03-47
SECTION 03 - ENGINE PREPARATION
FUNCTION OF THE COOLING
SYSTEM
All Sea-Doo watercraft are equipped with a total
loss cooling system. The water supply is taken
from a pressurized area in the jet pump between
the impeller and venturi. The water passes
through a tee, where a small amount is diverted
into the exhaust stream (refer to WATER INJECT-
ED EXHAUST SYSTEM in this section), and the
majority continues into the exhaust system cool-
ing jacket to be warmed before entering the en-
gine. On the 1988-91 engines, water enters at the
bottom of the exhaust manifold and tuned pipe
cooling jackets; then to the engine. On the 1992-
97 engines (excluding the 717 and 787 engines),
the water enters the cooling jacket on the tuned
pipe, and travels into the cooling jacket around the
exhaust manifold, after which it enters the cooling
jackets of the cylinders through small passages
under the exhaust ports.
The flow of water through the exhaust system
has changed slightly from the 1988-91 yellow en-
gines to the 1992-97 white engines; however, the
most important point is that on either type of en-
gine, the water is still pre-heated by the exhaust
system before entering the engine cooling jack-
ets.
On the 717 and 787 engines the water first enters
the cylinder head, unlike previous models. The
cylinder head cooling jacket has been divided into
2 sections. One side of the head’s water jacket
(exhaust side) has cool incoming water circulate
around the combustion chambers, then into the
tuned pipe and exhaust manifold cooling jacket.
The preheated water then enters the cooling jack-
ets of the cylinders. From the cylinders the water
flows upward through calculated holes to the out-
let side of the cylinder head. The outlet side of the
cylinder head’s cooling jacket also houses the en-
gine temperature sensor, where the now hot wa-
ter escapes through the engine water outlet hose.
Some aftermarket companies may suggest that
the cooling system be re-routed to feed cold wa-
ter directly to the engine instead of allowing the
exhaust system to warm it first. This change
should be approached with caution as random
changes without adequate testing and develop-
ment could be detrimental to the engine. Chang-
ing the routing of the cooling system could result
in less power output and engine reliability.
On the 1988-91 engines, the cooling water pro-
ceeds into the engine via a water distributor into
the crankcase, then up to the cylinders. On the
1992-97 engines, the cooling water proceeds
from the exhaust manifold cooling jacket into the
cylinder cooling jacket via the passages below the
exhaust ports. On all engines, the water sur-
rounds the cylinders and moves upward through
calculated holes in the cylinder head exiting the
engine at the intake side of the cylinder head.
Summary of Contents for Bombardier
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