Newcomer to the OSO forums. Been lurking around for about 3 months now... you have a wealth of knowledge on this forum! I've searched high and low and I can't find a 100% answer but I think I'm getting close. Wanted to see what the 'experts' thought.

anyways picked up a '96 26 Scarab /w a custom built 540 stroker and b1 xr mid-summer. Motor had about 25 hrs on it and was built in 2016 per the previous owner. I have the motor invoice and parts list but it's not too detailed (see attached). Took it for a test run before pulling the trigger and everything seems fine, oil pressure at cruise was good (40psi), water temp about 150 so on and so forth.

Put about 10hrs on it over the last few months and unfortunately sucked some mud/sand on my last trip and over heated the motor. Water temp was pegged at 212 which I think means I was getting some water into the system but it was boiling off. Had no choice and had to limp home @ idle for over an hour. burned about 1qt of oil in the process but the motor sounded fine. Got it home and tore the water system apart and surprisingly the impeller was fine (changed it anyways). Back flushed the lines and a ton of mud/sand came out of the oil cool so I imagine that's where is clogged up. He used conventional vr1 20/50 but I wanted to switch to the synthetic version for the oil change. new filter (HP4) and put 8qts into the system (1 in the filter + 7 in the pan). As far as I can tell it's got an 8qt pan and a stock merc marine 805567v dip stock which I believe is for either the 7.4 or 8.2 blocks i.e. 8 qt pans. So here is the issue. Oil pressure was 50psi idle cold and 75psi idle warm. Anything below 3K rpm would hold 75psi, but anything above and it's start dropping quick. At 4K I was seeing less than 20PSI and WOT the needle was just bouncing off 0. Put another QT of oil into the system so now that's 9 total, good improvement. At this point the dip stick is reading a hair over full cold and a good 1/2 inch over hot. Pressure holds stead at 75PSI all the way to 3900RPM, at 4K to 4400 I'm seeing 40-50PSI and WOT is hovering right around 20ish. No signs of foaming of the oil when I check after a run. Does this sound like I'm pumping the pan dry? I have to assume it's a HV pump based on the high idle pressure. Should I try another 1/2 QT at a time up to 9QT's in the pan + 1 in the filter + hoses and cooler? The only other data point I have is the water temp is much lower than it was previous to back flushing. It barely gets over 120 even after a hard run. I'm in the Delaware river so water temps are around mid-60's. It has a bypass without a tstat.

Your oil pressure is all over the place. Prior to overheat cruise is 40, then after overheat 50 cold and 75 warm
Install a mechanical gauge and see what pressure really is

Pull thermostat and test in a pan of water on the stove or get another

I'm ammazed your motor is not totally trashed idling back for an hour with next to no water flow

Could I put a mech gauge on a plugged port on the remote filter mount or better off closer to the motor?

You could, but the best place is port side low, where the oil pressure sender is. Just remove sender and install mechanical gauge, or better yet get a Tee and install both at same location. You want to know what the pump is putting out. Installing on the filter could give same reading if there is no issues with other components. You want to know if your gauge is off or is it the motor

Not running a tstat so it could just be that there is way too much flow (water) now that I've back flushed it.

I was surprised myself but the motor shows no signs of issue other than the low oil pressure at WOT. If I punch the throttle for 30-60 seconds it revs up to 5k and hits 70mph no problem which was what it was doing prior to overheat and oil change.

I will do a leak down/comp test when the season is over just for giggles.

Awesome. Thanks for the advise. Off to Amazon to next day a mech gauge

Its best to have a thermostat in because it keeps the block full of water. Without it, it can get a air pocket and cause hot spots that may not show up on the temp gauge

I don`t know too many with blower motors that run stats. I have no problems with any "hot spots" . Pretty sure at 20 psi the block is full of water. No thermostat to stop that flow.

Your probably right, but what about lower pressures like idle when its at 2 or less?

Could be sucking pan dry, foaming oil/no windage tray, or sucking filter shut...

Also do you have oil temp gauge?