Mercruiser 4.3 low oil pressure.

[mastercylinder63]

I took my boat out on a shakedown cruise. The Starboard engine is a 2009 4.3 carb motor. It always read a constant 40psi, but today was different. After an hour of use, the alarm went on and oil pressure dropped near zero. I shut the motor down for 15 minutes and then restarted it. I got 25psi @ 750rpm idle. When I hit 1100rpm the pressure goes back up to 40psi. I don't rev the motors more then 4500rpm. The oil is fresh 5-30w. I'm going to check it tomorrow and start the cold engine. I guess if it reads 40psi it may be the oil weight or brand, I'm not too sure. Every year I use Castrol, but this year I used Mobile, but the port engine is a solid 40psi at all rpm's. Any suggestions???

 

[Don S]

Re: Mercruiser 4.3 low oil pressure.

That's normal. Warm engines always have a little lower oil pressure. And it's normal for the pressure to drop at idle compared to cruising rpm.

 

[Another retired guy]

Re: Mercruiser 4.3 low oil pressure.

The port engine must be in good shape to maintain steady pressure at all rpm's
If the starboard engine keeps dropping to "near zero" at idle, I would go to a slightly higher viscocity oil.

 

[mastercylinder63]

Re: Mercruiser 4.3 low oil pressure.

yeah. I would say it's normal if it always did this, but since 2009 this engine was always at 40psi. The port engine is original 1997 engine and it's always 40psi as well. I think I'll go back to the Castrol and see if there's a difference.

 

[mastercylinder63]

Re: Mercruiser 4.3 low oil pressure.

Interesting, this morning my older port engine started to drop to 25psi @ idle as well. So today I went back to Castrol 10w 40 in both engines. Idle is back up to 40psi just like it was before. Didn't think viscosity made much of a difference in the GM V6 engines, but in my engines it clearly does.

 

[Another retired guy]

Re: Mercruiser 4.3 low oil pressure.

Viscosity will always make a difference in a hot engine. I remember the days when my car needed 20 50 oil in order to maintain 10psi at hot idle !