[chiphead]

I was visited by the low oil pressure goblin yesterday on a cruise across town. Engine is a 69 400 with 62 heads, unknown history or mileage. Does seem to have a lot of miles on it. There's bearing material in the head's oil returns that has been there a long time. Lucas 10w30 hotrod oil.

During a cruise, oil pressure was 45 PSI at 2200 RPM, water temp was 185F, which is normal for this engine. I did a 4500RPM 1-2 shift and 4700 RPM 2-3 shift from a stop. After 2 miles I came to a light. My idle oil pressure dropped to 10PSI at 900 RPM, where it should be 20-23PSI. Oil pressure was sluggish to respond after that, didnt want to get over 35 PSI at 2200 RPM. I got home, gave it a few revs and the oil pressure came back. After it cooled off the oil pressure was about where it should be. I'm sure there's valve seal debris in the oil pan, I found all the valve stem seals mashed in this motor when I did the cam. Cam bearings had some life left in them. Lifter valley was really clean when I did the cam.

How do I tell the difference between a stuck relief ball and a motor that's really hurt?

[steve25]

A motor that has low oil pressure due to hurt bearings does not ever go back to having normal oil pressure again, so that's not a option here.

I guess is that you either had a very small sliver of that chewed up valve seal material holding the oil pump bypass open some for that driving time or maybe your oil filter is having problems.

This assuming you have a mechanical pressure gauge with no sender to screw up.

[i82much]

I have seen noticeable oil pressure drops after wacking on my car a little .... it gets better after cooling off and a restart.

[leeklm]

Pretty common to have 10psi at idle once the oil is good and hot. Mine was refreshed recently and has tight bearing clearance and lifter bore restrictors. 10/40 Oil pressure is similar to yours until a couple of drag runs, then about 12psi at idle until things cool down a little.

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[mgarblik]

If I have my fresh engine fully warmed up and go out and run the hell out of it, (which I will do), my oil pressure will be 10-15 PSI at 900-1000 RPM. That is 10W-30 VR1 oil. When I then drive it, the pressure will immediately jump up however to around 40 PSI @ 2000 RPM. If your really concerned, send an oil sample out to Blackstone Labs. The guessing stops there. Not very expensive. Also listen for new/different engine noises as you slowly rev the engine from idle to 3-4K RPM/s.

[Vid]

If there is debris floating around in the oil, could possibly be the oil pressure sending unit. That little pin hole can clog easily especially after a fun little romp. Glad it came back to normal.


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[chiphead]

It's a mechanical autometer gauge mounted under the dash. Plumbed to oil filter housing. It's usually 50 PSI at cold start and drops to 20-23 PSI at 850 RPM hot. I plan on cutting the oil filter apart and see what's in there. I'm surprised so many of you report the loss of pressure after a hard run. I had not seen that with this motor yet. Of course I haven't really been running it hard, I've just gotten the car sorted out. The engine is strong, the stall converter and 3.25s is fun. With 275DR and trutrac, it grabs and goes. Only thing I don't like is the quarterstick shifter.

The engine has about 200 miles and two oil changes on the new cam. Should the oil filter be clean or is small metal OK in the filter?

[Dragncar]

The only time I have ever had one of my engines with 10lbs of oil pressure I freaked out and pushed it on the trailer and in the garage and pulled the engine. This was years ago and I just changed the oil pump to my old pump I blueprinted myself.
Oil pressure came right back to 75lbs cold, 60 hot down the track and 45 lbs at a fast idle. 1200-1400 RPM.
The pump could have a piece of debris in the check ball.
Never had a engine that was 10-20 lbs hot. But I have always ran 20-50 or 15-40.

[Gach]

10w30 Is very thin oil, and could be possibly causing what your experiencing I would go to at least 20-40 oil, preferably Valvoline VR..1 Drain oil and look at it good. Then put some 20-40 Valvoline in there. Change oil filter cut it open just to check.

I experienced same situation on a 67…400 ci motor I did for a friend. Come to find out he was using 10-30 W. Made the change and oil pressure was perfectly normal after that. Definitely can’t hurt to try this.

[chiphead]

Closing the loop on this.

I changed the oil to 10W40 and cut the filter apart. I found a small piece of blue masking tape stuck in the filter pleats. I used the tape to block off the top end while I did the cam change. I'm guessing a small piece fell into the pan, the oil pump ate it and it got stuck in the relief. Eventually the pump spit it into the filter, which trapped it. Since then, the oil pressure has been 20-22 PSI hot idle and climbs with RPM like it should.

[PunchT37]

Originally Posted by chiphead

Closing the loop on this.

I changed the oil to 10W40 and cut the filter apart. I found a small piece of blue masking tape stuck in the filter pleats. I used the tape to block off the top end while I did the cam change. I'm guessing a small piece fell into the pan, the oil pump ate it and it got stuck in the relief. Eventually the pump spit it into the filter, which trapped it. Since then, the oil pressure has been 20-22 PSI hot idle and climbs with RPM like it should.

LOL.


Time for a trip to Vegas?

[will slow gto]

Dang! If only they could all have a happy ending. ��

[steve25]

Blue painters tape is .004” thick and this just goes to show how well - once your oil gets hot enough a check ball gap of that amount can bleed off pressure.

[tjs72lemans]

I'm surprised that could make it's way through the oil pump pickup screen.

[Formulajones]

I'm surprised at all the people that say when they beat on their engine their pressure drops too, as if it's normal.

I've never had any engine do that.

[64speed]

If I let my engine warm totally up I and drive it I have great oil pressure. Goes up and down with engine load and rpm like it’s supposed to. If I free rev it in the driveway with no load it will drop from 35 hot idle to about 30. Weird but who knows.

[steve25]

That may be because in a free rev/ no load condition the motor is not making the added crankcase pressure ( Minor blowby ) to push the oil into the pump.

That’s the only thing I can think of for such a thing to take place while the car is stationary.

Formulajones, the only time I have seen that happen was during crazy driving maneuvers , so I too question the condition of people’s motors that say that .

[Formulajones]

Originally Posted by steve25

Formulajones, the only time I have seen that happen was during crazy driving maneuvers , so I too question the condition of people’s motors that say that .

yup

[JB Eng Wis]

I would change the oil. And I would go thicker.... i would even go as high as 20w-50
Just try it..... if ists to much then find an inbetween weight,,,, Pontiacs are tuff engines.

[grandam1979]

3 bolts to take the filter housing off check bypass and reinstall 1 hour tops with basic tools. Hardest part will be cleaning up old gasket.