High Oil Pressure - Only at Idle

[windsaloft]

So what gives -- all is normal at full throttle (3200 rpm) to low cruise (2200 rpm), but back at engine cool idle (900-100 rpm) the oil pressure goes from its normal steady state 75-80 psi to pegged on the high pressure side. Yes, at idle, reduced power, oil pressure pegs.

Westerbeke 21 hp 2555 hours -- real transom soots, think that #3 cyl has reduced and reducing compression --- but, that is another (and posted) issue under "how long does she have, doc" --

What are causes of high oil pressure at idle, not seen at normal operating speeds?

Thanks.........

[GordMay]

High oil pressure is not generally a concern, but if pressure suddenly increases (other than at a cold start), there may be a problem with the oil pump pressure regulator (pressure relief valve).
This vents excess oil back to the sump, when the maximum allowable pressure is reached, to prevent erosion damage to the bearings etc.
I'm not certain why this would consistently occur only at idle, though.

[NCboatrx]

I would use a manual oil pressure gauge to check the readings of your electric one. It is possible that you may find something simple like a faulty connection or broken insulation when you do this. If this is so the repair will be simple.

Also, check your injectors and valve clearances. This and some fresh oil and oil filter may just help the smoke situation.

[S&S]

Bad sender, bad gauge, maybe a clogged oil filter(shows a resiriction until the bypass opens up). I'd say change the oil and filter and if it's still doing it try putting a mechanical gauge where the sender goes. IIRC, low voltage to the gauge would show as low, not high pressure.

[GordMay]

This doesn’t sound like an electrical (bad sender or gauge) problem to me.
I’d follow the advice to change oil & filtre, hoping for a change.

As S&S indicated, a Low supply Voltage would equate to a High Sender Resistance value; which would produce a Lower Pressure Indication.

FWIW, see “Basic Engine Gauge Theory & Testing “
➥ http://www.cruisersforum.com/forums/...sting-645.html

And the accompanying Graphics:
➥ http://www.cruisersforum.com/gallery...=500&userid=79
➥ http://www.cruisersforum.com/gallery...=500&userid=79
➥ http://www.cruisersforum.com/gallery...=500&userid=79

[windsaloft]

Deduction - oil and filter change addresses this. Oil only 4 months old and 56 hours -- which tells you the amount of sooting in the oil due to that bad rear cylinder that is low compression and apparently getting worse. Wish cylinder rebuilds on diesels were as easy as on recip aircraft engines! Take off the old, bolt on the new, presto chango!

[Chief Engineer]

Is there an adjustable Pressure regulator on these engines?

[doug86]

Originally Posted by windsaloft

So what gives -- all is normal at full throttle (3200 rpm) to low cruise (2200 rpm), but back at engine cool idle (900-100 rpm) the oil pressure goes from its normal steady state 75-80 psi to pegged on the high pressure side.

75-80 psi? That sounds really high for a small engine like that. Most smaller Westerbekes run around 40psi, and the manuals I checked say normal op range is 30-60 psi.

here is link to all the westerbeke manuals.

westerbeke, marine generators, engines, Official Site

I agree with others who say confirm these readings with a mechanical gauge before proceeding further, as something sounds fishy, and if it's an electrical gremlin, it should be easy to remedy.

[Dockhead]

That sounds very fishy to me. The volume of oil supplied by the pump obviously goes up with engine speed. There is no natural reason why oil pressure should increase at idle. The oil pump would not be capable of supplying 80psi of oil pressure at idle without a clog somewhere. The pressure relief valve will not be operating at idle.

Something is clogged, or there is some weird electrical/gauge problem.

I would start with the mechanical gauge to eliminate gauge problems, as others have suggested. If the mechanical gauge confirms the weird oil pressure, then this would be another reason why it's getting about time to tear that engine down.

[David M]

I would be willing to bet it is a false sensor reading and not actual high oil pressure. A slower turning oil pump is not going to increase the oil pressure....it's just the opposite.

[perchance]

I believe the standard test is to ground the sender wire. This will cause the guage to pin. Sounds like it is the sender if it is pinning the guage at idle.