[jww]

OK, this is a new motor with maybe 150 miles at most. It has a high pressure pump from Kauffman, but it's just a stock pump....nothing blue printed/exotic.

Driving, the pump carries 60-65# but then it will drop to about 40# and stays there. When the rpm's drop a little it will jump back up to 60#, but then soon drops off again. I was watching it in the driveway this morning and it does the same thing. Oil pressure was about 60# on fast idle then I noticed it was down to about 40#. Increasing the rpm up to 60-65# it suddenly drops off to 40#.

My guess the bypass is opening, but thought I would poll the experts for their take on this issue. I took pump apart to look for any foreign material when I put motor together, but made no mods to it myself.

Gauge is a new S&W mechanical and picking up the pressure off the oil filter adapter.
10W-30 with a Wix filter. This is the second oil change as I have removed the break in oil and filter. 1st oil filter did have some debris in it but very experienced engine builder friend of mine said it looked normal to him given it was a new motor.

No other problems with this engine that I know of except for the noisy H/R Comp Cam lifters! That's a whole 'nother matter!!

All rods were between .0015 and .002 when I put it together (using plastigage)
Mains .002
Thrust .008

Thanks in advance for your comments.

Jerry

[somdgto]

I would agree that the bypass is creating the variation. When you had it apart did you make sure the spring was seated correctly and the correct length? Also would advise changing the point where you are picking up your pressure. The port in the back of the block next to the distributor will give you a much more accurate reading of the pressure actually in your engine.

[jww]

somdgto:

Regarding your question about the spring.....I put this motor together back in July, but pulling the spring and plunger out and replacing is a pretty simple matter. I suppose I got it correct, but I've done dumber things before! LOL

Yeah, I read numerous posts about picking up oil pressure there by the dist. I'll change that around, but might be a few days before I get to that.

Appreciate your suggestions greatly.

Jerry

[Rick Jones]

From what I read, an engine requires 10# of oil pressure for every 1,000 rpm, so a traditional Pontiac 60 psi oil pump is good up to 6,000 rpm. You can change pressure by changing grades of oil (5W20 will be lower pressure than 15W40). More pressure is not always better and can be a sign the oil is too thick and not flowing through the engine quick enough to adequately cool and lubricate.

Here is some interesting info on oil:

http://www.bobistheoilguy.com/motor-oil-101/

Thanks, Rick

[lust4speed]

If there is something stuck in the bypass, your oil pressure would continuously stay at 40 and not bounce between 65 to 40. If the pressure goes up and down, it's probably not the bypass causing problems.

I'd probably start with substituting out another pressure gauge before tearing into the engine.

[jww]

Hi, Mick.........you know that very same thought occurred to me in the shower last nite!!

If something was holding the check ball off the seat it couldn't reseat itself again.....duh!!
Glad you confirmed what was going thru my mind, as well.

Have a new S&W mechanical gauge but I'm leaning toward that or my picking up the pressure at the wrong point.

BTW.......for those interested my Stewart Warner gauges are stamped "Made In Mexico"
Here's hoping it's the gauge!

thks, Jerry

[68GoatMan]

Man, just went through something similar, except my oil pressure was only 7lbs @ idle. After going back through motor and replacing all the Bearing's, I also went one size smaller on the check valve. My ball was stuck. Hope you get it figured out... On the bright side, at least you have decent pressure.

[68GoatMan]

Oh and my engine builder forgot the gasket on the oil pump. Something to check for....

[jww]

Thanks, Goatman:

I recall reading some of your exploits regarding your lost oil pressure. When you say your checkball was stuck I assume you mean stuck open?

My pump might be OK because as I stated my oil pressure is good then drops by 20# or so. I'm hoping it's the gauge or where I tee'd into the oil filter adapter...guess that's not good thing to do. I'm gonna work on this today and see what I come up with.

Thanks for your comments.

Jerry

[jonmachota78]

Is your filter bypass blocked? What kind of filter? Electric guages?

[jww]

Update:

Moved mechanical oil pressure line from the oil filter housing to the port located at the back of the block just under the distributor body. (quite a job, btw). This made no difference in the fluctuating oil pressure. Replaced the gauge with another and still doing the same. So I can't think of anything else besides the oil pump check ball ????

This is high pressure Melling pump. What kind of pressure should this put out at say 2K RPM? Back in July when I first started this thing IIRC it approached 75-80# when cold and now about 60-65#.

Would it be possible that there is something really small under the ball that lets it leak by a little until it reaches 60# then the pressure opens the ball more making it drop to 40#?

Regardless looks like I'm gonna have to pull this thing. This is a 4.5 year restoration and I sure hate to start skinning up my paint because of this!!! Frustrating, but it happens to all of us.

Anything I may be missing??

JWW

[ponjohn]

What brand filter?

[jww]

Current manufacture AC-PF24. I misstated in the opening text that I had a WIX filter on it, but was mistaken. When I first fired the motor I'm positive I had a WIX on it, but after the first oil change I must have installed the AC that's on it now.

Think I'll put a new WIX or NAPA Gold on just to see if it makes any difference. Anybody have any oil filter stories that might explain this pressure drop?

Thanks, Ponjon.

JWW

[Cliff R]

Pressure drop on a hot engine is most often caused by excessive clearance(s) someplace.

All Pontiac engines I've built here have shown 60 psi fully warmed up past 2000rpm's. Most idle around 20-30psi, varying mostly due to how hot the engine and lube oil is. Engines that we've worked on that had less pressure than that, had internal "issues" someplace.

I have ran into filter issues with several brands/types of filters for these engines. NEVER once had any success with the smaller filters on them. Oil filters can fail and cause pressure related issues, so at least start there before tearing into it.

The oil filter will also tell you what's going on inside the engine. If it's full of metal and other debris, the engine needs to come out for inspection, BEFORE it grinds something up pumps enough junk thru it to ruin the entire assembly......IMHO.....Cliff

[jww]

Thks, Cliff..........

Yeah, I'm going to try another filter before I pull this thing out.
This car carries 60-65# (hot) until it gets to 2000 rpm or so then suddenly drops off to 40#.

I can rev it up again and it climbs back up to 60# then drops again and so on and so on.
Wouldn't think bearing clearances would act that way.

Do you know the part numbers of your filters?

Thanks, Jerry

[jonmachota78]

maybe try adding another quart of oil and see if i behaves the same way.
but conversely:
Buddy of mine has a 502 chebby, and it was loosing oil pressure when the rpms went up. it now keeps good pressure at high rpm with a quart LESS oil!! go figure. All we could figure was more oil caused more whipping and bad oil control.

[Cliff R]

My current engine will do something similar if it gets low on oil. I'm using a Morroso 7 qt pan, and it doesn't like less oil than that in the system or oil pressure will fall off, then go back up slowing increasing rpm's up past 2000 or so.....Cliff