Re: 2001 225 4-stroke smoking
I'm not Rodbolt, but I could play him on a TV series, plus I once stayed in a Holiday Inn Express!
The following are excerps from the 2003 Yamaha Marine Technical Guide starting on page 2-5
OIL CONSUMPTION
The 4-stroke outboard design and duty cycles vary from a typical 4-stroke motor. Keeping these differences
in mind it is common to see oil consumption. There is no specification for how much oil consumption is
acceptable. The pistons run in a horizontal cylinder. The piston rings do not have location pins like a 2-stroke
engine. The piston rings can rotate, allowing the end gaps to align on the lower side of the piston. This would
allow more oil to be consumed at any given time. This is normal. There is nothing wrong with the engine. The
duty cycle of the engine is another aspect to keep in mind. The outboard engine runs at a higher rpm range
than a typical 4-stroke engine. It is not uncommon to have a set of twin engines where one burns more oil
than the other one.
Oil on the backside of the piston may lift the piston by simple hydraulics and this lifting action will allow oil to
get past the rings. The higher the duty cycle the more common this hydraulic action may be. There are a
number of mid-range, 4-stroke engines that are mounted on marginal boats. These boats are on the verge
of being under powered just because the customer wanted a 4-stroke but was limited in choice. The customer
expectations of engine performance are far more than what it can deliver in a marginal application.
SMOKING at STARTUP page 2-8
When storing 4-stroke models (either overnight or for any length of time), they must be trimmed to a positive
trim angle. As you know, the 4-stoke engine has an oil pan in which the oil is circulated through the engine
to lubricate. While the engine is running, any oil that is on the backside of the piston will be pushed towards
the front of the engine. The oil ring performs this pushing action. When this oil is pushed, it will then fall back
into the oil pan to be re-circulated again. When the engine is turned off, the piston motion stops. Therefore,
any oil left on the backside of the piston will run to the bottom of the cylinder sleeve. If the engine is stored
in an even or negative trim, the oil will puddle against the piston and rings. In time, this oil will seep past the
rings and into the cylinders, thus causing the engine to smoke on initial start up. This is normal when the oil
puddles. The only way to stop this from happening is to trim the engine to a positive trim angle and allow the
oil puddle to run towards the front of the engine where it will drain into the oil pan.
