Mercruiser 4.3 low oil pressure at idle

[edwardsl]

I am the second owner. The first owner stored the boat most of the time. My oil pressure on start up is about 15-20 psi and at cruising speed is about 45 psi. After the engine is hot, and I go to idle, the oil pressure drops to 4-5 psi, and the alarm goes off. Increasing the rpms to 1000 brings the pressure back up to 10-15 and the alarm stops.

All pressures are measured by mechanical guage. The engine performance specs say minimum at idle is 4 psi, and I am at or just above minimum, but the alarm is disconcerting.

Per the computer, the engine has 126 hours on it, and NO CODES are recorded, despite the alrm having sounded many times. I had the engine checked my a Mercruiser service facility before purchase, with no problems reported (they did not see any low oil pressure, as the engine has to be run up to fully hot before it happens). What are your thoughts?

 

[Grub54891]

Re: Mercruiser 4.3 low oil pressure at idle

I'd hook up a separate test gadge to the motor and see if that one reads the same. If it reads better the sender is most likely at fault.
At least you will have a starting point for further diagnostics. It shouldn't be that low with that few hours.
Grub

 

[Don S]

Re: Mercruiser 4.3 low oil pressure at idle

What oil are you using? What is the idle rpm when the alarm sounds?

 

[edwardsl]

Re: Mercruiser 4.3 low oil pressure at idle

What oil are you using? What is the idle rpm when the alarm sounds?

I am using the Mercruiser recommended oil in weight 25-40. The idle rpm, per the mechanical guage, is just at about 600. The pressure will go up to about 10-12 psi at 900-1000 rpm.

 

[edwardsl]

Re: Mercruiser 4.3 low oil pressure at idle

I am using the Mercruiser recommended oil in weight 25-40. The idle rpm, per the mechanical guage, is just at about 600. The pressure will go up to about 10-12 psi at 900-1000 rpm.

As an addendum, I first replaced both the oil pressure sender and the alarm switch. Then I measured the oil pressure with two different mechanical guages, so the psi is accurate. Thanks for the help.

 

[Don S]

Re: Mercruiser 4.3 low oil pressure at idle

What year is your engine? What ignition system?
If you have a carbed engine, bump your idle rpm up to 650rpm (In gear, in the water. not on muff) and see if that's enough to stop the alarm. In neutral, you will probably see 675 to 700 rpm. NOTE: if you have Thunderbolt V, you have to be in base timing mode to adjust idle speed.

 

[edwardsl]

Re: Mercruiser 4.3 low oil pressure at idle

What year is your engine? What ignition system?
If you have a carbed engine, bump your idle rpm up to 650rpm (In gear, in the water. not on muff) and see if that's enough to stop the alarm. In neutral, you will probably see 675 to 700 rpm. NOTE: if you have Thunderbolt V, you have to be in base timing mode to adjust idle speed.

it is a 2000 4.3 EFI, so not carbed. she was very lightly used by te original owner (125 hours on the computer when check, and no faults noted either..). the alarm does go off if I bring the rpm up to 8-900.