Fluctuating oil pressure.

[lhearold]

My magnum based 408 stroker has an oil pressure fluctuation. At idle (about 850 RPM) it appears to be around 2-4 LBS per Sq Inch and relatively quick. Has great oil pressure 45 Lbs at idle warm and aroud 80 at 2000 RPM. The fluctuation increases in speed off idle and appears to go away at around 1800 RPM but maybe its just fluctuating too fast to notice. Its a new mechanical guage. Changed that first thing as I thought it was a guage problem. Engine is new, only about 200 miles on it. No noise in anything, no leaks, no mixing of liquids anywhere. Idle is not smooth but at about 1400 RPM and up it smooths out so I know its not engine RPM change. Melling hi volume oil pump, Kevko 6 qt pan and pickup.

Anyone ever see anything like this? Any ideas?

Thanks,

Larry

 

[Max340]

Is the relief valve in the pump operating correctly?

 

[lhearold]

A defective relief valve would show consistant low or high not a fluctuation. Oil pressure is fine other than the fluctuation.

 

[fishy68]

A defective relief valve would show consistant low or high not a fluctuation. Oil pressure is fine other than the fluctuation.

Maybe and maybe not. A totally stuck relief valve would do what you say but if it has just a little bur that makes it hang up momentarily it could do that. I gotta say that's a tremendous amount of oil pressure for a regular street car. Your actually wasting HP having oil pressure that high on a street car. Plus some oil filters that have a oil bypass valve in them and they'll actually bypass oil when the engine is cold cause the pressure is so high. That is bad of course.

What weight oil are you running in it? If your running straight 30 or heavier you can probably get it down easily just by switching to 10w30. Just my thoughts.

 

[lhearold]

I was running Shell Rotella 15W-40 as that is what the builder recommended for breakin but I changed to Castrol GTX 20-40 yesterday since someone said that the Rotella might be foaming and causing the problem. Didn't make any difference though. Most of my engines have always been built for that pressure. I imagine once its run in a while it will change some (lower) so at present it doesn't present a problem in itself. I guess it could be the valve in that respect. I just figured that even a bur would cause a partial stick open.

As an after thought, My 98 Durango S/T 5.9 has 40 Lbs idling and 75 at 2000 RPM (mechanical gueage not factory) so the pressure isn't too far off the factory.

Larry