I have run straight 30wt Castrol in my 5.0 Merc for 15 years. Reason:
the oil temp guage I installed in my '70 F250 390 engine always reads
320°-340° just tooling around town at low rpm. Imagine what the oil temp
is in your 350 at 80% WOT. This is much higher oil temp than cars
usually run. This can break down multi grade oils. Straight grade oils
are resistant to high temp breakdown better than multi grade.
JR
I'm not an oil engineer, I just play one on TV

Captain Chaos wrote:

Just finished my first weekend of boating. Woo hoo. Lots of fun.
Maneuvering around the marina is a lot harder than it looks though. I
don't think the brakes on my boat work.

I need to change the oil in both the motor and outdrive. The previous
owner said he used synthetic. I've always run conventional oil in all
my machines, mostly cars and motorcycles with the practice of changing
the oil frequently. This practice has never failed. With the cost of
synthetic, I'd rather stick with conventional.

The motor is a 350. I was planning on using 10-40. Any problems with
this? Any other recommendations?

OMC Cobra outdrive. I have no idea what oil to use in this or how
much?

Any problems either with the motor or outdrive going from synthetic
back to conventional?

The only problem I've experienced with the boat is that shifting
between foward, neutral, and reverse is a little bit harsh. I'm not
sure if that is normal since I've never driven any other boat before
and have nothing to compare it too. It goes into gear okay, but you
have to use a fair amount of force to do so. Boat is an '89 Dynasty
runabout.


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Home Page: http://www.seanet.com/~jasonrnorth