Re: [DML] 5w30?

[William T Wilson <fluffy@xxxx>]

( Moderators note: This subject can be debated endlessly and enough has been said now and in the archives. Unless something entirely new comes up I'm killing the thread. )


On Wed, 28 May 2003, thomaspaulmccoy wrote:

> What are the disadvantages of using 5-30?

Similar to the disadvantages of 10W40. Oil with a very wide viscosity
range has more chemicals in it and depends on them more. As a result it
is more prone to breaking down and suffers more as it gets contaminated, 
and the lubrication qualities are less at the temperature extremes. A 
5W30 oil is really 5-weight oil with thickeners in it to make it act like 
30-weight oil when hot.

Most engines spend most of their running time hot, so the net effect of a
wide viscosity range is that your oil is basically just not as good during 
normal to hot conditions.

Depending on your climate 10W30 (cold), 15W40 (moderate to hot) or 20W50
(very hot, like Florida or Texas in the summer) are good oil viscosities
to use.

Note that this does not apply to synthetic oils. Synthetic oils can have
wider viscosity ranges without any of the problem of ordinary oil. If you
are using fully synthetic oil (which very well may be what GM is using in
your new car) 5W30 is better than normal 10W30. But stay away from plain 
5W30.

> was looking to boost DMC performance, wouldn't 5-30 be a decent
> solution?

Oil thickness doesn't have that much of an impact on performance. It can 
improve your fuel economy, though - that's probably why GM is specifying 
the thinner oil (even if it isn't as good for the engine long-term).