Generally speaking, the power-to-weight ratio of a liquid-cooled sled
will be much better than a fan-cooled sled (you have to consider the power
versus the total weight of the sled and rider(s) to make a valid
comparison). Even though the cooling system adds significant weight to the
sled, it's relatively small compared to the total weight of the sled, rider
and fuel load. So, a liquid-cooled sled will normally be quicker and faster
than a fan-cooled sled of the same displacement.
Any perceived reliability advantages for the fan-cooled sled stem mostly
from the fact that they are making less power for a given displacement than
the liquid-cooled sled. When you start cranking the horsepower up, they
become less reliable and more finicky than the liquid-cooled ones.
Fan-cooled snowmobiles are generally more tolerant of over-heating than
liquid-cooled ones; but that's really just due to the difference in the type
of head gaskets and/or o-rings that they both require. The fan-cooled
engine has a more robust, less fragile gasket system... because it doesn't
need holes in it to let coolant flow in and out of the cylinder head. It
also doesn't have to seal against pressurized coolant which means it can be
made from more heat resistant materials.
The liquid-cooled engine, on the other hand, depends on the coolant to
prevent the head gasket or o-rings from overheating and burning up. When
the liquid-cooled sled gets too hot, the steam accumulates at the top of the
engine... leaving the gaskets to fend for themselves against the heat.
Again, the liquid-cooled engine is generally making more power... which
generates more heat, too.
Either engine type will sustain severe damage if the cylinder walls get
hot enough to break down the oil film that protects the piston from the
cylinder (and vice versa)... so neither engine is immune to overheating
damage.
With mild overheating, the cylinder on the fan-cooled engine will expand
more... which increases the clearance between the piston and the cylinder,
and makes more room for oil. However, if the clearance gets too large...
the rings will be unable to seal and will let hot gases blast past them
(ruining the rings and burning the oil off of the cylinder and piston).
Fortunately, that's accompanied by a fairly large reduction in power... and
most people are smart enough to stop then.
The liquid-cooled cylinder will still have coolant around it and will
remain very close to it's normal size... so it will usually keep making good
solid power even when beginning to overheat; right up to the point where the
head gasket fails and the anti-freeze strips the oil film off of the piston
and cylinder. Then it usually stops quite suddenly!
The one possible achille's heel of the fan-cooled sled is that it is
possible to over-cool them on a very cold day. What happens is that the
cylinder will get cold enough to actually shrink the clearance down (around
the piston) and seize. The piston will grow to roughly the same dimensions
if the jetting is in the ballpark, but the cold cylinder will not... so it
gets tight.
Usually what happens is that when you get on the throttle and start
heating the piston significantly... you're also spinning the fan very fast
and ramming a lot of very cold air in through the hood vents because you're
going fast; so the piston is growing and the cylinder is shrinking! >;-(
But hey, all that's just based on my own experiences... your experience
may vary! >;-}
David
Post by Newbie SledderI have an 02 GT Fan (500).
Pros: I can run it all day in the warmer weather whereas the liquids need
to cool off in the snow. The fans 'might' be more maintenance friendly too
cuz you don't have to deal with coolant.
Liquids tend to be quicker or faster off the line though.....from what I've
heard.....although I'm not sure if it's true or not.
Good luck......
I am tossing around if I should go the 2004 ski doo legend GT 500 liquid
or
GT550 fan cooled. And what are some pro's and cons of the two types.
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