Oil pressure question

[71sport]

I have a 71 lemans sport with 73,000 miles on it with 455 in it. Recently i put a set of gauges in it. I am a little worried about my oil pressure. When I first start it up I have about 60 lbs of pressure. After running for a while it goes down conserderably. As low as 10 lbs when idelling in gear (AT). As I give it the gas the pressure goes up, but as I let up the pressure goes down. Driving down the road its about 45 lbs. I know this is not normal, does anyone have any ideas what needs to be done or what is causing this? The car seams to run great but this worries me. Any help would be much appreciated.

[BNaylor]

What brand and weight oil are you using?

The only part I see abnormal is the 10 psi when idling if the gauge is accurate. On the 455 and 442 engines normal oil pressure should be in a range of 40-55 lbs typically at cruising speeds. The relief valve is supposed to open at 55 psi.

I've seen at idle on a warm engine around 25 to 30 lbs depending on temperature. Street cruise around 40 lbs is typical.

[71sport]

I am using 30W, Havoline High Mileage oil.

[BNaylor]

You could try multi-viscosity oil and see if there is a difference in the warm engine idle pressure. Nothing less than 10W or 15W for low side. Going back to the old memory banks low oil pressure at idle can be caused by a sticking pressure relief valve.

[MrPbody]

Yes, the relief ball may be "hung". But I doubt it...

Rule of thumb is a minimum of 10 lbs. per 1,000 RPM. The 10 lbs. at idle is a bit low. The pump "relieves" at 60 lbs. The 45 at "cruise" may indicate bearing wear, as well.

As others have said, try a heavier oil. We recommend Shell Rotella-T (15W-40).

The "fix" is to pull the engine and install new main and rod bearings, and a new pump. Watch out for the "domino principle", as the deeper you go into the engine, the more you may find it needs.

If it isn't making noise, and the oil pressure doesn't continue to deteriorate, it will probably be okay.

Jim

[BNaylor]

It could be as simple as an oil filter. I've seen pressure deviations specifically low oil pressure at idle with certain brands like Fram so it would be interesting to see what brand oil filter the OP uses.