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Jim Grant's Tech Tips
93
VW Corrado V6, Mystery Coolant Loss
Q: My son owns a '93 VW
Corrado V6. In the span of 2-3 days of driving, the coolant in the reservoir
is completely empty. The dealer has checked the pressure, the container,
hoses, replaced the thermostat, checked head gasket possibilities, performed
carbon tests, almost everything imaginable, to no avail. They are at a
loss. They have not been able to duplicate the problem in the shop, even
under extreme conditions at high idle for an hour or so. It only occurs
during actual driving on the road. There are no visible leaks anywhere.
The only visible fluid is on the container itself, due to overflow when
driving. Help! Any suggestions? ....Nick
A: Idling
in shop for an hour or so, is not an extreme condition. It's rather easy
on the engine and cooling system. The real strain to a cooling system
is removing the heat that is created when the engine has to move the vehicle
at highway speed. A clue to your problem may lie in the answer to one
question. Why is coolant being pushed out of the container (coolant reservoir)
while driving? If the coolant is at the correct level and the cooling
system is functioning correctly, there is no reason for the coolant to
be forced out of the reservoir while driving. My suspicions are that the
engine is in the early stages of a failing head gasket. A failing head
gasket will cause coolant to be consumed by the engine, exiting as white
vapor via the tail pipe. The additional load of highway driving will force
combustion gases by the failing gasket into the cooling system, forcing
coolant out of the reservoir. (Which would explain the coolant overflow
problem.)
The
early stages of head gasket failure can be difficult to diagnose. Pressurizing
the cooling system overnight can be effective at identifying early head
gasket failures.
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