> Last night, after driving around with cylinder compression leaking into my
> cooling system creating excessive pressure, I had a major head gasket
> failure that was blowing coolant out like a firehose.  Being very pi##ed
off
> that my van is falling apart I was tempted to just drive the 20miles home
> and see how effective mobil1 is in really extreme environments.  Anyway,
> after cooling my jets for a few minutes I decided to try something:
>
> Figuring I was developing high pressure (in excess of the 8-10psi that has
> been reported as normal) in the cooling system because of the compression
> leak, I pulled my coolant pressure cap and with long nose pliers and a
> screwdriver I removed the pressure valve mechanism which then allowed
> continual venting of air out of the cooling system.  I topped up the
coolant
> in the tank, put the cap on and partly unscrewed the cap on the overflow
> tank to make sure it could bleed air out to the outside.
>
> The result is that with no pressure able to develop in the cooling system
as
> it was allowed to vent to atmosphere, I was able to drive home with only
> minimal coolant loss and temperature within the normal range (actually,
much
> more normal than when I was driving with a closed system and a compression
> leak).  All the pressure and engine gas bubbles are allowed to escape,
with
> very little coolant escaping.  I was amazed that what appeared to be a
> catastrophic gasket failure turned into just a tiny drip as long as no
> pressure was behind it.
>
> Hope this saves someone a night in the cold or an expensive tow someday.
I
> would recommend frequently checking the coolant level however as even if
it
> stops your major leak, you will loose coolant due to evaporation or
boiling
> away as the system is no longer closed.
>
> Mark
>