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  #1  
Old 09-30-2004, 09:35 AM
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Low engine oil pressure

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...

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  #2  
Old 09-30-2004, 09:58 AM
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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,
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  #3  
Old 09-30-2004, 10:51 AM
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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.
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  #4  
Old 09-30-2004, 11:16 AM
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Oil pressure good when cold engine...

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

Quote:
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.
Quote:
the pump isn't pumping,
Replaced the pump w/ OEM along with the bearings.... same symptoms.
Quote:
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)
Quote:
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.
Quote:
....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.
Quote:
Pressure relief valve not stuck open?
How would I check this? Is there a prv for the lubrication system? Duh.
Quote:
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.
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  #5  
Old 09-30-2004, 11:20 AM
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Oil Pressure Relief Valve

Thanks Ctaylor..
Quote:
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...
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  #6  
Old 09-30-2004, 04:48 PM
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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
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Last edited by MB_FanAddict; 09-30-2004 at 05:03 PM.
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  #7  
Old 09-30-2004, 05:37 PM
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20w-50

Quote:
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.
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  #8  
Old 09-30-2004, 05:49 PM
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by the way the car runs like a champ on the open road.
________________________________________________________________
I don't know if this will make you feel any better...but many years ago when I was in high school I had a '41 Ford with the V-8 flathead engine that had an absolutley zero oil pressure reading after the engine warmed up. I drove that car thousands of miles and th engine never missed a beat. I am sure the low pressure was because the main bearings and the rest of the engine were very high mileage and worn...but as I said, the engine ran fine and was still going strong when I sold the car a couple of years later.
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  #9  
Old 09-30-2004, 07:06 PM
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Put a new sender on it. Cured my problem.
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  #10  
Old 09-30-2004, 10:59 PM
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M103 engine

Quote:
check the rail and see if it is damaged, please let me know what you find
I will print this page out and take it to my mechanic, tomorrow morning. This sounds like it could be the problem. Thanks, Ray, and everyone else for feedback... just can't beat the benefit of experience from others who have been there. I'll post the results. After almost 1400 bucks and 3 weeks with no car, I'd like to stop paying to troubleshoot and get this fixed so I can move on to those Euro headlights!!

Thanks again to all and God bless. This forum is the best!!!!

Preston Worsham
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  #11  
Old 10-06-2004, 11:51 PM
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Out of curiousity, did your latest attempt fix the low pressure 'hot oil' problem?
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  #12  
Old 10-07-2004, 06:04 AM
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Quote:
check the rail and see if it is damaged, please let me know what you find
This is still on the list...Have to take it to the mechanic next week.

Meanwhile, I verified that oil is circulating to the top end after driving on the hiway for a while. I also know that the sending unit is working correctly.

I'll let you know what I find out. Thanks....
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  #13  
Old 11-11-2004, 10:37 AM
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Exclamation Update to previous post...

The car has a new timing chain, guide rail, and tensioner. The symptoms are the same with respect to oil pressure when hot. So, new bearings rear and front seals, oil pump.... and a couple thousand dollars did not "fix" the symptom on the dashboard gauge.

I think it runs much better than before but the oil pressure still goes to zero at low rpm like once it gets hot like in heavy traffic, then it's like an old diesel with respect to the of sound of knocking and lower HP. Could it be something simple like the oil filler cap? Maybe the valve guides need replacement? What should I try next?

Any expert opinions what would it be better to let it go or keep trying to fix this?

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  #14  
Old 11-12-2004, 01:58 PM
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Quote:
Originally Posted by LEADFOOT
the of sound of knocking
Evil. The oil is going somewhere, and it's not to the bearings.
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  #15  
Old 11-12-2004, 03:52 PM
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Quote:
Originally Posted by LEADFOOT
...then it's like an old diesel with respect to the of sound of knocking and lower HP.
That is NOT GOOD. Your bottom end is not getting oil, and your engine is on borrowed time, and it's running out FAST. You're either going to have to solve this right now or you're looking at a new engine.

Somewhere, something is not right. Forget the sending unit, if it was faulty, pressure would be good and you'd not hear that knocking. There is indeed no pressure. With new bottom end bearings and a new oil pump, you might want to be in the face of your mechanic and ask why there is no oil pressure. Pick up installed wrong? Pump faulty?

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