Different oil pressure in 4.3 Mercruisers and some other questions

[pmp1986]

Hi, friends,
Going on with my engines problems (4.3 Merc 96 year SeaRay)
When idle left engine show 4-5 psi on oil pressure meter, but right one (which was completly repaired this season) less then 2 psi.
Also checked compression (mechanics said that i need time to get right numbers after repairment) and it's from 6 till 9,5 on right and 11-12 on left engine (which not repaired at all).
How bad is this? Might be engine wasn't repaired completly as said?

Also i've taken a look at propellers (they are some kind of aftermarket as previous owner said). Does anyone know whats correct size of propeller for alpha drive with this engine?

Best Wishes

 

[Scott Danforth]

Check the oil pressure with a good diagnostic mechanical gauge. That oil pressure is dangerously low if accurate.

What are your compression numbers? should be about 140- 150psi per cylinder with about a +/- 7psi variance

 

[alldodge]

The minimum oil pressure at idle by the manual is 4 psi, that said I have never seen one at that pressure (using an accurate gauge) which didn't have problems. Both reading about the same I would check voltages, connections and grounds. If there is a bad ground the resistance will be higher and the gauge will read lower. Best way to verify is install a mechanical gauge on the oil pressure port. Also with it being that low is there an alarm going off?

Also checked compression (mechanics said that i need time to get right numbers after repairment) and it's from 6 till 9,5 on right and 11-12 on left engine (which not repaired at all).

Are you saying 6 to 9.5 is BAR so that would be 87 to 137 PSI? If this is PSI then its real bad

For a fresh rebuild this is an issue, I would expect to see closer to 150 PSI. If it was a full repairment (overhaul) then something was not done correctly. Could be rings, valves or was not done at all. Does it even start and run?

Don't know which prop should be there but I'm thinking about a 19 pitch

 

[pmp1986]

The "problem" is that no alarm at all. During acceleration (3500-4000) left engine show max oil pressure, but right show 3,8-4 at the same rpm.
Thx. for advice - i'd do so, but i don't know where it's located. Might be some picture or description?

I'll check tomorrow what's that scale mesure is (but it's in red part for the left engine).

Yeap. It's start and run. Both. Max. speed is 45 km/h

 

[alldodge]

Might be the gauge, don't know need some testing.
The old pressure gauge sender is the larger one in the pic below (black) the other is the oil pressure switch.

To find out if its the gauge, remove the light blue wire from the sender. Turn key ON, (no need to start motor) and ground the light Blue wire, the gauge shoul peg max pressure

 

[pmp1986]

Checked gauges. They are ok. Smth. wrong with engine. I've checked it's compression with psi scale. It's from 75 to 110 psi. And gauge show low oil presure for this engine. And it starts really hard.
I think I'd have some talk with mechanics on what overhaul did they do... It seem that they did nothing.

P.S. If boat will be used with such oil presure and psi on engine will it result in damaging it very soon?

 

[alldodge]

With compression that low, it will not run very well as you've seen. IF the oil pressure is that low it will damage the bearings and may have already. Need to get a mechanical gauge to check pressure at the oil port