another oil pressure thread... reasons for low #s?

[NotSoSlowSHO]

Okay, now I am getting a bit nervous. But am VERY thankful that I snagged that used pump off of ebay when I saw it. Because Im starting to think I have a worn pump. squint

I just replaced my rod bearings. And EVERY one of them look fine. No copper whatsoever exposed. Although I know that this will help my oil pressure... Id like to do what I can while the car is still down for repairs/maintenance.

So now Im looking for other reasons for low oil pressure numbers...

The obvious:

1. rod/main bearings
2. worn pump
3. oil passage restriction

So what are the not-so-obvious?

Please educate me

 

[sdpatt]

It's not #3 on your list. A passage restriction would increase the oil pressure as the pump is a positive displacement device. Ther must either be lower output from the pump or larger flow passage cross section (worn bearings).

 

[NotSoSlowSHO]

Thanks for the correction Scott... Are those the only variables then? Worn bearings and a worn pump?

Here are pics of my rod bearings:

 

[Mike Kopstain]

Kenny,

What kind of gauge do you have? I know this seems almost obnoxiously simple, but I crimped the line on my first mechanical oil pressure gauge and my readings were subsequently low.

Additionally, if you have an electric unit, you may have a bad gauge or sending unit.

With the SHO oil pumps failure rate, I would suspect a faulty gauge/ sending unit before I would suspect a pump.

Good luck sir!

 

[NotSoSlowSHO]

Although I know that they are not known to be all too accurate, I am using an electric VDO guage and sender.

At hot idle it was showing about 9 PSI.
At hot 3k it was showing 28-30 PSI.

The 9PSI I can deal with simply because of guage inacuracy. But 28-30 @ hot 3k rpm?? That seems like a BIG difference in accuracy incomparison to the idle PSI

I had planned to compare it to a mechanical guage... but now I really have a reason

Anyhow...

Id like to check the pump's clearances before I button her back up just to satisfy my curiosity.

 

[AutoSHO]

NotSoSlowSHO:
Although I know that they are not known to be all too accurate, I am using an electric VDO guage and sender.

At hot idle it was showing about 9 PSI.
At hot 3k it was showing 28-30 PSI.

The 9PSI I can deal with simply because of guage inacuracy. But 28-30 @ hot 3k rpm?? That seems like a BIG difference in accuracy incomparison to the idle PSI

I had planned to compare it to a mechanical guage... but now I really have a reason

Anyhow...

Id like to check the pump's clearances before I button her back up just to satisfy my curiosity.

I have the same gauge, I'm not impressed with its accuracy either. I wonder who makes decently accurate aftermarket gauges anymore?

 

[NotSoSlowSHO]

Autosho, which way does yours read inacurate? High or Low?

Anybody know which way electric gauges typically read? High, low? and typically by how much?

 

[Bizzy]

I've been loving my Autometer Mechanical Oil Pressure gauge. Ran it with copper tubing, and it is quite accurate as far as I can tell.

I'm gonna change the copper to AN-4 SS tubing once I find the right auction for said SS lines in a good length. From what I understand, using SS lines on a mechanical gauge shows you amazing responsiveness to the gauge.

BTW I run 42-45psi (hot) from 3300 and up to redline. and from 1500 to 3300 it is about 20-37psi. Mechanical oil pressure gauges are the *******!

 

[sdpatt]

I see little wear (much less than my 271,000 mile bearings), but a scoring line on the second and fourth bearings in the top photo. There must be some damage to the crankshaft journal to allow this score mark. Did you inspect the crankshaft?

 

[SHOZ123]

What kind of oil are you using? Is coolant going through the oil cooler? You can add a ATX cooler to the coolant line before it goes to the oil cooler to increase the oil coolers effectiveness. boink

 

[Yamaha V6]

Double check the sender - you may have the wrong sender for the gauge (even if that's the one that came with the gauge). I had one autometer that came with the wrong sender a few years ago, and the gauge was off. It's a percentage thing, for example:

on a 0-250 temp sender, 50% signal is 125 degrees on the gauge. Change the sender to a 0-200 sender on the same gauge, and 50% is now 100 degrees on the gauge.

At least, I think I got that right. I wonder if Shawn P has any insight into this. I bow to his greater knowledge, experience, & diploma.

Run down to Autozone, Pep Boys, whatever. Grab a $20 gauge set, and screw that in. If you get the same numbers, you've narrowed down the odds of it being the gauge; if you get different numbers, you've determined that it is the likely the VDO gauge. Oh, and if installed correctly, these gauges I'm referring to won't blow your tranny up.

 

[NotSoSlowSHO]

Scott:

As far as I could see and feel (which is pretty damn good) I saw no wear on the crank journals whatsoever. I looked very hard and long with a good flashlight and could not see any wear, nor could I feel any.

I do agree that there should be some kind of damage to show such marks on the bearings... but I was unable to expose any shrug

SHO123:

I only use Castsrol GTX... but the previous owner used whatever oil he found on special Very soon you will see a thread about me replacing my worn cams. Ever seen nasty cam pitting?

Fred (it is fred, right?):

I know for a fact that I bought the right sender. I remember specifically that I did. I remeber very clearly the guy at NAPA trying to sell be his "bargain" sender to go with the VDO guage. I said, "No, Ill take the VDO sender for my VDO guage thanks!"

BTW: they are both 100PSI (sender and guage)

I will have to buy another guage and sender when the time comes. I have her all torn apart at the moment... so in due time thumb