[Vwdiesel] coolant questions

[Val Christian]

Your head gasket may be leaking under high pressure, probably with the 
engine cold at startup.  As the engine heats up, the leaking may reduce.
The system stays pressurized at the cap pressure, and may depressurize 
as it cools, when the gas is mostly watervapor.  When it's exhaust 
gases, it doesn't shrink as much when it cools.  Also pockets
of gas in the engine will push the coolant out.

You might do an experimental run with the pressure cap off, and keep
adding fluid (i'd dilute to something like 30/70h2o, to save money) 
and see what happens as you idle and lightly run the engine.

I'm thinking you're right...head gasket.  Over the years Ive seen dozens 
of hg fail on VW, and yours is behaving that way.

Having said all that, you want to make sure that you don't have air in the
system, and that you are not getting hot spots, and that the cooling system 
gets every chance to work properly.  Run it unpressurized, and top it off,
and then see what happens.  Meanwhile, I'd plan the HG replacement.
It's not too bad of a job, but you will probably want to have the head 
serviced while it's of.  With no complications, and not counting time 
going to the machine shop for the head, I figure about 4 to 5 hours 
for the job.  First time doing it, and I'd budget 15 or 20.  Perhaps
others can chime in with their experience.

Good luck.

ps: Forget the headgasket in a bottle repairs.  Gassers may have a 8:1
vs a 22.5:1 compression ratio.  

pps: Before you pull your head, if you do, please do a compression check
on a reasonably warm (100F??) engine.  Then you have a baseline.



> 
> I had a high temp indication and found the reservoir empty. I filled it and
> still had a high temp indication. When I checked the reservoir it was under
> pressure after sitting all night and blew coolant all over the ground when I
> took off the cap. I siphoned off some coolant to get the level below the
> return line from the radiator. It was real cold the next night and the gage
> said it was running hot again. When I checked he coolant, it was gone from
> the reservoir.
> 
> I filled it again and started it and there is not immediate pressure, like
> I'd expect from a blown head gasket. It this how a dead thermostat works?
> 
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