High Oil Pressure 4.3 Carb Mercruiser

I just changed the oil and filter on my '05 Stingray with 4.3 and Alpha 1 Outdrive which has been out of the water since November due to low lake levels.
I ran it on water ears up to 160 degrees from idle through 2000 rpm just above 50 psi but the oil drain was very slow. Ran it again up to 180 degrees and the oil drained OK.
Chaged the filter and used Mercury 25W-40 (Same as I drained out) When I put it in the water it ran great but the oil pressure was around 180 psi at 3000 rpm (around 45 mph). I thought that the new filter non marine filter (an AutoZone Mercruiser replacement) might be restrictive and installed the larger marine one that I had removed. Same result except that after a few minutes of running, it came down to the 170 psi range.
Anyone got any ideas?

 

What do you mean the oil drained slow? and then the oil drained OK?

How do you know it was 180 PSI? do you have a guage that reads that high?

Are you saying it was ok before you changed the oil?.

Is it electric guage or mechanical?.

 

The Stingray 195 has a drain extension that is accessed through the hull drain plug. When I opened the oil drain the "dribbled" out very slowly. When the engine was run until it reached 180 (water temp) the oil drained normally. The oil was only slightly colored which is not surprising since it only had 10 hours of running last season.
Yes the gauge indicates up to 180 and the needle was just shy of being pegged @ 3000 rpm. On the water ears, I got up to 2000 rpm (old oil) and the gauge indicated 150 which is normal for the boat until it has run for about 10 minutes when it comes down to 40 psi.. I didn't run it at cruise speed on the ears since I was only warming the oil for draining.
The gauge is electric with a pressure sensor in the block adjacent to the oil filter.

 

That is high oil pressure and Im surprised you hav'nt split the oil filter.

I would swop your sender with a new one or borrow one from your car and make sure that reading is actual. If you can fit a temporary mechanical guage that is better.

If these cold readings of over 150 are true then it is your oil pressure relief valve that is not working and is there to do this job of releasing high pressure when cold.

I am not familiar with your engine but an oil relief valve can be external on the block or sometimes in the filter housing with sender unit.

Or if your unlucky they are in the pump needing engine out.

Firstly find out what your oil pressure should be and confirm your readings.

 

Frosty
I gave you bad info and didn't catch it even when you pointed it out in one of your questions. I confused my oil pressure reading and water temp reading when writing my post.
I should have said my gauge reads 80 psi not 180.
You are right, 180 would have blown the oil filter.
Just spoke to a friend who is a GM mechanic who said that the gauge sending units frequently go bad if the engine is laid up for a time. Like you he suggested a cheap mechanical gauge to use as a test. Also said that he has seen many gauges go bad due to poor stepping motors in the gauge head. Although he has heard of bad pressure release spring and pin (in the oil pump) he has never seen one in his 20 years as a GM mechanic.
Sorry about the bad info and thanks for your help.