Low oil pressure after long high speed run

[dammstrate]

I have a 502 stroker in my 64 Belvedere. Makes almost 500hp at 6400rpm at the wheels, 11.0:1 comp. Idles at 50-60psi, and stays there for most easy driving.
I haven't had the car that long, and took it out and ran it hard for about 25-30 minutes at 70-80 mph, about 4000 rpm. Ran like a top and oil pressure stayed at that 50-60 psi level. Temp was steady at about 190 degrees. Got off the highway and slowed to a stop at the light, and oil pressure dropped to 15-20psi. Would jump up to 50 if I revved it, but than went back down to 15-20. Scared me a bit (WTF?) and I drove slowly (40-45mph) home, stopping a every 5-10 min.
Pressure gradually rose back up at each stop, I guess as the oil temp cooled off. What could cause this? Clearances? Non-optimal oil type/viscosity? Guess I should know the oil, but I don't know what was in it when I bought it.

Any comments?

 

[threewood]

15-20 psi is plenty. Mine starts cold around 75psi and when hot drops to 12-15psi at idle. Jumps right back up on throttle.

 

[BSB67]

I think it’s fine.

 

[Dave6T4]

Try running 15W40 Rotella. I don't like synthetic for older engines.

 

[Geoff 2]

I run 10w/60 in my engine. Best of both worlds. [1] it is non-friction modified & [2] Full syn.

 

[Wietse]

Quite clear it is temperature related.
Since you do not know what oil currently is in there makes it a little hard to get a reference for what oil to select if you want to increase viscosity.
If there was a 10W40 in there you could go up to 20W50, this will be a bit thicker at higher temperatures and give a little more pressure.
Your current oil pressure is not that bad, and the fact it instantly increases when revving up shows the lubrication system is able to build up pressure and there are no major leak-offs like a worn/damaged bearing or other types of pressure loss.
I am using the Valvoline VR1 20W50, with a high volume oil pump and have 50-60 psi (hot) all day, if i drive it hard for some time it would go down to 40 psi but lower than that i have never seen it. (i got 2 pressure gauges, 1 in the dash and an additional one)

 

[DanielSlocum]

If you had 50-60 psi at idle.....sounds like your pressure relieve valve in the oil pump was stuck. Now its unstuck and your idle pressure is normal for that high rpm engine.

 

[gkent]

I'd be overjoyed if I had 15-20 with hot oil at idle !!

 

[dvw]

My bet is this is purely a function of oil temperature. Going to thicker oil willl raise the pressure. But is it necesary? No, oil cools as well as lubricates. Thinner oil flows quicker carrying away heat from internal components. Being a hot rod engine, clearances are looser. Low idle pressure just means the the pump can't overcome the rate of flow when warm. 15-20 idle is plenty. What matters is that it increases with speed. I'd like to see 60 psi hot at high rpm. It it's close to that you are fine. You didn't mention what pump or capacity pan. More capacity and/or pump volume will help.
Doug

 

[Runcharger]

I think 50-60 at idle is higher than necessary. 15-20 after sustained speed in the heat is fine. I don't think I would change anything. If you do anything I would increase oil pan capacity or add capacity with an oil cooler and related lines. But an oil cooler adds a bit of restriction.

 

[ckessel]

I gently put a fresh bullet in my 67 wagon, 440, with the standard volume/pressure pump. It currently has 30w Amsoil break in oil. This is what I have hot at idle and going down the road at 60. When I go to the 10w-30, it's going to drop. Therefore I have a M63HV pump coming and will install that when I do the oil change to the 10w-30.

 

[Rebelrouser]

I have a 502 stroker in my 64 Belvedere. Makes almost 500hp at 6400rpm at the wheels, 11.0:1 comp. Idles at 50-60psi, and stays there for most easy driving.
I haven't had the car that long, and took it out and ran it hard for about 25-30 minutes at 70-80 mph, about 4000 rpm. Ran like a top and oil pressure stayed at that 50-60 psi level. Temp was steady at about 190 degrees. Got off the highway and slowed to a stop at the light, and oil pressure dropped to 15-20psi. Would jump up to 50 if I revved it, but than went back down to 15-20. Scared me a bit (WTF?) and I drove slowly (40-45mph) home, stopping a every 5-10 min.
Pressure gradually rose back up at each stop, I guess as the oil temp cooled off. What could cause this? Clearances? Non-optimal oil type/viscosity? Guess I should know the oil, but I don't know what was in it when I bought it.

Any comments?

Two ways to build performance engines, old school loose bearing clearances and thick oil, modern way, thin oil, tight bearing clearances, your engine was built the old way looks to me. The old way has some advantages for a stock block, loose clearances allow some flexing of the block and crank so the crank does not grab a bearing and make it spin under heavy loads. as long as the oil pressure picks up when you touch the gas you have no issues. If you read the service manual most oil pressure specs are at a certain RPM not at idle. OEM light comes on about 7 psi for that very reason.

 

[j-c-c-62]

My bet is this is purely a function of oil temperature. Going to thicker oil willl raise the pressure. But is it necesary? No, oil cools as well as lubricates. Thinner oil flows quicker carrying away heat from internal components. Being a hot rod engine, clearances are looser. Low idle pressure just means the the pump can't overcome the rate of flow when warm. 15-20 idle is plenty. What matters is that it increases with speed. I'd like to see 60 psi hot at high rpm. It it's close to that you are fine. You didn't mention what pump or capacity pan. More capacity and/or pump volume will help.
Doug

I am in agreement with this thinking.
Even though it by consensus here may be fine currently, which I also agree with, it is IMO an indicator the oil is definitely getting hot, and you are maybe close to the edge in that regard. Meaning on a very hot day, big head wind, steep incline, car fully loaded, or 1/2 qt low, etc you might cross that edge of "fine" with overly hot oil. If other suggestions above don't give any significant pressure improvements at hot idle, any external oil cooler would gain the OP a bit of operating temperature margin at idle and speed.

 

[Cranky]

Also wouldn't hurt to install an oil temp gauge.....

 

[Fran B]

If you want piece of mind get another filter. Add some oil to it remove old filter, put on new filter. Add oil that you djdn't put in filter and start engine to fill filter. If you don't start you may lose prime by oil draining out of pump. Now cut the old filter and inspect for metal flakes. Good luck!

 

[j-c-c-62]

I can't think of any situation in a high-performance engine metal (meal?) flakes in the oil is not an indication of an already in progress catastrophic engine failure.

 

[dvw]

We've run filled blocks on the street by adding an oil cooler. Worked fine.
Doug

 

[MWbirdLOVER70]

My old school way of thinking 10lbs per 1000 rpm. My idle warm 10-20lbs

 

[1967coronet]

Running under load at 4,000 rpm for a 1/2 hr..that is a pretty good test run lol.
Im like the others thinking mabey a little thicker oil.
I never seen posted what your running in it for oil.
For loading the engine for 30 minutes at 190 I think it did pretty well.

 

[dvw]

Mine is loose. Except the lifter bores which are bushed snug. It will easily go over 100psi with 30w. It gets run with 5w25. .0027" rods, .0034" mains. Bearing clearance doesnt affect pressure anywhere near what leaky lifter bores will. Think about the size of the oil hole in the lifter bore. Its huge.
Doug