Hi oil pressure at 3000rpm. Should I do an oil flush

[jdklein001]

Well, the title pretty much says it all. I have 1998 mercruiser 4.3 vortec’s. (Sn 0L020379). The guy I got the boat from, end of last season, put them in about 10 years ago and only put 45 hours on them. I’m not sure if that was 2 hours a year or if the boat sat unused for many of those years.
I had a chunk of riser break off and destroy the impeller on one engine and am replacing all of the risers/manifolds.
on the engine that didn’t happen to the oil pressure rises to the around the top of the gauge once I hit around 3000 rpm. The pressure gauge I got last year to test at the engine was garbage and didn’t work.

Do you think doing one of those oil system flushes would possibly help?

 

[alldodge]

the oil pressure rises to the around the top of the gauge once I hit around 3000 rpm

How much pressure is at the top of the gauge?

Suggest a mechanical gauge for testing

 

[Bondo]

Ayuh,..... Extreme oil pressure is expected in a stone cold motor too,......

 

[jdklein001]

The gauge on the dash does not indicate number, just high and low.
This is happening when the engine is warm, I’ve never revved it when cold.

 

[alldodge]

I doubt there is a problem, but to know for sure remove the oil sender and install a hand held mechanical gauge. Can probably get a loaner at a local auto store

 

[Lou C]

I would be checking the gauge and sending unit, doing a flush is risky because if there is sludge it could turn it loose and clog the oil pump screen starving the bearings. Just change the oil and use a good filter; I’ve used both Sierra and Merc filters and never had issues with abnormal oil pressure readings.

 

[Bt Doctur]

I had a chunk of riser break off and destroy the impeller on one engine That just not possible

 

[jdklein001]

New gauge, sender, filter and oil change are in the works. I’ll put her in the water and see how she goes. No flush. If I need the top end rebuilt that will suck be be how it goes.
Can anyone confirm that a top end job can be done with the engine in the boat?

 

[Bondo]

Can anyone confirm that a top end job can be done with the engine in the boat?

Ayuh,..... It's alot more work that way, 'n the top end of the motor, really has nothing to do with oil pressure,.....

 

[alldodge]

^^^^ Agree, you would be wasting money

 

[Lou C]

I did mine that way but I did enough diagnostics to know that it was necessary. In your case you still don’t know if you actually have an oil pressure problem. And what exactly were you trying to explain about the riser (elbow?) and the impeller you lost us all there...

 

[Scott Danforth]

oil pressure is controlled by 4 things.

• the first is the oil viscosity. that will change after time, and with temperature
• the second is the spring on the oil pressure regulator. your oil pressure can never be higher than the spring setting unless the pressure regulator has failed (either a stuck PRV piston, or other reasons). stock spring is about a 60 psi spring
• the third is the amount of clearances in your bearings
• the 4th is the pressure drop across your oil filter.

by the time oil gets to the top end of the motor, there is little to no oil pressure, as the top end oiling is done thru the push-rods, after the lifters. so its essentially system drain oil. rebuilding the top end will not change your oil pressure.

the oil pressure gauge reading is generally controlled by 2 things

• the response characteristics of the oil pressure sender
• the quality of the electrical connections between the gauge and the sender.

generally, a short to ground on the oil pressure sender will peg a gauge

swapping components without troubleshooting simply drains your wallet.

 

[jdklein001]

With the riser/manifold breaking up I was simply trying to illustrate that after the boat sitting mainly idle for the past 10 years (50 hrs of use since the repower with crate motors) that some things had rusted up and that it is unclear at this point exactly what’s good and bad with all of the systems. It had nothing to do with the oil pressure.

I had read that high oil pressure could be a result of a relief valve sticking or a bearing (I thought it was in the top end somewhere but I can’t recall) not working right. Ive also heard it’s unlikely the relieve valve as that shouldn’t be kicking in till a higher psi. If it was the bearing I believe it’s a large job that I’d really try to avoid.

 

[jdklein001]

Scott, I didn’t see your reply until after my last post.

 

[QBhoy]

Hi
How did the rusty bit ruin the impeller on a 4.3 and presumably Alpha drive ?
Anyway...I’d check your thermostat is good to begin with. A cold running motor would show higher oil pressure. Most likely your gauge is playing up though.