Engine smoke and oil pressure question

Egor

Egor

Member
Jul 22, 2023
51
Monterey Bay, California
Boat Info
SeaRay 340DA 1999
Engines
Twin mercs
Hello,

I have SedRay 340DA with twins Mercuisers 7.4 MPI 1999

Oil is about 1 year old. Oil levels are fine. Oil looks clean, not darkened, no particles. In both engines.
I also noticed that starboard engine consume more fuel than portboard engine, on RPM 3000 and above

Two quesitons:

1 when running above 3000RPM I obtain some amount of exhaust smoke. Is that normal? (I have a lot more pictures and videos if needed)
View attachment 152672

2 Oil pressure gauge readings on two engines are different: Port board stay still at 40PSI, while starboard is ~~30 PSI
View attachment 152671


and yesterday after running at 4000RPM I noticed it drops to ~~25PSI.
View attachment 152670

So the question is is that normal? what may cause it and where I should start and how to process with research?
 
Exhaust is probably normal based on water and air temps.

Oil pressure could be several things. I would start with maybe swapping the gages and see of the readings follow. Then move to the sending units. Basically rules out the easy stuff. I wouldn’t worry too much unless it goes really low. I think spec is 20-40 or something like that.
 
Rule of thumb is 10 psi oil pressure for every 1000 rpm. Your first picture almost looks more like steam than smoke; what was the air temp when you took that picture?
 
Yup, picture 1 is steam or just warm water vapor vs: cold air.
Don't bet the bank on the instrument cluster gauges to be 100% accurate on the oil pressure. They can be off, too. Verify w/ a mechanical gauge to ensure the accuracy.
 
I had a strange drop in oil pressure at elevated RPM's a couple years back. It turned out I had a very small leak in one of my remote oil filter linesets. Easy repair but finding the dang thing was not so easy.
 
From what you've posted, nothing sounds out of the ordinary. Spec on the oil pressure is something like 5 or 6 psi. But of course, that doesn't mean you want to run the engine that close to spec.

What's more important are "trends". Different engines can run happily for many years at different gauge readings. Now, if all of a sudden things change - then that's something to investigate. But if it's been like this for a long time, I wouldn't worry about it. As noted, though, you could swap the senders... and even the wires to the senders in there original spots (lengthen them) to eliminate some variables.
 
Do the engines sound normal or are you hearing any tapping noise from engines. Best bet is check with a mechanical gauge like said above
 
We have fuel flow gauges on both engines. The Starboard reads 1GPH more at 1600 RPM and 3 at 1900RPM and 10 at 4000RPM but when I fill the tanks they take the same amount. Oil pressure on Port is 65 to75PSI and Starboard is 38 to 45PSI on upper helm on lower helm it is lower. Point is I do not believe the gauges. I did change out the pressure transmitter on the Starboard once and pressure dropped. As many have said the only way to find out the real pressure is to use a real gauge. Neither engine uses oil between oil changes. Engines have 3,500 hours on them.
 
It could be as simple as a oil filter that's not functioning properly
 
Scott215 said:
Do the engines sound normal or are you hearing any tapping noise from engines. Best bet is check with a mechanical gauge like said above
Click to expand...
I think they sounds normal. As much as I can judge, as I am not expert.

I dunno if it is normal, but above 2000 RPM engines become noisy and above 3000 very noisy and it feels like whole body is resonates
 
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