Oil pressure

[Yorkshirelad]

Hi Guys,
Just changed the oil and filter before winter haul out. My oil pressure at 600 rpms on the port engine reads 30psi and starboard engine reads 40.
Running at 3,000 rpm I get 50 psi on the port and 65 psi on the starboard engine. Should I be concerned or assume it’s the sender units and maybe replace both sending units. My Searay EC is 1986 with mercruiser 454 7.1, about 800 hours on each engine still runs strong. Love this boat!
Cheers Rob

 

[Henry Boyd]

Speaking from memory your starboard engine looks closer to what our 496 (8.1L) put out, but the port may still be within acceptable range. The big thing with oil pressure readings are whether the readings are consistent. In other words they weren't higher a month ago. The other thing is that do the readings are steady and don't wobble, i.e. 30 isn't really 30, but the middle of a 27 to 32 psi swing at constant rpm. A change of the oil pressure over time, or reading wobble can be the result of worn bearing clearances, and also a deteriorating oil sender.

What to do next presents a conundrum. To properly diagnose one would pull the sender off the port engine and attach an external mechanical gauge and run the engine. But if you don't have a gauge and adapters, or you would have to remove and reinstall a component like an exhaust manifold, it may be cheaper to just swap out the sending unit. Of there is no change, you've bought a $100 sending you didn't need, but you don't have to re-do the R&R to put the old sender back. Either way this is not something to ignore; a failed connecting rod bearing usually results in said connecting rod explosively exiting the block and trashing the engine block. But the present point your worst case is the engine needs a bottom end job. While expensive it is substantially less expensive than finding, buying, and installing a replacement 454.

 

[DWABoat]

Would it be practical to just run a temporary wire from port to stbd and stbd to port and see if the gauges still run the same?
He could just make some wires using male and female spade connectors. Cost would be a few bucks and take an hour tops.
I do t know if this would mess up some of his electronics. If his boat gauges are from the 80’s, then there are probably no computers. Just EFI.

 

[Yorkshirelad]

Speaking from memory your starboard engine looks closer to what our 496 (8.1L) put out, but the port may still be within acceptable range. The big thing with oil pressure readings are whether the readings are consistent. In other words they weren't higher a month ago. The other thing is that do the readings are steady and don't wobble, i.e. 30 isn't really 30, but the middle of a 27 to 32 psi swing at constant rpm. A change of the oil pressure over time, or reading wobble can be the result of worn bearing clearances, and also a deteriorating oil sender.

What to do next presents a conundrum. To properly diagnose one would pull the sender off the port engine and attach an external mechanical gauge and run the engine. But if you don't have a gauge and adapters, or you would have to remove and reinstall a component like an exhaust manifold, it may be cheaper to just swap out the sending unit. Of there is no change, you've bought a $100 sending you didn't need, but you don't have to re-do the R&R to put the old sender back. Either way this is not something to ignore; a failed connecting rod bearing usually results in said connecting rod explosively exiting the block and trashing the engine block. But the present point your worst case is the engine needs a bottom end job. While expensive it is substantially less expensive than finding, buying, and installing a replacement 454.

Hello,
Thanks for the info, my numbers did increase after the oil change.

 

[Yorkshirelad]

My oil pressure numbers are constant, they did increase after the oil change though.

 

[Henry Boyd]

Would it be practical to just run a temporary wire from port to stbd and stbd to port and see if the gauges still run the same?
He could just make some wires using male and female spade connectors. Cost would be a few bucks and take an hour tops.
I do t know if this would mess up some of his electronics. If his boat gauges are from the 80’s, then there are probably no computers. Just EFI.

Yeah, that might work although these are single wire senders that is part of the engine harness and I don't know if having an unmatched ground and power would have an implication other than both engine ignitions would have to be on for one sender to work. Certainly worth a try.

 

[Henry Boyd]

My oil pressure numbers are constant, they did increase after the oil change though.

Ok, so you have had the same differential between port and starboard for some period of time? If so that means at the least one engine has not recently gotten worse. But still does not answer the question of whether the differential is due to sender inaccuracy, or engine degradation. But steady oil pressure albeit lower makes me lean more towards a sender issue.

I'd follow the least costly diagnosis procedure, whether it be a sender swap, sender replacement, DWAboat's wire swap, or mechanical test gauge and try and nail down the root cause.

 

[DWABoat]

Ok, so you have had the same differential between port and starboard for some period of time? If so that means at the least one engine has not recently gotten worse. But still does not answer the question of whether the differential is due to sender inaccuracy, or engine degradation. But steady oil pressure albeit lower makes me lean more towards a sender issue.

I'd follow the least costly diagnosis procedure, whether it be a sender swap, sender replacement, DWAboat's wire swap, or mechanical test gauge and try and nail down the root cause.

I was talking about doing the swap at the helm behind the gauges. If the instrument panel is like my 1989, the wiring is very easy to access and just swap all the wires from one gauge to the other. Can make little extensions using male spade connectors.

 

[Henry Boyd]

I was talking about doing the swap at the helm behind the gauges. If the instrument panel is like my 1989, the wiring is very easy to access and just swap all the wires from one gauge to the other. Can make little extensions using male spade connectors.

That won’t determine if the sender is bad, it will determine whether the gauge is bad. And that makes me realize jumping the wires at the engine won’t do it either.

 

[Woody]

I'd go this route, the only way to know for sure how much oil pressure you got. Harbor Frieght

 

[Yorkshirelad]

I'd go this route, the only way to know for sure how much oil pressure you got. Harbor Frieght
View attachment 93115

 

[Yorkshirelad]

Thanks Woody!