I wouldn't second guess the advice of the maufacturer. And unless
there is evidence, I wouldn't assume or jump to the conclusion that
price of the oil has anything to do with it.
For example, for my boat, Mercruiser lists straight 40W for their V8
marine engines, with no off the shelf multi-grade recommended. Now
it's hard for me to believe they are doing that based on oil cost,
since in marine applications, the cost of oil is trivial.
And it's not true that mulit-grade is not used in lawn mowers. My
Honda takes 10-30.
I would use the recommended oil and make sure it's changed at least the
recommended hours or once a season.
You might consider synthetics as being a single grade oil. And
synthetics are much better at standing the high temperatures you find in
air cooled engines. It just happens that it does not get as thick as
conventional oils when it gets cold and will meet the 5W30 specification
without additives. In order to get conventional 30 weight oil to thin
out when cold it is necessary to add viscosity improvers. The VI has
been a disaster in some of the hot running car engines. Note that some
now will not warranty an engine if you use 10W40 conventional oil. I
saw one engine where the rings were froze into the pistons due to the
VI. It was necessary to throw the pistons away.
The first number "5" means at 32F the oil has the same viscosity as
straight weight 5 at 32F. The 30 means that at 212F it has the same
viscosity as straight weight 30 at 212F. So when cold it is still
thicker than it is when it gets hot.
Good Post but you have it backwards
They start with the low no. base oil
5W then add Polymers which prevent the oil from thinning as much as it
10W-40 and 5W-30 require a lot of polymers
polymers can shear and burn forming deposits and frozen rings as you say
among other things
The wide range oils are more prone to viscosity and thermal breakdown due to
the high polymer content
And leave you with the base oil You wouldn't put single grade 5w in would
So when it breaks down you have 5W base not 30W
10W-40 IS Well know to do this and As you said Very few manufacturers
recommend 10W-40 any more
and some threaten to void warranties if it is used
So the other post that said 10W-40 is probably better is flat wrong
20W-50 is the same 30 point spread But has less polymers
the polymers used for multi grade are elongated and kind of curl up as
they get cold.
When Mobil 1 first came out I was having oil problems when pulling a
trailer over high mountain passes. Even with 20W50, I would be down
almost a pint or more after going over a high pass. When I would open
the filler cap fumes would come out. I decided to give the Mobil 1
(only came in 5W20 at that time) a try. Much to my amazement my oil
usage essentially disappeared. My theory is that engine was running so
hot it was vaporizing the oil.
I read where it takes about twice as much polymers to make 10W40 as it
does 10W30. It caused a lot of stuck rings in hot running engines.
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