"Bob" wrote in message
m...
Interesting, but I am doubtful. I installed 2 new mercruiser 5.7 liter
I/Os in year 2000. The owners manual specified their own 25w-40 with
other multivis as alternatives. It specifically recommended against
synthetic oils. That seemed weird, so I called my friend who has a
1985 mercruiser 5.7 liter I/O. His owners manual was identical in all
respects about oil except it did not say anything about synthetic oil.
Somewhere between 1985 and 2000 Mercury saw fit to add one sentence to
the manual to recommend against synthetics. Neither manual listed
straight weight as a first or second option.

From my 1987 Mercruiser Blue Water Inboards Operation and Maintenance Manual
(260hp)

"IMPORTANT: The use of multi-viscosity oils specifically is not recommended
for use in MerCruiser Engines." Then follows a chart that recommends SAE
20, 30 or 40 depending on temperature. There is no mention of synthetics in
this manual.-Dano