I'm a little stumped. 1999 LS 4WD. When the engine is up to operating temps, I noticed that the engine oil pressure will increase by approximately 100 kPa (about 10 PSI) when I lift my foot off the accelerator. At idle, the oil pressure will sit steady at 125 kPa (about 15 PSI).

I did search and found some references to the PCV. I removed it and it checked out ok. Boots for the PCV are old, but snug. I replaced several smaller vacuum lines that looked heat checked.

Any ideas?
Tim

 

Not too sure what you are asking??? Is oil pressure dropping as RPM increases? Should be the other way around. 15 psi at idle is fine. As for manifold vacuum, you will see a drop as the TB is opened, and increased vacuum at idle.

What issues (besides gauge fluctuation) are you having? Any codes present?

EDIT: Pressure dropping on RPM increase could be low oil level or loose/broken/plugged pickup tube causing starvation........

How is the pressure on first startup of the day? Is it good, and then drops slowly across the board?? Could be a sign of worn bearings or pump failure.


Aaron

 

Sorry if I was a little unclear. Start-up and run oil pressure is ok, 125 kPs at idle (15 to 20 psi) and 200 kPa at 80 kmp (50 mph) at operating temp.

As an example, at 80 kmh (50 mph), oil pressure is at 200 kPs (30 psi). If I lift my foot from the gas pedal, the oil pressure immediately increases to 275 kPs (40 psi). This increase in oil pressure seems to increase directly in proportion to an increase in intake manifold vacuum.

No codes, engine performs fine. No other issues.

I read that a faulty PCV could have an impact on oil pressure, but as I said before, the PCV seems fine.

Tim

 

Are you sure you dont hear piston slap {knocking} at startup? Sounds like bad bearings to me.

Did it possibly have coolant in the oil? Suggestion: Run 20w 50 Synthetic and call it fixed.

 

Perhaps I'm misunderstood. I don't have a low oil pressure problem, rather a variation in oil pressure I'm trying to track down. No coolant in the oil and no oil in the coolant. No loss of coolant. I know the difference between piston slap and bearing knock. I have neither. Oil consumption is nearly nil. I use 20w 50 in my air cooled 911, but 10w 30 in both my BMW and Blazer.

So, anyway, what would happen if there was a lower intake manifold leak between the air/fuel intake and the oil gallery that did not include the coolant? Could a variation in vacuum in the crankcase caused by a LIM leak vary the displayed oil pressure?

 

I believe in theory yes...but idle quality would be dramatically poor. 02 readings and fuel trims would be jacked. You have not indicated any of those concerns.
Perhaps your oil pressure switch or gauge is the issue?
A mechanical oil pressure test would be a good next step.

 

Did you check the OTHER side of the PCV system.. from behind filter to engine?
To check for intern vac leak pull both pcv lines, plug one hole check other one for strong vac

You're right, if no noise at startup probably not bearing related.

Yet that is a symptom of worn main bearings IIRC

Actually the numbers you cite for oil pressure are low, at least compared to mine. Engine idle at just warmed up is over forty and I'm pretty sure I'm not running a thickener.

 

I would install a mechanical guage. (Temporarily) That way you know if the pressure is actually doing what it looks like its doing. Hate to suspect the motor when its actually the electronics!