Oil pressure

[datsun280z]

Hello,

After a 30 minute drive the oil pressure in my Ford 302 Engine
drops slowly from 50 to 20 ( well.. that's what i see on the gauge ).
When the engine is cold - pressure is high..
Oil and filter ( Motorcraft ) are new.

Any ideas what i should check ?
Thx

[jhv48]

Is that at idle or at speed. What rpm?

[cycleguy55]

20 PSI at idle when hot is not something to be terribly concerned about, IMO. 20 PSI at 4,000 RPM, OTOH, is an issue - hot or cold.

[bobcowan]

If that's idle pressure, I wouldn't worry about too much.

If that's operating pressure, I'd worry. Probably loose/worn bearings. What "weight" of oil are you using?

[DAVID GAGNARD]

When cold,your oil pressure will always be higher than fully warmed up oil....after your 30 minute ride, your oil temp should be in the 180 to 200 degree range,hot and thinned out,so it flows better than cold/thick oil,hence the lower oil pressure.........

20 psi with hot oil at idle is fine..........

As long as your oil pressure comes up with rpms,say to at least 40 psi or more, I wouldn't worry about it........

david

[datsun280z]

Thank you all.

20 PSI at idle, while driving it's around 40 PSI.
I am happy to hear your opinion that it's normal.

The problem accures when the engine is hot and in idle.. the
engine starts to vibrate ... even strong vibrations until it shuts down

Fuel filter in new, air filter is OK.
I cleaned the Carburator with spray.. looks new..

When the engine is cold and in idle.. it does not vibrate

[genolan]

AT idle what is your RPM reading? It may be to low causing the engine to vibrate and shake then stall. I have to keep mine at 850 RPM.

[bobcowan]

[quote=datsun280z;1343487The problem accures when the engine is hot and in idle.. the
engine starts to vibrate ... even strong vibrations until it shuts down
[/QUOTE]

Bump your idle speed up a bit. The book says something like 650rpm's. But that's for a bone stock engine. Aftermarket heads, cams, carbs, etc, usually require a higher speed. I'd go to 850-900 and see what happens.

If you're running something rediculous like a Holley Dominater and a Victor intake, you might have to go to 1,100-1,200.

[mikeinatlanta]

Idle oil pressure is essentially irrelevant. This link is a great read on oil. Later in the article it discusses how to pick the correct weight oil for your specific motor. Assuming there is no mechanical damage, you essentially pick a hot weight based on oil pressure at a certain rpm. Very informative.
Motor Oil 101 - Bob is the Oil Guy - Bob is the Oil Guy

[datsun280z]

I'll raise Idle to higher speed... it does sound a little bit low..

Thx