Have a 402 bores 60 over .. Cold oil presure is at 40 psi. When it warms up its at 25 this is at idle . Cruising speeds it is at 45 psi . Is 25 psi too low at idle for a rebuilt engine . I only have run this engine about 10 times for short trips to gas station ect...ect..

You have plenty of oil pressure. There is nothing to worry about.

Just wondering when to be concerned . At idle what would be dangerously low psi ? I just cant beleive the difrence in oil presure from cold to hot .. Why does it start cold at 40 psi then warm up and drop to 20-25 psi ? I would think a rebuilt engine would stay very constant ,but maybe Iam miss informed .

General rule of thumb is 10 psi per 1000 rpm. I'd be nervous with less than 15 lbs at idle, and less than 25 at anything over 2500. Yours sounds typical of a stock engine-most folks are used to the hi pressure pumps and the hi readings they give.

As to why, when your oil gets hotter, it thins out. Thinner oil is easier to push, so then you get less pressure. Plus, as the engine warms up, I'd assume clearances my increase slightly due to expansion, again, more clearance, less pressure. My .00002 and some quessing. I'm sure if I'm wrong someone will correct it smile.gif

Thats not too bad for a stock engine. I know a lot of guys here dont like high oil pressure and would tell you that it is enough for a hp motor. I'm from the old school and like high oil pressure on a hot rod engine. If you are still worried try running some 20/50W oil if your not already, but I wouldnt be concerned.

Yeah, I don't know why people strive for high oil pressure...I guess it is supposed to equate to ultra performance or something. I saw a post just a couple of days ago from a member who broke part of the oil pump drive line running 100+PSI with 20W50 oil :eek: If you want it super high, just plug all the passages!

There is a happy medium with the pressure. Sounds like you have nothing to worry about.

Thanks guyz you put me at ease !!! smile.gif