have you tried adding another qt. or so ,could it be the drain back is slow so you are running out of oil,then when you shut down it catches up...just another thought

If this is happening at low rpms mainly just idling then it sounds like the oil isn’t getting back to the pan and a quick way to find out would be jack the car up and do your warmup and as soon as it acts up shut it down and pull the drain plug and see how much oil comes out.

quote:

Originally posted by Cal of MD:

Cutting the motor off for a few minutes and starting it back up, the oil pressure would again be at 55 to 60 LBS. Once it would run for a few minutes it would drop down again to 20/25 LBS.

I say ok need to replace the oil pump, so that what we did. Guess what it did the same exact thing.
Slightly confused, any ideas?
Would it help if I put 20/50 oil in it?
O yea it never totally lost oil pressure.

Thanks for any ideas or explaintion
Cal

Did the original owner run 20/50 in it?

I'm thinking that when the 10/30 gets hot, the oil pressure goes down. When you shut it off for a few minutes the oil cools off and is thick enough to give you good oil pressure. Then after it gets the oil hot again the pressure goes back down.

Did you run it in the car it was in to begin with? Maybe you bought a turd......

The engine in my slow car "puked" sometime last year. On start-up there is a decent knocking noise that goes-away in 15 seconds or so, then sounds perfect. Shut it off, do it again, there it is..... Changed the oil, cut the filter, no metal but UGLY! Fresh oil and filter, same thing. Drop the pan, water in there already, cam and everything else is nice and milky. I am thinking crack in the block in the mains somewhere. Stock block, had a long hard life. But, if I started this and didn't let someone hear it for the first 15 seconds they would never know something was wrong with it.

You never stated that you checked the oil pressure when the engine was in the original car it came in.

There is a special length oil pump shaft for specific uses. If the distributor is not all the way down, the galley plug will not be sealed by the distributor. Or something along those lines...

This message has been edited. Last edited by: Lucas F,

Quick question for you, Cal - How much oil did you fill it with, and what was the pan's "advertised" capacity?
Asking because it may be possibly overfilled.
Here are two points from this corner for your consideration:

1. My Milodon "7 Quart" pan, holds 6 quarts in the sump. I used water to measure it during pre-assembly mock-up. Any more than that, and I get into windage issues that slow the car at least a hundredth, and cause the oil to foam badly, causing a significant drop in the oil pressure at the end of a run.
2. I once had a 1982 S-10 with a 4-banger and 5-speed. That little four could not tolerate ANY overfilling of the oil. One fourth of a quart too much, and it would do exactly what you are seeing. I also used thin oil, (10/30), and I could drive it about 2 blocks, and the oil pressure would drop drastically. Drain that extra 4 ounces off, and it was fine, would maintain pressure even in 100* heat. But the couple of times I did overfill it, as soon as the pressure drop occurred, you could shut it off, and immediately pull the dipstick, and the severe aeration of the oil was quite obvious, many tiny bubbles in that oil on the stick.

Before you spend a bunch of time & $$, check it out. Or just yank your oil filter, and put an empty full-size filter on it, (Wix 51061, Napa 1061, or equivalent). This will remove about 3/4 of a quart of oil. Then see what happens.

Steel pan? Painted? We had a car in the shop that would lose pressure, the paint had come off the pan and would get pulled up against the pickup.

any updates ?

Seen something very similar a few times before. Twice it was the oil pressure gauge (one VDO, one Auto Meter), another time it was bearings that decided to “self-clearance”, and the other time was a small crack in a main web that had ran in to the oil passage between the center main and cam(fairly common on mk5 502 blocks but have heard of similar stuff on small blocks).
Finding the source of a problem like this can be frustrating to say the least!

I had the same exact symptoms when I switched out a cam. I thought how does a new cam kill oil pressure only when it’s hot. After heating the oil in a pan on an outside barbecue to 200 degrees and pouring it in the motor, sans intake manifold, spinning it up with a primer did I see a huge internal oil leak at the lifters. The new cam with additional lift raised the lifters to the point where the oil groove was coming out of the bore. Again pressure only dropped when hot. My point is if you can remove an oil pan or an intake you can then KNOW what’s going on.

Seems to me the only thing that can happen to an engine by "shutting it down for a few minutes" is all the oil can drain back into the pan. The oil, block, crank ect isn't going to cool off enough to change anything in a "few minutes"
You said it was a Super Stock class engine so I'm going to guess the engine builder has blocked off most, or all, drain back h0les to keep the oil off the spinning crank.
Lift the intake off and see if that's case...
Or as soon as the pressure drops shut it off, put 4-5 more qts of oil in and start it up and see if the pressure is back. Obviously don't drive it around overfilled like that but at least the test will tell you if oil return is the issue....

Good luck with your problem

quote:

Originally posted by dag 1821:
any updates ?

Good morning all.
Well I blocked the relief valve where you screw on the oil filter on at, Same results. I added another quart of oil, Same result. I added another quart of oil, Same result. I changed oil pressure gauge, same result. I have not had time to try 20/50 oil yet but will work on that for sure, one night this week.
Also of note, I had the oil filter off twice now and each time it was only half full. Seems a little strange to me. But then again I'm still confused with this whole deal.
Thanks again guys.
Cal SST1177

I would check pick up for oil pump. What was previously said that the pickup might have a crack. crack opens up when hot and sucks air. shut it off and the thin metal pickup cools enough to close up crack till it warms up again.

Cal, That is rather curious, with the oil filter only being half full when removed.
Although maybe it could be a problem with aeration of the oil, as I mentioned above.
Think of the oil filter like a full glass of beer with a nice thick head on it. Once the foam dissipates, you are left with a glass that is no longer full. If the oil in the filter is full of air bubbles when you shut it off, and it sits for a few minutes, those tiny bubbles all work their way to the surface and pop, leaving the filter only part way full?
I know it seems like a stretch, but it is also one of the easier, faster, less costly things to check at this point. Drain it, put 4 quarts in, and try again...
Other than what Dave (I Make HP) suggested about drain-back holes being restricted, which would still cause the same issue no matter how much oil you add, these seem like the only 2 potential issues I can think of that would clear up after sitting for only a few minutes.

This message has been edited. Last edited by: FootbrakeJim,

Thanks again guys.
I'll be back to working on this car hopefully by the weekend. I guess ATCO is out for the SS/HA car. So now the new goal will be Cecil.
Thanks again
Cal SST 1177

Just something to think about....you can have perfect oil pressure with a pick up broke off laying in the bottom of the pan....also drain back problems would cause the pan to be sucked dry,eventually leading to "0" pressure reading....

If the pickup is indeed cracked or broken it would explain the half full filter and oiling problem caused by the oil foaming. Like sucking through a straw with a hole in it. Kind of obvious I guess but just a thought none the less.

In years of engine building I have seen 2 things that can low/loss of pressure.
Main cap oil pump boss in not flat, leaks between pump and boss. Always removed the pins and plated them flat, and some took a lot of sanding.

Oil filter adaptor not flat, leaks between block and adaptor. GM used to sell a gasket to go between, but now all the aftermarket stuff has an oring.
Oh yeah, and one other thing, the 2 bolts of the adaptor bottom out and you think it is tight but it is not.
Remember bearing clearance is nothing more than a controlled leak, so .001 or more anywhere else can affect the whole system.

The reference to having perfect pressure with a broke off pick up,was just another way of saying a cracked pick up would not be an issue.

Had an identical problem some Yeats back with a 454 I installed in my RV/Tow. Drove me nuts trying to figure it out. Long story short is was a loose oil pump. I forgot to tighten it up. Cold thick oil had pressure and as it heated up it would drop to about zip. I thought about your pickup. But if that was to close it should act in reverse.