Date: Sat, 22 Sep 2001 08:15:46 -0500
Reply-To: Larry Alofs <lalofs@ENTERACT.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Larry Alofs <lalofs@ENTERACT.COM>
Subject: Re: head gasket problem ?
Content-Type: text/plain; charset=us-ascii
The analysis below is very good. I would add one thing.
When heated, gases expand much more than liquids which expand more than
solids. If you have any significant amount of air or other gases in your
radiator, its expansion when the car is thoroughly warmed up can cause more
expansion than normal. Since air in the radiator is at the high point in the
system, it must be released via the bleeder bolt whenever troubleshooting etc.
is done.
Larry A.
"Michael A. Radtke" wrote:
> Hello,
>
> I cannot guarantee the accuracy of this information, but this is the
> workings of a pressurized cooling system as it was explained to me.
>
> First consider the system as one large container. If the container and its
> content get heated, does the pressure increase? Yes, if the contents
> expands at a greater rate than the container. No, if the container expands
> faster than the contents. If we consider the first case, how much pressure
> increase can be expected? Well, much of the container is fairly flexible,
> like the hoses and the thin tubes in the radiator and heater cores. So,
> even if the coolant expands faster than the container, the pressure
> increase would be small.
>
> So then, where does all the pressure come from?
>
> Head gasket leaks!
>
> As it was explained to me, even the best head gaskets leak ... a little.
> So, as the engine runs, the cooling system pressure gradually builds until
> the pressure cap relieves the pressure. But, the gasses leaked from the
> head gaskets are supposed to accumulate at the pressure cap, so coolant
> doesn't leak, rather these gases leak.
>
> So why then is the overflow of the coolant recovery tank an indicator of
> bad head gaskets? Well, if the head gasket leaks badly enough, instead of
> just gasses at the pressure cap there gets to be foam. So, as the pressure
> gets relieved, coolant flows to the coolant recovery tank along with the
> gases.
>
> So, the bottom line is that a little leak is OK, a big leak is not.
>
> If the pressure cap opens at too low a pressure, and that's often how they
> fail, the coolant boils in the hot spots of the engine even at normal
> operating temperatures. The resulting foam carries coolant out the
> pressure cap just like a bad head gasket leak.
>
> So, I'd try the inexpensive pressure cap first before the expensive engine
> repair.
>
> Thanks for listening,
>
> Mike -- Phoenix Arizona (something like Egypt)
|