la bomba, you have smashed what little reputation you had left with your
question. Yet, you seem genuinely interested in the answer.

Two problems exist with using a heavier than spec'd oil. first, and the
biggest problem, is pushing that cold, thick oil around upon engine startup.
It can take many seconds for pressure oil to get to the all the bearings
needing pressure oil. The thicker the oil, the more seconds it takes.
Multi-weight oil was in fact expressly developed to reduce dry engine
startup's, particularly in colder weather. Original multi-weigh oils were no
over the long term as viscous as the oil they replaced, but the dry start
problem was cured. Today, most engine manufacturers recommended multi oils.
If you use a straight weight oil ***be sure*** to properly prelube the engine
before startup. Even with milti oils this ai good idea, with straight weights
it is really important.

Second, straight weight oils that are tood supposedly can push out seals. So I
have heard for decades but I never saw an engine that seemed to have lost its
seals due to anything but long use. Maybe it happens, dunno.

Kinda third, heavier oils take more hp from the engine to keep itself running.


OK, so I'm sitting around with the captain and his engineer friend on the new
boat I'm project managing/co-captaining and we are trying to work out how to
run the same weight oil in the engines, gensets and trannys so we only have
to
fill the clean oil tank with one weight oil and not carry any extra buckets
of
different weight oils with us.
The CAT engines and ZF trannys can use 40W oil as per their specs but the
Northern Lights gensets only recommend up to 30W oil. The CATs could run 30W
but only at 86 deg. ambient air temps. We will certainly be seeing higher
temps
than that.
I tell the capt. and eng. that based on the ambient air temps we will be
seeing
even with the Delta-T fans that if it weren't for a warranty issue I wouldn't
hesitate to use 40W oil in the gensets.
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. I point out that this is a diesel not a high
revving street/race engine. They back off that point a bit but we still go
round and round in a civil fashion.
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.

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?



Capt. Bill