What happens when an engine is overfilled
with oil?
So you topped up the engine when it was warm
after getting a faulty dipstick reading, or you
put too much oil in when you changed it
yourself. What's the worst that could happen?
Well the problem with this is that the next time
the engine is run, the windage in the crankcase
and other pressures generated by the oil pump,
etc. place a great strain on the seal on the rear
main bearing.
Eventually, often much sooner than the
ordinary man in the street might expect, the
rear main bearing seal ruptures, and the engine
becomes a 'leaker'. If you've got a manual
gearbox, this means one thing: this oil goes
right onto the flywheel and the face of the
clutch disc. A lubricated clutch is A Bad Thing. If
this still goes unnoticed, the front seal is the
next to go, and the engine then becomes a
'gusher' (or to be more colourful, it starts
pissing oil all over the place ). As well as
smothering the clutch with oil from the rear, the
oil now coming from the front leak will be
neatly distributed about the engine bay as it hits
the front pulley - often propelling it out as far as
the brake discs. At the same time as this
Hollywood disaster movie is unfolding outside
the engine, things aren't working out any better
on the inside. As you can see from the diagram,
the correct oil level is really close to the rotating
crank. Overfilling will mean the crank dips into
the oil and churns it into a froth. Froth is good
on certain types of coffee but not good in an
engine. The mixture of aerated oil will be forced
into the bearings and in case you didn't know,
air is not a lubricant. Typically this means that
bearing damage will follow quite rapidly,
especially if you are driving on a motorway.
You'll know bearing damage when you get it.
The engine smells like a garage mechanic
cooking over an open flame and the noise
coming from the engine is the sort of thing
you'd normally hear in vaudeville plays when a
piano is pushed down a flight of stairs. As if
that all wasn't bad enough, the excess oil gets
thrown up into the piston bores where the
piston rings have a hard time coping with the
excess oil and pressure. It gets into the
combustion chamber and some of it will get out
into the exhaust system unburned resulting in a
nice patina of oil all over the platinum surfaces
of your catalytic converter. This renders it
utterly useless for good.
Oil and Engines 4
