When I start my motors both motors go to over 70PSI oil press and then when they are warmed up they are hovering a little over and a little under 20PSI.....is this normal????? Also when running the boat hard my oil temps come up to between 250-280 with the sender in the oil pan. Is this ok????

You might get better response if you move your thread to the TECH Forum.

The first question everyone will ask, Did it just start doing this?

280 is getting on the high side for oil temp. I don't let mine get over 250 after a hard run. Usually stays at 210 at cruise.
Oil pressure starts at 70 and drops to 50 at idle and never lower than 40 at ile after a hard run. I still think my pressure is high, but it has stayed togethere for three years now.

I bought the motors this winter, tore them down and they have just been put into the boat......

Big block needs the better part of 50psi running hot to live.

Around 20 PSI at idle with warm engines sounds low. But what oil temperature do you have with warmed up engines when you see the 20 PSI ? Is that with temperatures in the 250-280 range ?
If you idle for some time after a hard run do the oil pressure then increase ?
What type of oil are you using ?

Yeah 20PSI is when the engines are at 250-280, and I am running Joe Gibbs 10W 30 hot rod oil in them cause they are flat tappet with solid lifters.....

How long is that 10w30 been in the motors?i assume you were using that oil for break in?10w30 is too thin for a marine application for final use,if you were to use a 20/50 or 15/40 or thicker oil you would lose the pressure problem and maybe temp problem,i ran 10/30 through my motor for 45mins,then went to 20/50 for about 10 hours,then went to 20/50 royal purple,my oil pressure at start up is about 75-80 psi and 50 when hot,oil temp is about 190 when run.what thermostat temp do you have in them?

140 for the water temp. no therm on oil....what oil should i use for those motors????

Those numbers sound reasonable, try running Mobil-1 v-twin 20/50 and you will see much better hot idle numbers.

This is a full synthetic intended for Harley's which are notorious for cooking regular oil.

I have been running it for nearly 8 years.

BTW it will be fine with your flat tappet cam, I ran it in my jetboat after break in. No problems at all.

Joe Gibbs is a racing oil and probably does not have the detergent properties or the wear additives that are ideal for a marine v8.

BTW Mobil-1 also recommends v-twin for marine use.

280 is too hot and if you are running a conventional oil you are risking engine failure. Even with synthetic you are shortening your engine life. No question the high temps are causing your low oil pressure. You likely need larger oil coolers but first I would check to see if you aren't running lean carburation. Also here is a good thread on oil pressure and plumbing. http://www.offshoreonly.com/forums/s...3&page=1&pp=20