[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?

[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.

[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 .

[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.

[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.

[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?

[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.

[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.

[Sirrotica]

Originally Posted by spectramitch

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.

Thing is, the by pass valve is your safety for a problem with the oil filter. Eliminating it does nothing to help the longevity of the engine. Starting the engine cold, can crush the filter media hydraulically. I can't for the life of me figure out why people plug the relief off.

If you want better filtering, a by pass filter is the way to get better filtering, not plugging the by pass valve. Pontiac is one of the engines that does not have a by pass valve internal to the filter. You have no safety valve when the by pass is plugged. The oil enters on the outside of the filter, passes through the media, and returns through the center to the internal engine parts.

Over pressuring the canister, can split the canister housing, force the O ring to leak, and crush the media. If the media ruptures, all the filtered dirt is free to pass right into the bearings. You have to ask yourself, what did I save by eliminating the by pass valve? The answer is you didn't save anything, you can ruin the whole engine if the media ruptures, and dumps all the filter contents directly into the engine. The scary thing is, you'll never know the media ruptured unless you dissect every filter by cutting it open, pulling all the pleats, and carefully examining the media. If you do find a compromised filter, the damage is already done.

If you change the filter, and toss the filter, the way you may find out is when the bearings fail, for no apparent reason. The idea for removing the by pass valve is to make every bit of oil flow through the filter. The problem with that theory is, a full flow filter filters down to 40 microns. The dirt that grinds up engine parts is small enough that it passes through the media anyway. 10 microns is the particulate size that can fit into the tight tolerances and grind away at the internal engine parts. The 40 micron size doesn't fit between the bearings and crankshaft, it can't fit in the tight spaces.

If you spend time researching, most engine builders (not every one) dismiss blocking the by pass valve as unnecessary. I've never blocked it in any engine I've ever built. If you want clean oil, a full flow filter will never provide it, the design is to filter out big pieces of dirt. If a full flow filter kept your oil clean, you wouldn't have to keep changing oil to get the small particulate out of the oil.

If you leave the oil in the engine, the small particles will keep getting denser. Everyone knows what happens if you don't change oil with a full flow filter system, sludge and engine wear ensues. Sludge is made up of the fine matter that flows through the full flow filter unimpeded.

Two ways to remove the fine stuff, flush the engine with fresh oil continually, or get a filter that removes it first pass. I use the second method to catch the fine matter first pass, rather than wait until I change oil to remove it from the engine.

One other thing, putting multiple full flow filters does decrease pressure loss across the filters, but it still doesn't remove the harmful matter that passes through a full flow filter.