What would cause the oil pressure to drop on 454 when you go above 4000? At idle warm pressure is 60 and you accelerate it goes up to 75. Then all of a sudden it drops to 20. Slow down to idle and it will build bac up. Oil cooler is piped correctly.

Could sender be faulty?
If the engine is starts to run hot will that affect the oil pressure? (seems to happen when the engine gets to 180)
Filters have been changed
20w-50 oil
Not sure how long the problem has existed
Would the pressure valve in the boss that is mounted on the engine cause this?
Stock pump

hotter the engine/oil, thinnner the oil=lower pressure. But if oil pressure climbs to 4000, then drops, Im gonna guess the pickup in the pan is starving for oil. Could be caused by too powerful of a pump, small oil pan, low oil level, gunk built up in the heads not allowing oil to return to the pan fast enough.

A number of things could be wrong here.

Is this a twinn? On a twinn if you lose or have a bad ground wire on one alternator you can get erroneous readings from you guages.

Sender or guage could be bad. Put a manual guage on and check the pressure when running.

Oil pick up. Oil pick up could be broken, cracked. or just plain dropped off. Manual oil pressure guage will help with thisdiagnosis.

Regardless, there isn't enough information here to help diagnose the problem. One thing is for sure, if the oil pressure is really dropping off your motor will be short lived if you continue to run.

Good luck, I hope this helps.

The first thing I would suggest is to pull the oil filter and cut it open. I had a similar problem and found that while my oil filter did a great job of filtering oil it did a horrible job of letting the oil flow at high RPMS, it was all twisted and disfigured inside, which in turn restricted the flow at speed. Remember 4000 RPMS isn’t much to us but most of the filters out there were designed for cars and they will rarely run 4000 RPMS for any amount of sustained period of time. I also noticed a drastic change in my oil temp while I was running this filter. Do you run a oil temp gauge and if so have you noticed any difference in oil temp?

When I originally bought my boat one engine did exactly this. Turned out it was missing the windage tray when the shortblock was installed. Wiped out the engine before I figured it out.

BT

Very possible. He says he dont know how long its been going on. Has the engine been rebuilt to your knowledge?

dj,
A quick test would be to put a couple of extra qts of oil in the pan. If that helps the problem, then the pickup is probably getting air for some reason or another. A lot of the oil ends up in the top of the engine while it is running. Also, are you sure that the dipstick is correct ? If the pan has been changed, the stick could be wrong and you just dont have enough oil in it.

Try not to run it too long with the extra oil if it does not help the problem.

The bypass valves should not cause this problem.

Hope this helps,

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Pan was changed, not sure if it has the right dipstick. I see that the 88 420's listed 2 different oil pans and dipsticks. Maybe this is the problem,

When I had this exact problem it was due to too much oil in the pan. Milodon called for ten quarts it was actually eight. Foamed the oil each time at any high RPM and would recover when back down under 4000 or so. Too much oil?????

How much oil on the dipstick is to much? 1/2 inch above the dipstick? Both motors are about 1/2 above the dipstick and only one motor has a problem.