# Strange Oil Pressure Issue



## Mitchell Waske (Dec 5, 2018)

Video Link below. What would cause my oil pressure to fluctuate like this? Constant cruising speed it will drop almost in a timed pattern. 400 Pontiac block stroked to 460, Solid roller cam. Wix Oil filter and I know the Filter bypass in housing is plugged.(I didn't do it) VR1 20w50 oil. I have already tried another mechanical gauge both autometer. Same result. Pressure taken from oil filter housing. 4an braided line. I have only had the car for 2 years and have put a good amount of street miles on it. Has always been doing this so I do not think bearing issue. Oil pressure rises with rpms quickly. Cold oil pressure at idle is 60psi +. When fully heat soaked I am getting 20psi in neutral and around 10 in gear. I am looking for input before I pull the motor out. Thanks.


----------



## PontiacJim (Dec 29, 2012)

Why 20W-50? 15W-40 should be all you need. Oil too thick can cause issues unless your bearing clearances were set up loose from the get-go.

20 psi at idle is OK, 60 above 2,600 RPM's is Pontiac's rating for the oil pressure.

I would first go with a conventional oil like Rotella *T-4* 15w-40, or Brad Penn, or .......

If no change, then I would install a new filter housing without the bypass plugged.

I would tap my oil pressure off the small port at the top of the block next to the distributor if you can get the hex plug out. This provides a more accurate reading on oil pressure going to the engine.

You could have a bad oil pump or the by-pass within the oil pump is stuck slightly open with some debris under the ball not allowing it to fully close and oil pressure will fluctuate.

Could be excessive or worn bearings, possibly wrong tolerances.

Oil pickup tube could have fallen off? Or too close to the bottom of the oil pan.

You can try a few things above to see if that will solve anything. But if not, it is typically better to pull the engine and inspect it before you run into a major issue that could have been a simple and inexpensive repair/fix.

So kinda hard to pinpoint such a problem as it can be several things.


----------



## Lemans guy (Oct 14, 2014)

Agree with PJ, first thing is to try a thinner oil, 10W-40 or 10W -30......I use 10W -30 Amsoil ZROD for my flat tapper cam......but you have a roller.....


----------

