Date:         Mon, 13 Apr 1998 18:45:04 -0400
Reply-To:     Martin Jagersand <jag@CS.YALE.EDU>
Sender:       Vanagon Mailing List <Vanagon@vanagon.com>
From:         Martin Jagersand <jag@CS.YALE.EDU>
Subject:      Re: Diesel cooling problem advise needed
Comments: To: vanagon@vanagon.com

> Told you earlier this week my temp gauge ('81 diesel) is fluctuating =
> between high and low.
>
> The overflow tank was up to level so I did not expect anything wrong =
> with the amount of coolant. Today I looked in the container under the =
> lid and found it to be nearly empty. It put approx one litre in. Now the =
> gauge does not fluctuate so strongly. I fear however more is (seriously) =
> wrong.
>
> For those expert on the diesel I have the following questions:
>
> 1. How come the overflow tank is full and tank under the lid empty? =
> That's not normal is it?
>
> 2. When I started the enigine and looked in the tank under the lid, the =
> coolant looked frothy. Is that normal or a symptom of a very bad problem =
> inside the engine?

When you have air (or other gas) in the cooling system, the air/gas
will go through pumping cycles each time the engine is taken
from cold-warm-cold. When going from cold to warm the gas expands.
This pushes coolant and/or gas out from the cooling sytem into the overflow
tank. In reverse, when the engine cools after having been warm
coolant is sucked back in.

In the best case your problem is simply a poorly bled cooling system.
That means that a lot of air was left in the system last time
when the coolant was changed.

However, you potentially have a problem which combustion gases
in the cooling system. In this case most likely the head gasket
is leaking, and possibly the head is warped. Combustion gases will
leak into the cooling system and displace the coolant.

A more remote possibility (but I've seen it happen) is that your
coolant is boiling despite the temp is not overheating. Your
thermostat regulates the temparature near the thermostat to near
87 Celcius, but that doesn't mean the temperature is an even 87 degrees
everywhere. There are always local hotspots. In a properly functioning
cooling system boiling is prevented by:

1. The antifreeze not only lowers the freezing point but increases
the boiling point.

2. In a non leaking cooling system, there is no room for the volume
expansion caused by boiling. Instead the pressure will rise (up to
the pressure cap limit), effectively increasing the boiling point
further.

I would start checking the easy things: Bleed system (see your manual
or the list archives, pressure cap, leaks. If despite careful bleeding
and no external leaks, gas still appears in the system, suspect the
head gasket problem.

Good luck,
Martin

PS For you diesel owners, (and other interested) there is a diesel
mailing list you are welcome to join. Instructions are on the links
page though the URL below. The diesel list tends to be more technical
then the Vanagon list, but the listmembers are every bit as friendly.

--
Martin Jagersand                 email: jag@cs.yale.edu
Computer Science Department             jag@cs.rochester.edu
Yale University

        Slow down and visit the VW diesel Westy page:
          WWW: http://www.cs.rochester.edu/u/jag/vw
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