"Mark Zak" wrote in
:

Can I use Mobil 1 5W-50 SuperSync oil (100% synthyhetic) in Mercruiser
GM V-8 350CID (5.7 L) in 15 year old marine engine?

Wow! At $3-5 a quart, the ol' GM 350 oughta damn near last
forever!....yeah, right.

The manual
specifies detergent 20W-40 or 20W-50 oils. What effect could have the
5W-50 viscosity range (5W vis 20W)?

Too thin when it's cold? 5 weight oil is like a sewing machine oil.
Wonder how well it keeps those cold rings away from those fragile, cheap GM
cylinder walls?? 20 weight is more than thin enough. We're being
conditioned so "they" can make $$$AU

The vessel is not used often, is
stored on hard stand, the winter temperatures are hardly below 10
degrees C and the engine is run at least once every month for about
10-15 minutes.

Hmm...I'd dump it if I didn't use it before it becomes worthless from the
awful boat depreciation. Oil pales in comparison to what its book value
drops.

I'm unfamiliar with Australian oil ratings as I'm on the other side of the
planet. Here, what concerns me is our oil (both dino and home made) has
been quietly devalued because it cannot pass the new SAE tests for 2-stroke
and 4-stroke diesels, once these were separated tests. So, you look on the
fancy can with the checkered flags and pictures of NASCAR race drivers and
in the SAE rating circle it says SJ or SK or whatever S rating the gas
engine manufacturers are using now....but NOT D-2 or D-4 for diesel use.
What have they left out? Diesel oils all have detergent in them because of
all the nasty carbon blowby that turns them black. Have they quietly
stopped adding detergent to keep the engines (gas and diesels) clean? Who
made that stupid decision....car manufacturers trying to wear out the cars?

I'm not fascinated with home made oils. I used Mobil 1 synthetic oil in my
Honda EU3000i electronic power plant a couple of times when it was new.
Synthetic oil was rated for air-cooled engines, not water cooled cars. It
was EXPENSIVE. I didn't care, it doesn't use much. When I sucked the
synthetic oil out and looked at it after 100 hours, I was scared I'd ruined
the Honda. It looked like it was BURNED!...it was BROWN! That ended that.
I started using the same Rotella-T (Shell) or Chevron's Velo 400 4-stroke-
rated DIESEL oils that American Truckers driving like hell down the
interstate with amazingly heavy loads on their engines run for millions of
miles between overhauls. What professional trucking companies use to
maximize their engine life speaks VOLUMES more as to what is the right oil
to use in any engine.....than the marketing department's motive of any oil
company trying to squeeze $5/quart out of some home made oil in the
checkered flag can. The genset seems ok at a thousand hours and Velo or
Rotella DON'T come out BROWN!...(c;