overflowing coolant

Brett Dikeman brett at cloud9.net
Mon Aug 19 23:15:55 EDT 2002

At 11:50 PM +0000 8/19/02, walian at att.net wrote:

>  Can replacing the coolant with straight water make the
>expansion tank overflow?

Yes.  Been there, done that 3 days ago.  See below.

>  I have just put the timing
>belt and refilled the radiator with water. I drove to
>work this morning(20 min) and noticed that the car was
>low on coolant(water) a few hours later when I went to
>run an errand the emergency light came on and the
>expansion tank was completely empty. I filled it to the
>brim with water and drove home, no problems. I just
>came back from a store and the radiator expansion tank
>is now leaking water. Can this be due to straight water
>or a bad thermostat which I just replaced?

Probably more likely that your expansion tank cap is leaking
pressure, so that's allowing the water to boil.  On my 200, idling,
it would spit out almost a quart in a matter of seconds if I left the
cap off; with the cap on, it would idle for 20 minutes easily without
boiling over.  I have a brand new cap that doesn't leak, period...and
that's probably the difference here, though checking(or simply
replacing) the thermostat probably isn't a bad idea- they do go

The caps are about $5-ish at any VW or Audi dealer, practically
guaranteed to be in stock.  Still, you shouldn't be running water all
the time(I was only doing it for 10-20 minutes to flush the system.)
I can't imagine the thermostat being pricey either.

Don't run "just water" in a car for anything more than just temporarily:

a)zero corrosion protection and in fact just the opposite, especially
with distilled water(or worse, deionized water which is -very-
b)zero lubrication for the water pump
c)zero freezing protection(of course)

"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin

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