Just picked up a 1997 Donzi 22 ZX with a stock 454 Mag. Engine hours are estimated to be around 350-400 (no hour meter). Took it for its first run this past weekend and everything worked well, however I'm used to seeing higher oil pressure numbers (my experience is mostly with performance car engines). I'm getting the following:

Cold idle - 40 PSI
Cold 3000 RPMS - 45 PSI
Hot idle - 15-20 PSI
Hot 3000-4500 RPMs - 40 PSI

Idle pressures seem normal but the motor will not make more than 40-45 PSI regardless of conditions. Just wondering if this is typical of these motors, almost seems like the pressure relief spring in the pump is set to 40 psi? I did a little research on the forums and see mention of a 30psi bypass valve, is this a worthwhile mod to add just to be safe? Should I be concerned at all with these numbers?

Thanks.

I have 454 mag mpi's in my '98 and both engines have similar oil pressures for as long as I have owned the boat.

Hot idle 20 PSI
Hot 2500 rpm 40-45 PSI

Mercruiser Service Manual # 23 Specifications for 454 and 502's

Oil Pressure (at 2000 rpm) Minimum 30 psi
Min. Oil Pressure (at idle) Minimum 4 psi

I know these numbers seem low but that is what the Merc Book states is normal. I now have over 500 hours with no problems, I think it is the nature of the beast.

That is about the same as my 502mpi's.

If the engines are EFI's, then they can be scanned to determine actual hours.

Yup, sounds normal.

Also, my 496HO reads about the same as my 454 Mag read on the oil pressure guage. But, when I do a Diacom scan, it shows about 10 psi higher than the guage.

Right on, you guys made my day. Unfortunatley this mill is carb'd so I think I'm SOL on the hours. Just made me a little nervous since I'm used to seeing 60 psi max or so out of my cars with chevy motors.

Would the 30# bypass valve still be a good move or just a waste of time?

Don't bother, it's fine.

my almost new now gen VI 454's carry about 40-45 at 3k or so warm...been that way since put them in..chevy's do not require tons of oil pressure to live..don't run any more than this with my 565 sonny's drag race engine..

I have a 2001 454 MPI MAG and my pressures are almost exactly the same as yours.