Bob wrote:
John Wentworth wrote in message ...

WaIIy wrote:

Mercury recommends 25W-40 oil for Mercruiser engines, back in '89 they
rcommended straight 30 weight. In '89 Mercury sold 30 weight and warned
against multi-viscosity oils, now they recommend and sell it.


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.


In a Mercury Marine service manual I have that covers the early '80's
the recommendation is:
Lowest temp is 90°= SAE 40 "SE"
Lowest temp is 32°= SAE 30 "SE"
Lowest temp is 0°= SAE 20W "SE"

For much of the United States that equals SAE 30, oil to be changed
every 100 hours or 60 days, whichever comes first.

Also: " We recommend Mercury Marine 4-Cycle Marine Motor Oil Formula 4R.
If not available, use any good grade automotive oil of correct viscosity
which has an API classification of "SE".


One thing for sure, the topic "Oil for my boat" will produce a deluge of
responses. Can a "dead reckoning" topic be far away?