Since the engine rebuild and oil cooling upgrade last year there has been some strange oil pressure gauge fluctuations.

At idle, oil pressure is normal @ 40 psi.

At cruise, the oil pressure is centered around 55 psi @ 2100 RPM, but the needle flutters +/- 20 psi so fast that the needle is a blur.

Under coasting conditions, the needle fluctuations are less (+/- 10 psi), but still very apparent.

Here's a list of the before / after changes:

Changed the stock gauge feed plastic tube to a -3AN. The guage is a stock GM console gauge.
Oil pump from HVHP to Mellings 555
Elimination of the oil bypass to allow for CV Products oil filter adapter (no bypass)
Addition of lines and fittings for cooler (several unwanted, but needed 90*'s)
Addition of remote oil filter mount.
Addition of an in-radiator oil cooler.
Milodon 5 qt pan to CV Products 8-quart road racing pan
CV Products oil pan pickup.
Engine rebuild included new main and rod bearings.
10W-30 to Mobile 1 15W-50 synthetic.

The engine runs great, has no funny noises, and during oil changes there have been no abnormal particles.

Fatigue life of the gauge is a concern since I'd hate to have the gauge fail in the car. The other is if there is a high-frequency pulse in the system, what will it affect? Fatigue of the in-radiator cooler? Oil film thickness? etc.

Any ideas would be great.

Thanks.

First event on the agenda I would do is to bleed the oil line. Second would be to substitute a different gauge of better quality, Autometer, Stewart-Warner, etc. and see what it indicates.

If it still fluctuates, I'd look at the timing marks to see what they are doing, are they fluctuating as well.

If the timing marks are not steady, then I would suggest removing the oil pan and pump. Remove the spring and its plunger and polish the plunger with emery paper and reassemble all. Its intense, but, it worked for me.

If the timing marks are steady, and the reference gauge still fluctuates, visit a Hydraulic & Pnuematic supplier and get a gauge dampener and install on the oil line. McMaster-Carr has them also.

It was fine prior, right? Have you put a guage on the pressure port on the rear of the block to recreate (assuming it will do it at standstill 2000 rpms's)? The 90 degree bends strike me as a culprit. Any alternatives?

New gauge already on the way.

I'll try bleeding the line, good idea.

Timing does not fluctuate.

If the new gauge + line bleeding do not work I'll try re-installing the stock filter adapter. This will eliminate the hoses and cooling system from the loop.

Getting rid of the 90's will make hose routing really fugly. It's the last resort if everything else does not work. At least the 90's are the tube type, not drilled.