Hi guy's
Lately I've noticed something thats concerning me. When I do a full throttle pull, at approximately 5000RPM I'm losing a lot of oil pressure. It's a 455 .030 over with 3 or 4 thousand miles on it. Runs great and pulls like a freight train. It idles at 20 LBS hot and runs from 50 to 70 LBS when driving normally depending on throttle position. I see it dropping quickly to 40 or less when it really starts to rev. I didn't have an oil pressure gauge on it until recently. I've done many of these pulls, and it's fine, but I'm concerned about longevity. Today I did a test where I dropped it into second gear at 60 MPH (TH350) to see if it was an RPM thing or a g-force thing. It's definitely a RPM thing. So what might cause it to lose oil pressure at high RPM? It's a cheep stock replacement oil pan and pick-up. I think I put a high pressure oil pump on it, but not a high volume pump. Due to the rumors of Olds pumping all the oil to the top and not draining back down well. Maybe this was my mistake? I run a 10W40 oil made for these hyd flat tappet cams. Lots O Zink and such.

Thoughts?

 

Put some electrician's tape over your new oil pressure gauge and keep driving.

 

Try changing the filter before you dive into all the conspiracy theories. 😉

 

40 PSI is still plenty of OP but you also state "or less". How much exactly is "or less"?

 

Cut the oil filter open. If you have done any damage, you will find the debris in the filter.

As crazy as I sounds, you may have too much oil in the engine. If the crank is sitting in the oil, at high RPM the oil can get churned up into a foamy mess. AIr in the oil inst compressible, that could account for the lower high rpm oil pressure. Try taking a 1/2 quart at a time, while watching the oil pressure CLOSELY.

Does it have a aftermarket pan? Wrong dipstick/tube?

 

It is an aftermarket pan. I think it was advertised as a 5 qt pan. I would assume that means I should run 5 quarts plus what ever fits in the filter. But I've heard they often exagerate the capacity of these pans. This summer I started with just 5 quarts after I saw an episode of engine masters where they dug into oil levels and windage. After I saw the drop in pressure I added 1/2 a quart. It didn't get better. I don't think I want to go less that 5 quarts. I might try 6. As far as the dip stick and tube...they are the wrong ones. But I'm measuring the oil going in and checking the dip stick for what it looks like "full". Anyone got a stock tube and stick for a 455 they wanna part with?

 

The factory dipsticks and tubes are getting harder and harder to find.I have an aftermarket 5 qt.pan and the cheap dipstick and tube on my 455 . When i initially filled it with 5 quarts of oil i made a small file mark where the oil level was on it. the line is well above the factory mark on the dipstick but i now have a benchmark to go by .As far as the drop in oil pressure i cant comment on but ,Matt may be onto something

 

Did you run the engine to fill the oil filter and then allow time for the oil to drain back from the heads before you checked the new dipstick? If not, your scribe mark is too high.

 

Yes, ran the engine to get the oil flowing then shut it off and let things settle.

 

It’s common practice with high capacity oil pans to run the engine with less oil thsn the pan holds you want the crank out of the oil. If the crank is in the oil, it will get foamy. Air can be compressed, a liquid can’t. That means any air will lose pressure, and not lubricate the engine.

the factory pan holds 4 quarts. Adding 4 quarts to a 5 quart pan is basically stock, but with the oil level lose in the pan, away from the crank.

 

Any updates to the oil pressure drop?

A friend of mine is experiencing the same thing. Olds 455 has good oil pressure but when doing a WOT run, pressure drops from 50 psi to 20 psi, so he then gets off of it. It has the 7 quart Milodon pan but I wonder if those pans are truly 7 quarts or more like 6 quarts plus the filter?

 

I have a 7 quart aftermarket pan, with a factory dipstick and tube. I run my oil level at the “ADD” point on the dipstick. It takes about 7 quarts to do an oil change. Oil pressure stays around 55psi at full throttle, and has been together for almost 18 years.

If you have any question if the engine has been hurt, cut open the oil filter. Any shrapnel will be caught in the filter media.

 

I have largly followed "Bangscreech"s advice and ignored the gauge and kept doing what I do. My pressure is in the 60 to 70 range and drops to around 40 during wot pulls at around 6000 rpm. I have a cheep oil pan that claims to be a 5 quart pan. $65 at summit if I remember it correctly. I don't remember if it even had a baffel in it. I've experimented with running it a quart low with no measurable differance. I assume its a windage issue. Aerating the oil when it gets wound up that high. Maybe I'll cut the oil filter open this spring when I do an oil change. I have never done that. Might be interesting.

 

Windage is a good chunk of the problem. Aeration of the oil is only part of the problem, the bigger problem is oil returning to the pan. No it's not because it's getting stuck in the heads but the return from the heads is poor. A lot of guys get stuck thinking that what works at the drag strip or dyno will work on the street or water, it doesn't always work that way. Going down the highway at an elevated RPM will pull oil out of the sump. This will lower the available quantity of oil at the pump. Now you stab it and the oil level decreases even more. The oil that was once in the sump is now all aver the place and has to drip down to the sump. On the way there the crank will wip it up sending it any wich way and adding more air to the oil emulsifying it making it worse. At the drag strip it's easy just use a large pan to have reserve to make the run without worrying about drain back. In the water and the street this may not solve the issue. Due to extended high RPM the issue just amplifies. This is where oil control come into play. Biggest help is a good windage tray with some oil stripping device. The cheapest rout is to add more capacity.

 

A baffle in the oil pan sump is important too. On acceleration, the oil forced to the back of the pan/sump.

 

Assuming it has a bypass or oil pressure control valve, maybe it's relieving at the high pressure you see to maintain the 40 psi. Filter could be relieving also, relief valve in them are iffy.

 

"Duh" recommended changing the oil filter before panicing. I haven't done that yet. I will when the snows gone and spring is here. Maybe thats all it is. I doubt it...but maybe.

 

Good place to start. That way, you can cut into the filter and see what you can see, and if there's nothing to worry about there, replace it with another that may not have a sticky bypass valve (as noted above).

 

As stated above if you find nothing in the filter and your oil pressure numbers stay consistent you really don't have an issue. If your normal oil pressure declines over time you have an issue. While a loss of oil pressure like you have is not ideal it is not uncommon.

Oil pressure is an indicator that:
1. You have flow.
2. How fast your system is leaking down.

Don't worry about the absolute number.

FYI. When cutting the filter open use the correct tool. Using something else can cause "stuff" to get in

 

Tin snips work great. Or clamp the filter in a vise, drive a screwdriver thru it, and twist it open. Definitely don’t use a saw, it’s hard to tell cutting debris from saw debris.