Date: Sun, 11 Jun 2000 11:02:00 -0400
Reply-To: Marc Perdue <marcperdue@ADELPHIA.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Marc Perdue <marcperdue@ADELPHIA.NET>
Subject: Re: Cooling System Weirdness
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For the record, I'm posting this response to the list in case a) people want to see
just how much of a newbie I really am; or b) in the hopes that someone else may
actually benefit from the troubleshooting steps that I'm taking . . .
Thanks for the good suggestions Larry. Now, let me see if I understand this
correctly . . . the cap on the expansion tank operates as a sort of two-way
pressure relief valve. If the pressure is too high in the expansion tank the cap
valve should open and blow air into the coolant reservoir. If the pressure is too
low in the expansion tank, i.e., the engine has cooled down and sucked the coolant
back into it, then the cap valve should open and pull coolant from the reservoir.
Is this basically the way the system works? If so, then the coolant reservoir
would have to be airtight too, correct? What happens if some bozo, namely me,
doesn't keep enough coolant in there? Wouldn't you draw a vacuum on the coolant
reservoir? What relieves the negative pressure in this scenario?
Now, regarding a leaky hose connecting the expansion tank and reservoir . . . if
the leak were bad enough, then I would expect to see that the volume of coolant in
the reservoir would stay the same, because the expansion tank would always be
sucking air in a negative pressure situation. I went out to check this and found
that my coolant reservoir was empty. Hmm . . . I'd say that I probably don't have
a leak in the hose, even though the hose connection at the expansion tank doesn't
seem too terribly tight. Yet, there was no vacuum in the coolant reservoir when I
took off the cap to add coolant/water, so there must be a leak somewhere, yes?
My apologies for burdening the list with a boatload of stupid questions. I am
simply trying to understand this system better so I can maintain it better. Thanks
for your patience, understanding, forebearance, and, most of all, thanks for the
help!
Marc Perdue
Lawrence Johnson wrote:
> Marc, I suspect that the cap on the expansion tank is either plugged or damaged
> and is not opening at the correct pressure (14 lb. ?). If it were opening
> correctly then that pressure that you observed would have opened the valve in
> the cap and forced the entrapped air into the overflow reservoir tank.
> Also, make sure that the hose from the expansion tank to the overflow reservoir
> tank is air tight and connected securely. If it is not, then when the engine
> cools and the expansion tank begins to draw coolant from the overflow reservoir
> tank, instead of drawing coolant into the expansion tank it starts sucking air.
> -Larry
>
> Marc Perdue wrote:
>
> > <snip>On the way back Sunday evening, with the outside temp at about 70, the
> > coolant level red light came on and started blinking. Having heard (okay,
> > read) the horror stories here about blown engines, I pulled over immediately
> > and started checking everything. Temp needle was at about one-third, heat
> > was about normal given there's no working fan, engine didn't feel very hot,
> > and the reservoir was on Max.
> >
> > After I turned the engine back on, the light stopped blinking . . . until we
> > got a couple miles down the road. This time I pull into a gas station and
> > start flipping through the manual. This is the part where I find out about
> > the coolant expansion tank, inside and to the left of the coolant reservoir,
> > where the coolant level sensor is. Aha! The level is at minimum! Of
> > course!! Problem is, how did it get there?
> >
> > I carefully pulled the small hose that connects the reservoir to the
> > expansion tank . . . no pressure and nothing leaks out . . . so far, so
> > good. I start to loosen the cap on the expansion tank when all of a sudden
> > there's a hissing sound and the expansion tank fills rapidly! I tighten the
> > cap and replace the reservoir hose and drive home with no further incident.
> > What is going on here? It seems that the expansion tank built up enough
> > pressure to prevent any further coolant coming in from the reservoir, but
> > what caused the pressure buildup to begin with? Is this a symptom of a
> > cooling system that needs to be burped?
> >
> > I'm looking forward to finding an answer to this one. It had me a little
> > nervous there for a while . . .<snip>
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