Date: Thu, 8 Sep 2005 21:00:06 -0400
Reply-To: Dennis Haynes <dhaynes@OPTONLINE.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Dennis Haynes <dhaynes@OPTONLINE.NET>
Subject: Re: overheating issues
In-Reply-To: <002b01c5b409$7c46fea0$2f01a8c0@FirstLaptop>
Content-type: text/plain; charset=iso-8859-1
The pressure cap is probably one of the most important parts of the
cooling system, yet it is often overlooked and the VW one is delicate,
and undersized. It should be tested often and replaced anytime an
overheat condition has occurred.
In order for the cooling system to function properly, it must be able to
maintain pressure. Most vehicles call for somewhere around 14-17 psi.
The pressure is required to raise the boiling point, eliminate vapor
forming, and keep the coolant in contact with the surfaces of the engine
and radiator. Even with a proper bulk coolant temperature, the internal
surfaces of the engine can be much hotter. Imagine a pot on the stove
with only droplets of water on the bottom. They quickly sizzle and the
pot will be damaged shortly. Another analogy, when soldering copper
pipes, if there is water inside, you will never get the solder to melt.
A small amount of water inside will quickly steam and the pipe will
oxidize. Absolutely dry pipes solder easily. Think cooling system full
and pressurized all is good, vaporizing, damage begins, empty, engine
gone.
Since the Vanagon water pump pulls from the pressure tank, you can often
get away with a defective cap. That is why a cap failure is not often
diagnosed. However, once conditions such as idling after a long high
speed run or very warm weather causes the temperature to rise enough
that the coolant vapor pressure overcomes the pump suction, the coolant
suddenly blows out. Next time engine is started cold, the coolant is
sucked back in, but if enough is lost, the pressure bottle is now low.
As the coolant is blowing out, think of that pot sizzling. That is the
sound of the heads and block warping while the studs are getting
stretched and the rubber gaskets are melting. The other important of
this cap is the check valve that allows for coolant recovery. If it
sticks closed, then coolant will not get sucked back from the 2nd tank.
This set up places a lot of stress on the cap since when there is no air
in the main part of the cooling system, the must open and vent some
coolant every time the engine warms up and allow for return every time
the engine cools down. If the main bottle maintained an air cushion,
then the cap would only have to vent when there was a problem.
The next problem here is the size of the vent. The cooling system may
have to handle some 300,000 btu/hr of heat. A boiler of that size would
have a pressure relief valve of 1" diameter or larger. Yet, that cap
only has a1/4" opening. That is why most cooling system failures result
in ruptured hoses, cracked manifolds, blown head gasket, etc.
Dennis
-----Original Message-----
From: Zoltan [mailto:zolo@foxinternet.net]
Sent: Wednesday, September 07, 2005 8:09 PM
To: Dennis Haynes
Subject: Re: Re: overheating issues
Hi Dennis,
Why would the cap be the culprit? How does that work? Sorry, I'm still
learning.
Zoltan
----- Original Message -----
From: "Dennis Haynes" <dhaynes@OPTONLINE.NET>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, September 07, 2005 2:45 PM
Subject: Re: overheating issues
The bubbling indicates a bad pressure cap and or combustion gases
getting into the coolant, unless you have actually over heated. Try
replacing the pressure cap. If you still see bubbling after a few
heating/cooling cycles, then most likely you are getting gasses into the
system.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf
Of John Smith
Sent: Wednesday, September 07, 2005 11:58 AM
To: vanagon@GERRY.VANAGON.COM
Subject: overheating issues
Hi Folks,
I've got a 91 Westy with about 5k on a rebuilt engine from NW Connecting
Rod
in Seattle. Everything is running great, except for a mild overheating
problem. I say mild because nothing has blown up or seized yet, and I
haven't encountered massive amounts of steam or smoke coming from the
engine
compartment. Here's what's happening:
During normal conditions in the last 750 miles or so, the temp gauge is
running at about 5/8. When I use the A/C, the temp gauge goes up to ¾,
and
the light begins to blink. Same thing happens when I'm climbing steep
hills, or in heavy stop-and-go traffic (The good thing is that the fan
seems
to be turning on normally when it reaches this level). When I pull
over,
let it cool down and inspect the van, occasionally I'll see the overfill
tank bubbling out very light amounts of coolant. I've also taken off
the
grill and felt around my radiator for any cool spots, which I did not
find.
I should also mention that the temp light will sometimes start blinking
under normal conditions as well, meaning that the temp gauge is at about
½,
driving on a flat road.
I recently took the van into the shop for a coolant system inspection.
There was a small coolant hose that needed to be replaced, which they
took
care of. After that they replaced the coolant, bled the system and
pressure
tested it- all came back normal, but it's still behaving in the same
manner.
From searching the archives, I know that this could be caused by a
number of
things, including the water pump, thermostat, and radiator, and god
forbid,
leaking head gaskets. But here's what else I know:
*The fan switch and sensor have all been replaced very recently. It
doesn't
seem like I'm having any trouble in this department.
*A good portion of the cooling system hoses have also recently been
replaced, although the radiator has not.
*The 80 degree Thermostat and water pump were replaced 5k ago when the
rebuilt engine was put in, although I suppose these could be faulty.
The only thing I can tell from all of these observations is that the
coolant
sensor is going bad, but from what I've read, that's rarely the case.
I've
also thought of the worst case scenario where the head gaskets need to
be
redone, and I have to go back to NW Connecting Rod and tell them to live
up
to their 12k warranty. Before I go this far, though, does anyone have
any
ideas on what else to check or remedy? Thanks in advance.
Cheers,
John
91 Westy
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