ_a1iT2yS/view?usp=sharing