Oil pressure low at idle when warm

[Andyvinn1]

98 Chevy Silverado k1500, i have a 383 stroker with Vortec heads. I installed a Howard's Cam flat tappet to roller retrofit cam, reinstalled the Melling High Volume oil pump, installed a 7 quart oil pan and pickup tube. I changed the intake to an Edelbrock pro Flo XT. Engine oil is 10W-30. At start up i get 40psi oil pressure. Mechanical gauge shows the same. Adjusted idle to 1k RPM. After warm up pressure drops to about 15psi at idle. Here is what happens.
Put in gear, RPM drops, pressure drops, light comes on. Mechanical gauge reflects the drop in pressure.
Rev engine "cable throttle" a bit, pressure goes up. Release goes back to lower pressure.
Drive it around, from 1300 rpm and above pressure reads 40 psi.
At a stop while in gear 800 RPM pressure drops down to about 5 - 10 psi. Enough for the check gauges light to come on.
Haven't really driven it due to this pressure issue, has been tuned but not adjusted the tune due to the oil pressure issue. That and it's a mechanical oil pump. Other than setting my idle over 1k RPM I don't know what it could be. Any information and things i can check would help out a lot. Also, yes the oil pressure was not like this prior to the modifications. Engine has about 12k miles on it before I did modifications. I've changed the oil to from 5w to 10w. The magnetic oil plug has some metal dust, no flakes or shavings. I have removed the oil pan to change the gasket due to it leaking. Oil pan had no flakes or shavings. I'm assuming the metal dust is from the new camshaft and lifters breaking in. No ticking or knocking, engine sounds solid.

 

[someotherguy]

Verify oil pressure using a good quality, trusted mechanical gauge. If it's still low at idle when warm then you probably have a cam bearing problem. Before panicking I would absolutely test with the mechanical gauge and be suspicious of the oil pressure sending unit.

Richard

 

[Andyvinn1]

Yes sir, I installed a mechanical gauge on the same port as the sensor. The pressure on the mechanical shows about 8 psi at it's lowest. If the cam bearing is spun what indications other than low oil pressure at idle?

 

[Schurkey]

Yup...that's lower than I'd want. The Check Gauges light should not come on at idle.

My engine pegs the 60 psi gauge at startup, using 5W-30 oil. About 12--15 psi at hot idle in gear. I'm thinking your engine has low oil pressure all the time.

Could be bearings, could be a popped-out plug in an oil gallery. Could be a bit of trash in the oil pump pressure relief valve.

What block is this? A Vortec block wouldn't need a retrofit cam and lifters.

 

[Andyvinn1]

Yup...that's lower than I'd want. The Check Gauges light should not come on at idle.

My engine pegs the 60 psi gauge at startup, using 5W-30 oil. About 12--15 psi at hot idle in gear. I'm thinking your engine has low oil pressure all the time.

Could be bearings, could be a popped-out plug in an oil gallery. Could be a bit of trash in the oil pump pressure relief valve.

What block is this? A Vortec block wouldn't need a retrofit cam and lifters.

Block is from an 84 Corvette "4 bolt main". I get above 40 psi at start up using either 5w or 10w. I have a standard pressure, high volume Melling oil pump. The block is a 383 stroker and had a flat tappet cam that was pretty mild. If the cam bearing was bad would i have low oil pressure at any RPM? I don't have any knocking or ticking. Engine runs and sounds good, other than the oil pressure being low when the oil is hot. I put a lot of money into the motor don't want to break it this early in it's life.

 

[Schurkey]

I get above 40 psi at start up using either 5w or 10w. I have a standard pressure, high volume Melling oil pump.

Seems low to me. I'd expect 60+ psi. But maybe San Antonio heat is more than I'm used to.

If the cam bearing was bad would i have low oil pressure at any RPM?

Sure. But there can be other causes.

 

[Frank Enstein]

An oil cooler can help. Using 10w40 oil should give you higher pressure when hot. Synthetic oil can keep your hot oil pressure higher because it is more thermally stable. Bearing clearance on the high side bleeds pressure as will loose clearances in the pump. I generally recommend .002" for rods and mains under 500 HP on a sbc. Maybe .0025 on the rear main.

 

[Schurkey]

An oil cooler can help.

I'd want to document that the oil is getting overheated before I went to the expense of an oil cooler; and added a bunch of potential leak-points to the oil system.

My impression is that this is a mechanical problem, not a thermal problem...but I've been wrong before.

 

[L31MaxExpress]

I'd want to document that the oil is getting overheated before I went to the expense of an oil cooler; and added a bunch of potential leak-points to the oil system.

My impression is that this is a mechanical problem, not a thermal problem...but I've been wrong before.

My oil pressure came up 10-15 psi at idle after installing the factory in-radiator oil cooler on my 97 Express van. Texas heat is brutal.

 

[Frank Enstein]

I agree. Just trying to help him keep the oil pan on for now.