Date: Sun, 11 Jun 2000 08:10:34 -0700
Reply-To: t <vbob@PRIMENET.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: t <vbob@PRIMENET.COM>
Subject: Re: Cooling System Weirdness
Content-Type: text/plain; charset=us-ascii
Not stupid questions.. although contrary to popular belief, those type
questions do exist...
The reservoir tank, the one you fill from the back, is not pressure
tight. The hose feeds into the bottom of the tank and therefore has
fluid available at all times unless you let it get low. The expansion
tank is pressure tight. From my experience, it does not blow excess air
into the reservior tank. Why? I dunno.
Your steps here are, bleed the system according to Bentley. fill the
reservoir tank and keep it filled. Watch for bubbles in the expansion
tank (especially at 2000 rpm and above), Keep after the system for a
couple of days getting the air out of the system. Keep the reservior
filled to the line.
Pray to whatever supreme being you worship that you haven't induced head
gasket failure by letting it get too low.
Ask lots of questions.
tim
Marc Perdue wrote:
>
> 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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