On Jul 24, 7:51 pm, "jetta107" > wrote:
> I have a '97 jetta TD, and I thought I was overheating only at high speeds,
> but it seams to be loosing coolant threw the vent on the resevoir? (
> presure in cooling system?). Then it begins to overheat.....Since there is
> no rad cap, does the resevoir cap regulate the presure?

Boiling coolant. A wrong mixure of coolant to H2O or exhaust gasses
getting into the water jacket are first thoughts. Over pressurization
is common if you have either of the afore-mentioned conditions. If
you find a new cap and the same thing happens, you have to look at the
above. Overheating is the key. Why is this happening??? If there is
a leak (cannot create a constant pressure) in the cooling system,
overheating will occur. If you have the wrong mixture in the system,
this will occur. If exhaust gasses are escaping into the cooling
system, this will happen (such as with a blown head gasket). If
timing is off, this also may occur (although this is probably more of
a long-shot). Make sure w-pump and thermostat work correctly. From
there, check for leaks and/or losses of pressurization. I have a 16v
and have to constantly monitor these things, and I know how far-
reaching these problems may be. Good luck...........