I'm going through something similar.

In my case, during longer harder trips, especially on hot days, I'll
eventually start hearing gurgling noise, see bubbles floating back into
expansion tank via top connection at tank, fill tank may overflow. Level
certainly increases at fill tank.

With helpful list input in mind, I'm pretty sure excess pressure in coolong
system due t a compression leak at engine, is damaging the
valve in blue cap to the point of failing open. But. It doesn't tend to
happen on shorter trips in town.

I.e. if hoses and other parts are in good shape, the blue cap is taking the
hit.
90% of my cooling system has been rebuilt.
One thing I haven't done in a while is measure temps at heads, big metal
pipe off engine.
My guess is my engine is running hotter than it should at times.

Just my .02.

On cap #3....   ;)

Neil.

On Wednesday, July 20, 2016, Eric Caron <ecaron1@comcast.net> wrote:

....
>         With the known working cap my system seems to be operating
> perfectly again.  the expansion tank fills back up after a long trip and
> the over flow tank goes down when the appropriately.
>
>         Can my engine heads actually be ok and the other behavior be due
> more to the cap?  Or, is the cap working well masking the introduction of
> the exhaust gasses and now I just don’t know they are there?
>
>

-- 
Neil n

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