Need info on 251 engine

[Alex Blair (RIP)]

Originally Posted by Alex Blair

Micheal..This is normal for the oil pressure to drop back after warming up..
and it will go down after warming up and will fluctuate with changes in RPM..
My old flat heads would start out cold at 40-50 PSI and drop to zero pressure at an idle warm..If it bothers you..put a piece of tape over the gage ..so you can't see it ..Sounds normal to me..

Mike..
If you start at 45 PSI cold and you drop off 15 PSI..even 20-25 PSI..that would still be lots of oil pressure..hot..15-25 Psi HOT IS OK..YOUR OTHER TWO ENGINES MUST HAVE BEEN REBUILT AT SOME POINT..

You may want to change your oil over to straight 40 Weight..non detergent oil..That was the summer weight oil that it was designed to use..Multi grade detergent oils were not even invented when that engine was designed..
It wasn't until 1968 that Castrol came out with it's Castrol GTX 20-50Weight multi grade that multigrades came into play..
And then they cut back on the zinc and phosphorous as anti wear additives when the catalytic converters came in so there are a lot of changes in motor oils since the 251CI came into being..Go back to the oil that was designed to run in it and enjoy it..

That is if you drive it only in the summer..you could drive it when it was cold but may have to plug it in to warm the oil before starting..Even with 40 weight ,non detergent oil in it you will see some drop in pressure..
That would quiet your engine,not drop as far on the oil Gage and work OK ..But the engine may be getting a little tired and a new set on main bearings and a regrind on the crank ,if it needs it ..but I wouldn't worry about it and drive it like it was until you decide to rebuild it..
Enjoy it and don't worry about it..
BUT..if it still bothers you..change the oil guage..It is probably worn out and will flicker and vibrate and do all sorts of tricks..it would be my first step ,if it was mine..