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Date:         Mon, 7 Jun 2004 21:59:30 -0500
Reply-To:     John Rodgers <jh_rodgers@BELLSOUTH.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Rodgers <jh_rodgers@BELLSOUTH.NET>
Subject:      Re: Overheating problem
Comments: To: Jack Keegan <keegan@CECS.PDX.EDU>
In-Reply-To:  <000f01c44ce0$abe73c60$efdafc83@ds.cecs.pdx.edu>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Jack it's been a while since I owned an 85 model, but for my 88 GL it works like this. Hot or cold, the Expansion Tank should remain full at all times. As the engine warms the coolant and it expands, the increasing pressure on the system caused by the expansion will open the overflow cap and push the coolant into the Overflow tank. The expansion should never be so great as to push coolant out of the overflow tank onto the ground. During normal operation, as the engine cools after being shut down, the coolant shrinks, and the atmospheric pressure pushes the coolant back through the tube, through the expansion tank overflow valve, and back into the expansion tank. This process never introduces any air into the system. However..........................

If exhaust gases are escaping through a head leak into the coolant, the expanding gases will pressurize the system, forcing lots and lots of coolant out into the overflow tank and even out of the overflow tank onto the ground. A bubble of gases will be trapped in the expansion tank and the tank cannot/will not refill from the overflow tank.

The other possibility - and the one that existed on my van - are the cracks in the expansion tank. If there are cracks, the cracks may draw air and bypass the overflow valve. If this happens, the overflow tank will stay full as the coolant shrinks and air is drawn in through any cracks, filling the expansion tank with air.

One final note. Check your thermostat. Heck, put a new on in, then check your system. I had a bad thermostat,stuck closed, and as the coolant heated, the expansion would blow the coolant level sensor right out of the tank, ruining the thread of both the tank and the sensor.

Hope this helps.

John Rodgers 88 GL Driver

Jack Keegan wrote:

>I have an 85 GL with the 2.1L engine and a few overheating questions for >any of the wise and experienced folks on this list. > >Background: I took it in for a fuel leak and the mechanic found a >coolant leak, and it is the all-too-common head gasket, but it's not too >serious at this point, and more importantly, I'm broke, so it's going to >have to wait. He also found that there was no coolant overflow tank >behind the license plate, and that the cap on the main tank was the >wrong one, so he installed an overflow with the right cap. > >After that, the temperature light started flashing now and again. The >temp gauge would immediate go to max as well, even if the van had been >sitting for an hour or so. If it started flashing while driving, >turning the heater on would immediately solve the problem, and it would >stop flashing and drop back down. > >Well, the last time I drove it, (it's not a daily driver, so a couple of >weeks had passed) the light started flashing, and the heater didn't help >right away, so I stopped. I looked at the engine, and the main coolant >tank was really low, but the overflow was overfull. When the engine >cooled down, I opened the main tank to add coolant, and as soon as it >was depressurized, it filled up, not all the way, but mostly. So I added >coolant and went home without problems. When I looked closely, I found >a tiny little crack in the main reservoir. > >After it cools to RT, the main tank is basically full, and there is way >too much coolant in the overflow behind the license plate. > >Could the crack in the main reservoir not allow the coolant in the >overflow to be sucked back into the main tank? It seems like it is only >going one way-into the overflow. Would replacing the main reservoir or >sealing the crack help the problem? If I decided to try sealing it, >would I want to drain the overflow tank some before using, because it is >way above the max line at this point? What is the best way to do that? > >Also, the coolant leak was really minor before the overflow tank was >added, and we never had overheating problems. It seems to have gotten >worse, a couple of drops of coolant on the pavement overnight vs a 2-3 >diameter spot. Would adding the overflow make the head gasket leak >worse? It also doesn't seem to leak all the time. I'll get a little >spot every 3rd or 4th time I drive it. > >Any advice on this is appreciated. > >jk > > >


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