This is likely moot, as it sounds like the cap(s) failed, but was the
replaced blue cap and current cap tested? e.g. could you easily blow
air through it or did it make a honking sound when you did so?

My '88 also gushed coolant after a long hard drive then a bunch of
stop and go traffic on a hot day so this may be wishful thinking on my
part, but I often wonder if the valve in some brands of blue caps are
built so close to the upper end coolant temperature of a typical WBX
engine that if the engine is being driven in a manner causing it to
run hotter than normal, (and maybe its also connected to a marginal
cooling system) the valve in the cap fails due to the slightly higher
temperature.

I think this has been suggested here already but to test for a
combustion or exhaust leak into coolant path, with the cylinder at
TDC, could pressurized air be applied to each cylinder while watching
for air bubbles in the coolant? Tough to re create the fault though.
e.g. my engine coolant pressure tested fine while idling for at least
20 minutes.

Neil.

On 7/27/17, Eric Caron <ecaron1@comcast.net> wrote:
> Hi folks,
> So My 1.9 gas engine had a concern last year.  It seemed to be getting air
> in the coolant system and then not bleeding out.  I never identified the
> problem.  A friend gave me a original VW blue cap and my problem seemed to
> go away.

> Returning from a three hour pretty hard trip we noticed my van leaking
> coolant.  It was coming out the top of the overflow tank. I decided to
> continue the hour trip home as the temp was fine.
>
> No more coolant seemed to leak out.  Now that the van is cooled off the
> reservoir is full and the over flow tank is empty.
>
> Last year folks gave me some good suggestions as to what might be going on.
> As the blue cap seemed to solve my problem I chose to hope all was well.
>
> I think this cap is working correctly so my fear is that this means exhaust
> gas getting into my coolant.
>

--
Neil n

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