K. Smith wrote:


Use the 40, if that's the recommendation.

The multigrade oils only thicken up when they get really hot
(various additives, plastics etc expand & change as the temp rises, but
the base oil is the lower claim, so a 20-40 is actually 20 grade oil
with additives to help when it gets hot), as in a properly thermostatted
car engine.

The trouble or one of the troubles:-) with raw water cooled engines
is they can't run the normal high (near boiling temp) thermostats, so
the engine & therefore oil might not get really hot & if it were
multigrade it "might" not thicken enough to give the engine proper
protection when worked hard.

Other end of the scale; some boat engines, skiing or heavy cruisers
can really put the engine to work & although the raw water low temp
thermo cools the block, still & all the oil can get hot, again 40 is
better than 30 in that case too.

K

I am sorry, but whoever "penned" the above obviously knows nothing about
lubricating oils & films.

K. Smith...: please post back and tell us this was some kind of joke or
flame...

Multigrade oils do not "thicken up" when they get hot, hotter, or really
hot. You can demonstrate this in your kitchen today with a quart of
your favorite 10W-40 and a candy thermometer.

As to the OP, straight 40 weight oil would be fine, espescially with the
older engines with seasonal use on Lake Erie, but for the high costs
involved with the ownership, maintenance, & possible replacement of
marine power, I recommend, and follow, that you use a multigrade Mobil 1
product for maximum protection - and Purolator Pure 1 filters.


Rob