Subject: 40W oil causing wear problems over 30w?
From: Kevin Stevens

(LaBomba182) wrote:

The capt. and eng. disagree. They start saying that running a heavier
weight
oil could cause wear problems and make the engine work harder over time.
And
as an example they compare it to what can happen if you use a heavy weight
oil
in a high revving street/race car.

Like what? Frequently race cars *do* use heavy weight engine oils
because of the high temperatures involved. You use the lightest you can
get away with because you want to reduce parasitic power loss, but
that's not for engine durability - keeping the engine in one piece is
why you have to use heavier oil in the first place. As for "work harder
over time", I don't know what the "over time" part is about, but yes,
there is higher parasitic power loss with greater viscosity. But again,
this isn't a race engine where you're concerned with peak power output
anyway. Where you'd see it show up, if noticeable at all, is gal/hr.

The Northern Lights Tech I spoke with about this on the phone said he could see
no real down side except for perhaps an increase in oil consuption. But due to
the fact that 40W is not mentioned in the specs manual it could be a warrenty
issue.



In the end we will end up putting 15-40W oil in the tank for the engines
and
gensets (as per specs) and keeping some 40W in bottles for the trannys.

Something you *do* want to stay away from are the wide-range
multi-viscosity ratings. They are obtained with the use of modifiers
that a) break down the most quickly of any of the oil components, and b)
displace the oil itself in the lubrication
mix.

I'm not a big fan of multi wieghts either. But they are speced for the mains
and gensets.


But other than the warranty concerns, I'm I missing something here?
Would using 40W over 30W in the gensets with of course changing it at the
proper number of hours and making sure that the ambient temps never get low
really cause any long term problems?

I'm reluctant to guess without knowing the manufacturer's reasons for
specing a particular viscosity.

In the manuals the oil recommendations are based on ambient air temps.

*Generally*, unless you're doing
something silly like running 135wt gear oil in something that calls for
30wt, or oil used in hydraulic systems, the tradeoff is simply parasitic
loss vs adequate viscosity at high temp. Most damage is caused by oil
that is a) chemically incorrect for the application (GL-4 vs GL-5,
antagonistic modifier packages, etc.), b) underfilled, overfilled, or
never changed, c) inadequate viscosity at high temps.

That's the way I have always understood it.

Capt. Bill