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SF writes:
They want you to shut off the engine with the shutoff switch, not the fuel
petcock.
They don't want you to fuel starve the engine.
Pre 196x outboards (pre TCW 2 or was it 1?) used automotive oil mixed with
fuel... In those it was recommended to run engine dry of fuel before storage.
Later it was discovered that doing so caused motor innards to rust and engines
to wear out sooner. Somewhere along the way OMC started recommending that
outboards NOT be run dry of fuel as this would cause corrosion and undue
wear...
All OMC and MERC outboards require that you shut them off by a button. This
button disconnects power to spark plug. So motor runs on without spark and
lubricates with unburned fuel.... Preventing formation of rust... After you
shut if off they recommend you shut the fuel supply off (NOT BEFORE) to preven
gas spilling out of the motor...
It is recognized that fuel dries up in fuel lines and carburator, if engine is
stored for more than 60 days or so... In those cases, there is a fuel additive
(Sta Bil at K or W mart) that prevents gasoline from going bad or evaporating.
OMC & Merc recommend that this stuff be added to fuel, if engine is not going
to be used for more than 60 days or so... (Check the long term storage
instructions chapter in your manual)
Under no circumstances should you follow advice to run engine dry to prevent
formation of gum/varnish in fuel and carb. Use a fuel stabilizer!
Many of these people recommending you run outboard dry are basing this on old,
old info from old outboards. (Sea Gull [uses 1940 technology] still does
this). Yes, even some old mechanics still recommend this method. Bad habits
are hard to correct.... These individuals have not read their owner's manuals.
Read you owner's manual and follow its directions... Your manufacturer has an
interest in your outboard performing adequately for as long as you own it...
They want you to buy their brand next time...
Best
SF
BTW: They also recommend you store engine with powerhead higher than propeller
to prevent water from dripping from exhaust (usually submerged) into
combustion chamber...
I purchased manufacturer service manuals and parts manuals for my three
outboard motors (130, 8, 3.3). Yep, I do read those manuals...
With all due respect, I need to point out that the manual for my Mercury
outboard (a 1987 2.2 horsepower) states quite clearly that the motor should
be run at idle speed with the petcock in the "off" position and the cap
vent closed until the motor stops before the motor is removed from the boat
or stored for an "extended" period.
Making remarks like "Under no circumstances....." may be a bit presumptious
when it appears that manufacturers offer differing advice on how to operate
their products. In addition, as it is likely that a small outboard will be
unintentionally run out of gas a number of times during it's service life,
I suspect that the engineers have designed it to tolerate that.
I would like to plead with the individual who said they leave the fuel
petcock continually open not to do so. In addition to creating a safety
hazard for themselves, they are also releasing un-necessary volumes of
completely unburned hydrocarbons into the atmosphere. One of the most
effective pollution control devices on an automobile is that which contains
the evaporation of raw fuel from the tank and fuel delivery system.
If the motor manufacturer advises against intentionally running the engine
dry (as OMC apparently does) perhaps using one of the aforementioned
additives will allow you to store the motor with the petcock and vent
closed.
Dave Kautz
P-15 #1632