"Charles T. Low" wrote in message ...
I might have missed some messages in this thread, but has anyone suggested
reading the owner's manual?

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Charles T. Low
- remove "UN"
www.boatdocking.com/BDPhoto.html - Photo Contest
www.boatdocking.com
www.ctlow.ca/Trojan26 - my boat

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"Woodchuck" wrote in message
...
I think the Merc oil is 25w40 and really isn't much more than the price of
regular oil. I would go with what the marina said unless you do a lot of
hard running or live where it's HOT! The use 40

"Jodon2" wrote in message
...
Just had a new MERC factory rebuilt engine put in 2 months ago and now
it's
time to change the oil in it. Marina that put engine in put in straight
30
weight oil and he said to stick with this grade. Is this ok? Thanks.
Joe


More than you wanted to know about motor oil:
http://www.fourfold.org/RoverWeb/OilFAQ.html

If you don't have the patience to read then the Merc oil 25w40 is one of the better oils for your boat.

Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely. Always use a multi grade with the narrowest span of viscosity that is appropriate for the temperatures you are going to encounter. In the winter base your decision on the lowest temperature you will encounter, in the summer, the highest temperature you expect. The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best.


Very few manufactures recommend 10W-40 any more, and some threaten to void warranties if it is used. It was not included in this article for that reason. 20W-50 is the same 30 point spread, but because it starts with a heavier base it requires less viscosity index improvers (polymers) to do the job. AMSOIL can formulate their 10W-30 and 15W-40 with no viscosity index improvers but uses some in the 10W-40 and 5W-30. Mobil 1 uses no viscosity improvers in their 5W-30, and I assume the new 10W-30. Follow your manufacturer's recommendations as to which weights are appropriate for your vehicle.