[spectramitch]

What would cause the oil pressure to drop like this? Constant cruising speed 2400rpm. It drops slowly about 10 psi and sometimes very quickly. But it always comes back up. Running VR1 20w50 oil and the mechanical gauge is plumed at filter housing. Here is the video:
https://www.youtube.com/watch?v=Q9fI4O6kN_8

[charlie66]

Does it do in higher rpms? Mybe the pickup is coming loose? Change gage to see if the gage is the problem. Could it be loose at the back of the gage?

[spectramitch]

Accelerating it seems good. At idle it does the same thing.

[charlie66]

I would change the gage just to rule it in or out.

[spectramitch]

Once oil is hot(oil temp 180°+), pressure @ idle in neutral(1400rpm) is 20psi and in gear (1000rpm) 10psi. Is this an indicator of anything?

[charlie66]

I guess it could be but i dont see anything bad at this point. Id change the gage and go from there. See what happens .

[chuckies76ta]

Originally Posted by spectramitch

Once oil is hot(oil temp 180°+), pressure @ idle in neutral(1400rpm) is 20psi and in gear (1000rpm) 10psi. Is this an indicator of anything?

Do you still have the Pontiac oil filter housing unit installed on the block? If so I would remove it and check the bypass on it. You can always stretch the spring inside it a bit to hold the bypass close. It's held on with a tiny screw to the housing. Put a dab of blue locktite on the screw when installing. Check the disk and sometimes the metal tab is bent out allowing oil to bypass.

[PontiacJim1959]

I had a check valve in the oil pump get stuck open when a piece of junk got underneath it.

When I first fired the engine up cold, the oil pressure would rise very slow, but steady up to about 60 PSI. As the engine got warm, the oil pressure would begin to drop closer to 50PSI. The pressure would also waiver, kinda like yours. I knew I had a problem, but just did not want to pull the engine until oil pressure quit on me. So I added heavier oil - which raised pressure, but it still had issues. The pressure began to sink again, so in when some nice thick STP. Pressure went up a little again and was tolerable. Pressure was OK with RPM's and would only hit 40 PSI, but not good at idle, so up went my idle speed to 1,200 RPM ( it was a manual car) and it would hit about 12 PSI.

Finally after 7 years of this, one day I fired it up and the oil pressure was 0. My excuse to do a fresh rebuild on a 455CI I have. Pulled down the 400CI to find the a piece of trash stuck under the check ball in the oil pump so it would not close, and all the bearings were wiped out showing copper. Pics of the rod bearings are below and the mains didn't look healthy. Just a little extra clearances for high RPM racing, right?

Like suggested, change the gauge out first before assuming any big problems.

[steve25]

Pull the motor now before you ventilate the block with Broken Rods!
You have a unseated check ball issue and may have all ready caused Bearing damage.

[charlie66]

I just had a little piece of debris in my check ball. It lowered the idle pressure but never went up and down like yours..

[slowbird]

Id take about the oil filter housing, the bypass in it might be doing wierd things. It's easy to do and worth a try before going through all the trouble of pulling the engine.

[spectramitch]

Im going to swap the gauge with another mechanical. If that doesn't do the trick Ill check out the filter housing bypass. What about plugging the bypass in filter housing? The motor has a solid roller cam and driven on the street a bit and will be taken to the track. Is the sole purpose of it to open when the oil filter is totally clogged?

[PontiacJim1959]

Originally Posted by PontiacJim1959

I had a check valve in the oil pump get stuck open when a piece of junk got underneath it.

When I first fired the engine up cold, the oil pressure would rise very slow, but steady up to about 60 PSI. As the engine got warm, the oil pressure would begin to drop closer to 50PSI. The pressure would also waiver, kinda like yours. I knew I had a problem, but just did not want to pull the engine until oil pressure quit on me. So I added heavier oil - which raised pressure, but it still had issues. The pressure began to sink again, so in when some nice thick STP. Pressure went up a little again and was tolerable. Pressure was OK with RPM's and would only hit 40 PSI, but not good at idle, so up went my idle speed to 1,200 RPM ( it was a manual car) and it would hit about 12 PSI.

Finally after 7 years of this, one day I fired it up and the oil pressure was 0. My excuse to do a fresh rebuild on a 455CI I have. Pulled down the 400CI to find the a piece of trash stuck under the check ball in the oil pump so it would not close, and all the bearings were wiped out showing copper. Pics of the rod bearings are below and the mains didn't look healthy. Just a little extra clearances for high RPM racing, right?

Like suggested, change the gauge out first before assuming any big problems.

Never having a roller cam, you stated you have a solid roller. From my reading, with a solid roller the lifter bores need to have restrictors installed in the oiling-to-lifter holes or too much oil will flow, ie act like a big leak - might this be the problem? Were restrictors put in with your engine?

The roller guys can chime in as I have no hands-on experience, just what I have read in several publications.

[charlie66]

Originally Posted by spectramitch

Im going to swap the gauge with another mechanical. If that doesn't do the trick Ill check out the filter housing bypass. What about plugging the bypass in filter housing? The motor has a solid roller cam and driven on the street a bit and will be taken to the track. Is the sole purpose of it to open when the oil filter is totally clogged?

I have mine plugged . No problems. I think that you're on the right path. If the gage dont change anything then id check the bypass like suggested.

[steve25]

I had a unseated check ball once and the pressure was irratic dependant on the oil temp , but the the thing it would constantly do once the oil temp got up to 180 was the from idle the oil pressure would rise about 4 times slower when accelerating then it normally would.

[lust4speed]

You can forget about the oil filter adapter bypass causing the problem. You could totally remove the bypass flap and spring and the only thing you might see is a little increase in pressure since most of the oil would be bypassing the filter medium. The adapter bypass only determines where the oil goes inside the adapter - whether through the filter or around the filter. Now the bypass on the pump does cause problems when a chunk of crap gets lodged, but the recovery of pressure and the repeatability of the pressure drop almost seems like a lack of oil to the pump - either by low oil, pickup fell off, or possibly cavitation.

[spectramitch]

I tried a different gauge and got the same results. Could the location of my pressure gauge on the filter housing cause the bad reading? I am using a Purolator filter: http://oilfilterdata.com/index.php?v...o&model=L25288 Where is another spot to take oil pressure readings?

[chuckies76ta]

Did you check the oil filter housing ?

You can also check oil pressure on top of block by the distributor.

[chuckies76ta]

Can you post a pic of where your pulling pressure from on the oil filter housing ?

[spectramitch]

Originally Posted by chuckies76ta

Did you check the oil filter housing ?

You can also check oil pressure on top of block by the distributor.

I am going to take a look and see. Lust4speeds comment about the bypass makes sense. But I'm wondering if maybe there's something funky about the filter I'm using and the gauge line being right off of it. I am pulling from right above the oil filter on the housing.