Low engine oil pressure

[LEADFOOT]

Not to beat this topic to death, but I have read repeatedly that low pressure readings from oil pressure gauge is often a fault with the gauge itself. In my case in particular, I had the reading checked out and I was not so lucky.

When my car heats up to operating temp ~82-85 deg C the oil pressure readings on the instrument cluster are zero. Performance of the engine declines, too. I do love the car, so that's why I've come as far as I have.

I Just had new crankshaft bearings installed. I also installed a new oil pump. Almost no change from previous symptoms, only a slight improvement.

My mechanic seems to be baffled, he suggested replacing the timing chain tensioner along with 'some other things', as it might be a source of internal oil pressure loss/leakage. Okay I said, but I want a second opinion. I'm over my head here... four questions for the pro's.

1.Is this engine 'toast'?
2.Where are the areas that might be causing low oil pressure readings or internal leakage of oil?
3.What seems to be the most 'economically sound' next step?
4.What layeth on the road ahead?

I'm here to learn. Thanks...

[nglitz]

Ouch!!

I assume by checked out, you mean with a mechanical gauge right on the block?? Sometimes the senders are at fault, or so I've read.

Three basic possibilities: the pump isn't pumping, there's a blockage before the pressure sender (and therefore everything else) or there's an internal leak large enough to prevent pressure from building up.

In my experience with other engines, I've found the connecting rod beaings to be a more likely suspect for excess wear than the crank main bearings. Can we assume those were looked at and deemed Ok when the crank bearings were checked? Clean out the oil passages in the block? Filter not plugged AND the correct type? Take off the filter & crank (not run) the engine, does oil make it that far? Oil pickup connected to the pump correctly? Oil pickup screen not plugged? Pressure relief valve not stuck open? Pull off the valve cover & see if there's oil flowing up there.

A stupid silly question but so basic it's worth looking at: there's oil in the sump and the drain plug didn't fall out?

Best of luck,

[ctaylor738]

I'm no pro, and I assume your mechanic has access to the same manuals I do.

The pressure relief valve is in the oil pump, so presumably it was replaced when the new oil pump went in?

The oil flow is straight to the oil pressure sender in the filter housing via a galley - it is conceivable (barely) that the galley could be plugged or cracked and causing reduced pressure at the sender. Flow to the guage could also be blocked. Beyond that I think the only place that would drive the pressure to zero would be the main bearings. And if that was happening I would expect some noise. No oil stream to the cam lobes would confirm it.

[LEADFOOT]

Thanks for your reply, Norm
It's only a problem as the oil heats up and becomes thinner.

I assume by checked out, you mean with a mechanical gauge right on the block?? Sometimes the senders are at fault, or so I've read.

Yes, I ignored it for a while thinking it was an internal gauge/sending unit error and had my mechanic check it out with a mech gauge before he changed the crank bearings.

the pump isn't pumping,

Replaced the pump w/ OEM along with the bearings.... same symptoms.

there's a blockage before the pressure sender (and therefore everything else)

Not sure it's blockage because this only happens with hot engine (temp > 82degC)

there's an internal leak large enough to prevent pressure from building up.

I think this is it, but the leak isn't large since it seems to happen only when oil is thinned out.... oil pressure is acceptable with cold engine and more viscous oil.

....the connecting rod beaings to be a more likely suspect for excess wear than the crank main bearings. Can we assume those were looked at and deemed Ok when the crank bearings were checked?...

I do not know for a fact that these were looked at. I will verify.

Pressure relief valve not stuck open?

How would I check this? Is there a prv for the lubrication system? Duh.

there's oil in the sump and the drain plug didn't fall out?

Oil level okay.

Thanks again for relating your experience, which I lack... by the way the car runs like a champ on the open road. Just get stuck in traffic and all these symptoms become evident.

[LEADFOOT]

Thanks Ctaylor..

The pressure relief valve is in the oil pump, so presumably it was replaced when the new oil pump went in?

I will call the mech and confirm this, as a prv is not on my invoice, but is it part of the oil pump? He put in a new one. Crossing my fingers...

[MB_FanAddict]

LEADFOOT,

The oil pressure relief valve is intergraded in the oil pump according to the manual.

The minimum allowable oil pressure is 0.3 bar (4.4 psi) at idle and should be at least 3 bar (43.5 psi) at 3000 rpm (1000-1500 rpm is the norm).

I think your sensor is out of spec. If your mechanic measured 8 psi when testing the oil pressure, the gauge on the dash should have registered 0.5 bar.

What weight oil are you using?

Chris

[LEADFOOT]

What weight oil are you using?

Chris,

It is 20W-50, purposely used a heavy weight. It makes sense if the sending unit is calibrated for another range of oil pressure it will read incorrectly.
thanks,
Preston Worsham

I printed out some pages from the CD and will attempt to remove the valve cover this weekend... and check oil circulation.