Re: [OMC-Boats] What type of oil for 1967 Sportsman 120

On Mon, 10 Aug 2009, Kenneth Gullicksen wrote:

> Just curious, why 10W-30? I have always used straight 30 in my boats,
> but I use them in a fairly modest range of (outside) temperatures.

I started using straight 30W originally, but eventually decided there was
no reason to avoid the improved performance of modern multiweight oils.
Straight 30 acts like 30W when it's warm, and acts like warm 50W (or worse)
when it's cold.

Why not use an oil like 10W30 that acts like 30W when it's warm, but acts
like cold 10W (which is probably similar to warm 30W) when it's cold? It
flows better on start-up, so everything is being lubricated more quickly.

Unless there's some bizarre reason the engine can't tolerate a lower
effective oil thinness cold than it can hot (maybe some unusual varying
clearances?), it shouldn't hurt anything... The only situation where I
stick with straight oils anymore is in applications when a non-detergent is
required.

I think we'll see a lot of improvements in engine design and reliability
over the next ten years, as some of the higher-performance synthetics
become accepted in the US. They're already common in Europe - we use 0W40
in some research engines and I've seen 0W50 as well. Those oils are
amazing - they pour the same at freezing as they do at temperature - but
also cost $10-20/quart.

However, since boats are rarely used in extremely cold temperatures, are
typically used for far less hours than engines in cars, and probably have
<1/10 the number of cold-start cycles, the cold temperature performance is
fairly irrelevant. I find it's often cheaper to buy 10W30 than 30W though,
as the straight 30W never goes on sale.

Ethan

-- 
<a href="http://www.engr.wisc.edu/~brodskye/"> Ethan Brodsky </a>