Oil pressure drops then backfire/valve tap etc

[navcon@cfl.rr.com]

Have a 2005 Volvo Penta OSE-3 with 180 hours. When running, the oil pressure gradually drops from 60 to 25 over an hour or so. If running hard (4000 RPM for extended period of time), eventually get a backfire - easing back seems to fix it but recently when coming off plane the pressure dropped to below 20 and heard valve tapping and engine ran rough - started every 15 minutes after when docked and pressure gradually climbed back. What gives?

 

[jtybt]

Re: Oil pressure drops then backfire/valve tap etc

What weight oil do you have.

There are a lot of scary thing that can happen when oil pressure drops. 20 or 25 PSI isn't dropping...especially if engine is hot and throttle is backed off.

 

[Rob_NC]

Re: Oil pressure drops then backfire/valve tap etc

What weight oil do you have.

There are a lot of scary thing that can happen when oil pressure drops. 20 or 25 PSI isn't dropping...especially if engine is hot and throttle is backed off.

..booom...$$$$$...

 

[mla2ofus]

Re: Oil pressure drops then backfire/valve tap etc

I think you're developing a cam bearing problem. When the block gets warmed up good, it and the cam brgs expand dumping too much oil out thru them. The tapping is the lifters starving for oil.
JMHO,
Mike

 

[Don S]

Re: Oil pressure drops then backfire/valve tap etc

Check your oil level. After it sets overnight. Pull the dipstick, wipe it off and redip it. Bet it's overfull and you are checking it incorrectly.
With the level too high, the crankshaft hit the oil and aireates it. The air causes the lifters to rattle because the air compresses where straight oil does not.

 

[Bifflefan]

Re: Oil pressure drops then backfire/valve tap etc

yea it sonds like a bearing problem. the back fire is the valves not opening correctly do to low oil psi.
I was thinking main bearings tho or a pluged oil pick-up.
id change the oil and go up to 20-50 synt. oil and see it that helps.
good rule of thumb is 10 psi oil per 1000 rpms. but not less than 25 above 1000.

 

[jtybt]

Re: Oil pressure drops then backfire/valve tap etc

Oh, The backfire thing. Is it from the exhaust or carb. backfire at 4000 RPM can be dangerous. Do you think it's especially connected to RPM or engine temp or time running. Need it to connect it to.

Next run and backfire, stop and pull a plug just to see how hot she's running.

 

[navcon@cfl.rr.com]

Re: Oil pressure drops then backfire/valve tap etc

Engine seems to run at normal temp - 160ish.... I put my hand on the exhaust riser to see if too hot and it seemed fine, so don't think it is temp related, but I could be wrong. Oil read a little over full on dipstick when in the water, about right when on trailer.

 

[navcon@cfl.rr.com]

Re: Oil pressure drops then backfire/valve tap etc

Volvo spec 30W oil - would 20-50 be OK?

 

[Don S]

Re: Oil pressure drops then backfire/valve tap etc

Oil read a little over full on dipstick when in the water, about right when on trailer.

In the water is what counts. You don't run full speed under full load on the trailer.
Get the oil level in specs "IN THE WATER" and do another test run and see how it works.

 

[jtybt]

Re: Oil pressure drops then backfire/valve tap etc

...and engine temps have little to do with combustion chamber temps. Combustion chamber temps will most closely be revealed at time of highest running or during a problem that is happening. A minute or two of ideling could change the color of the spark plugs.


You may have a problem with a lifter or two with low oil pressure but I'm not picturing a collapsed lifter causing a backfire...unless there's a sticking valve, too.

You could very well have multiple problems.