Bruce,
You are a nice guy, but you are not correct here. Please pay close
attention, heavy lube oil contamination will create detonation in spark
ignition engines. It will melt pistons, spark plugs and heads, especially in
outboard motors. The percentage of oil in the fuel that creates this damage
is a matter of heat.The higher the heat of the combustion chamber, the lower
the oil percentage threshold that diesels the fuel mix . The reason this is
more dangerous in outboards is because the noise of detonation is muffled by
the water jacket and masked by excess ambient noise in the boat.
Additionally the severity of this condition is greatly amplified by throttle
position and the general mode of operation is WOT. If you think for one
second that flash point of fuel is not significant, place a drop of gasoline
down the barrel of a daisy BB gun and fire it. No change. Place of drop of
oil in the barrel and repeat the test. It easily detonates when the spring
is released. I used to this all the time as a kid.
Steve

"Bruce In Bangkok" wrote in message
...
On Sun, 14 Jun 2009 13:03:58 -0500, Brian Whatcott
wrote:

Not so sure. Gasoline flashes fairly low. But oil has lower octane than
any gas. So pinking or detonation could still be an issue, no doubt.
That's if the compression still makes it up there.....

Brian W

Steve Lusardi wrote:
50 to 1 Remember, too much oil will reduce the flash point of the fuel
and
create detonation, which will melt piston and head.
Steve

"rckchp" wrote in message
...
OT. I'm reactivating a 1997 Evinrude 9.9 hp outboard and I've
misplaced the owner manual, and I don't remember the proper oil mix
ratio. Is it 50 to 1, or 100 to 1? Thanks.

Flash point has nothing to do with detonation which is controlled by
octane rating and compression.

Flash point is the temperature at which vapors ignite and since
kerosene (with its higher flash point) will burn in most internal
combustion engines it seems that flash point is of only minor
interest.

Cheers,

Bruce
(bruceinbangkokatgmaildotcom)