Odd cooling problem

[amalventano at sc.rr.com (Allyn)]

> No coolant leaks while driving But when I stop
> the car and shut it off a few seconds later coolant spill all over the
place.

check the coolant cap. it may have a dry sealing surface (its supposed to be
soft rubber). as for the pressure increase, all cars do it. when the engine
is shut off, coolant stops flowing. residual heat from the hotter parts of
the cylinder head/block transfers into the coolant, causing that coolant to
heat up and expand (steam forms if there was enough residual heat).

note: the 'high' mark on the reservoir is intentional. it allows air to act
as a bubble against the expanding coolant. if you overfill the reservoir,
there wont be enough air bubble, and the pressure will rise above 15 psi,
causing the relief valve to lift (which is part of the coolant cap). this
can appear to be a leaking cap, as the coolant exits from the same place.

hth
AL