Weight of Oil

[jarrod1995]

Why does it require like 30 or 40, not 10/30 or 40. I'm asking due to the fact i had used 10-30 last time. Boat was running funny after a long run at 3000RPM. Checked my oil on a flat surface and was overfilled. So I was reading my manual and its calling for the one weight. 88 GM 5.0 Cobra outdrive.

 

[Don S]

Re: Weight of Oil

If over filled, the crankshaft hits the oil, which aerates the oil and causes the lifters to go soft, which affects how the engine runs when the valves don't open and close as they should.
Look over in the Non-Repair I/O and Inboards forum and the several hundred different oil threads. If your manual says use single weight oil and not 10w30 or 40, there is probably a reason, and it won't hurt a thing to follow what it says.

 

[Lou C]

Re: Weight of Oil

The reason why, is that multi vis oils will thin out at the sustained high rpm use that boat engines see. You don't run your car engine at a constant 3500 rpm usually (although come to think of it, I had an '89 Toyota Corolla GTS 1600 twin cam that ran 4100 rpm at 70 mph, and did it for 100K miles but that engine was built to rev). The conventional Chevy small blocks used in boats were not designed to run at sustained high rpms, hence the recommendation for single weight oil.

 

[jarrod1995]

Re: Weight of Oil

Don S and lou C, thanks for the info, The high RPM range running most of the time was the light bulb. I have also found my math problem on putting the oil in. When I read the bottle better she was 5+, so thats not going to happen again.