Coolant overflows GTV6

[C M Smith <cmsmith@domain.elided>]

To Richard

Does the GTV6 use the pressurized expansion tank or regular rad cap and 
expansion bottle? If regular rad cap then your symptoms are of a failed rad 
cap pressure seal. The seal is effected by a spring pre loaded to the 
desired static cold pressure above atmospheric. If pressure exceeds that 
(as it does routinely) a small amount of coolant is ejected into the 
expansion or overflow bottle. As the system cools down a vacuum develops 
opening another seal drawing coolant back into the system. This latter 
valve appears to be working fine on your car.

The rad cap could be sticking open, i e once the pressure pushes the seal 
open the spring is too tired or the rubber too fossilized to re seal the 
now hot coolant. Result is too much overflow from a cooling system trying 
to operate at atmospheric pressure.

I had the expansion valve fail fully stuck closed on my 98 Japanese car 
(which still uses the now obsolete rad cap system) which allowed the 
coolant to blow out the weakest sealing point (the rubber seal around the 
engine block heater inserted into a 'freeze" plug hole) which resulted in 
coolant being drawn back in from the expansion bottle without returning any 
when hot.

good luck


Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner

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