High oil pressure 4.3mpi

[blaster]

I have had a high oil pressure condition with my motor since last season.

I perform maintenance according to mercury recommendation in the manual for saltwater use. So, oil change every 50 hours with mercury oil and filter, idle air muffler, clean flame arrester, and so on.

I brought it to PWM and they suggested I replace the oil pump. They put a mechanical gauge on it and got 80 psi at idle. They also checked compression and one cylinder was low, around 125 psi but the boat had been sitting a while so I wasn’t convinced when I was told the solution was a new oil pump. They suggested it would be better to replace the engine with a long block.

While I appreciate their knowledge and how they planned to fix my boat it just doesn’t seem right that a religiously cared for motor would have this issue before 600 hours. I told them I will replace the motor after it blows up and I get towed home, or sail and row.

I brought my boat home and the first thing I did was change the oil and filter. I added a half quart of marvel oil to the mix. Then I did a tune up. The plugs were fine with normal wear. I replaced the wires, cap, and rotor. The rotor had a crack in it, uh oh.

Took the boat out and ran it for a couple hours. Oil pressure was normal around 40 psi not the pegged 80+ I was getting before. At idle though the oil pressure was almost too low barely reading on the gauge. I just assumed it was from the marvel lowering the viscosity of the oil.

After my run I changed the oil again and used straight mercury 25w40 and the oil pressure at idle returned to normal.

I believe I had a bad oil filter which caused the high pressure condition but I’m not sure.

During my research of this issue I have found that this has happened to multiple mercury 4.3 and 5.0 engines. Most responses to this problem say “just run it. High oil pressure is better than low oil pressure”. I disagree, there is a reason this is happening. I have not had the problem since I did the tune up and the two quick oil changes.

I feel like three things could have happened.

(1) the oil filter was defective.

(2) the oil pump has a sticking pressure relief valve.
(3) there is something blocking oil flow within the engine.

What ever it is, I hope it stays away. I’d rather not re-power my boat yet.

Has anyone come to a conclusion regarding high oil pressure in these mercury engines?

I can’t figure out what caused it, why it went away, or whether it will re-appear.

any thoughts or possible other causes for this would be helpful.

thank you.

 

[techmitch]

I have had a high oil pressure condition with my motor since last season.

I perform maintenance according to mercury recommendation in the manual for saltwater use. So, oil change every 50 hours with mercury oil and filter, idle air muffler, clean flame arrester, and so on.

I brought it to PWM and they suggested I replace the oil pump. They put a mechanical gauge on it and got 80 psi at idle. They also checked compression and one cylinder was low, around 125 psi but the boat had been sitting a while so I wasn’t convinced when I was told the solution was a new oil pump. They suggested it would be better to replace the engine with a long block.

While I appreciate their knowledge and how they planned to fix my boat it just doesn’t seem right that a religiously cared for motor would have this issue before 600 hours. I told them I will replace the motor after it blows up and I get towed home, or sail and row.

I brought my boat home and the first thing I did was change the oil and filter. I added a half quart of marvel oil to the mix. Then I did a tune up. The plugs were fine with normal wear. I replaced the wires, cap, and rotor. The rotor had a crack in it, uh oh.

Took the boat out and ran it for a couple hours. Oil pressure was normal around 40 psi not the pegged 80+ I was getting before. At idle though the oil pressure was almost too low barely reading on the gauge. I just assumed it was from the marvel lowering the viscosity of the oil.

After my run I changed the oil again and used straight mercury 25w40 and the oil pressure at idle returned to normal.

I believe I had a bad oil filter which caused the high pressure condition but I’m not sure.

During my research of this issue I have found that this has happened to multiple mercury 4.3 and 5.0 engines. Most responses to this problem say “just run it. High oil pressure is better than low oil pressure”. I disagree, there is a reason this is happening. I have not had the problem since I did the tune up and the two quick oil changes.

I feel like three things could have happened.

(1) the oil filter was defective.

(2) the oil pump has a sticking pressure relief valve.
(3) there is something blocking oil flow within the engine.

What ever it is, I hope it stays away. I’d rather not re-power my boat yet.

Has anyone come to a conclusion regarding high oil pressure in these mercury engines?

I can’t figure out what caused it, why it went away, or whether it will re-appear.

any thoughts or possible other causes for this would be helpful.

thank you.

It wouldn't be the first time I've seen an oil filter being the root cause of excessively high oil pressure. Or 2nd or 3rd time.

 

[aerobat77]

i had it once on my 5.0 mpi . there is a small and large oil filter , both will physically fit but the large one resulted in high oil pressure . replaced the filter with the smaller one and everything is nice again ( 50-60 psi in cruise ) .

i agree an excessive oil pressure is asking to wreck the oilpump or blow anything else .