Variable oil pressure...

[sailhog]

Ahoy all... MY engine has about 15 hours on it since the last oil change. Until recently, the oil pressure registered right around 45 psi at start, and then slowly ticked down to around 30 psi after an hour or so of run time. On the last couple of outings, the oil pressure registers at 60 psi at start and then slowly settles down to about 20 psi after an hour or so of run time.

I'm not sure if I'm remembering this correctly, but it seems that I had read on the forum that this wildly varying oil pressure could be caused by sludge in the crankcase. To remove much of it, you could add a quart of MMO to the crankcase during an oil change, followed by running the engine for a period of time, followed by a standard oil change (without MMO).

So three questions: Is this a legitimate remedy? If not, is there a remedy out there? Or is it really not a problem?

Any comments would be much appreciated.

Thanks to you all...

[jcwright]

When trying to figure out variable oil pressure after a rebuild I found a mechanical gauge helpful. Here is the description of the gauge in the MMI catalog:

Mechanical oil pressure gauge kit

This kit is intended to be used in the engine compartment to verify a cockpit gauge reading anytime there is a serious concern over oil pressure. The kit includes a mechanical oil pressure gauge, copper tubing and fittings to connect the gauge directly to the oil pressure port behind the flywheel housing. There is also a small needle valve in the kit to provide “snubbing” for very stable readings.

[Al Schober]

Agree to check things with a mechanical gauge. Electrical senders DO wear out, and guess what - they wear most in the spot on the sender where the pressure is most of the time. Most of these senders are carbon film units and the film wears down where the wiper spends time rubbing.

[joe_db]

FYI - I found Shell Rotella 15W40 to have less variation between hot and cold than the other oils I have tried. If you are changing oil anyway, give it a shot.