Low oil pressure.
 

I have twin Mercruiser 350 custom built to 425hp. This winter my old man and me rebuit one. New crank, bearings, rings, lifters, Melling high volume oil pump, carb ect. Kept the same pistons cause the block was already 60 over. Question is, I'm only getting 25psi hot idle and 42-45 psi at 3500. The other engine is getting 45psi idle and over 55 at 3500. What the heck is going on. Any ideas. Am I about to blow this engine ........again. When looking through the oil cap there seems to be quite a bit of oil splashing around. I also just put 2 new oil senders on.

Chris

Too much bearing clearance or a bad oil pump are common causes. Once I did a motor and neglected to tighten the oil pump bolt. I learned never to allow yourself to be interrupted when doing something important.

Buy a mech gage with copper line and make sure of your readings. I have one engine that reads low continuously but in actually is too high with a mechanical gage (80+ cold). I know this engine is tight because I built them both. Check it with a mechanical gage before jumping to conclusions. If I didn't know how my engines were built I would guess this one is weak and it is not.

25psi hot at idle I wouldn't consider to be bad, and 42-45 at 3500 rpm I don't think is bad, I'm more curious about the other with 45 psi at Idle, is that hot or cold, get a mechanical gauge and check them both, most engines that I see only run about 20 psi hot at Idle and 45-60 at higher rpm's
Larry

I think those numbers are in the normal operating range. Both of my 350's idle at 25-30psi.

I wouldn't be concerned either. Oil pressure is not really what you want anyway, you want oil volume, big difference. Just because oil pressure is high, doesn't necessarily mean you're getting good lubrication.

If you just put new sending units on, try swapping the sending units and see if the problem follows. Might just be a bad sending unit.

new engines , probably new filters ive plugged filters and had oil pressure probs? make sure youre oil lines are run correct also