Date:         Sat, 6 Dec 1997 15:00:53 -0400
Reply-To:     mark keller <kelphoto@BRIGHT.NET>
Sender:       Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From:         mark keller <kelphoto@BRIGHT.NET>
Subject:      Cooling System failure Prevention Idea.
Content-Type: text/plain; charset="us-ascii"

I just finished the flushing of my cooling system, then using Autobahn,and
distilled water to replenish it with. I guess that's a every two year job.
Some knowledgable people on this list have said that no one cure exisits
with regard to the corresion problem. Sevearal senarios have been posted as
to the coolant leak problems. I discussed the problem of corresion beneath
the head gasket with VW guy, who said he'd seen it on even engines that
weren't leaking, it was always present. Seeing the head gasket is basically
flexiable seal, I feel that perhaps a sealing problem is really the root
cause rather than a corrsion problem alone.

I've thought a lot about this cooling system corresion problem and am ready
to say my piece. I'd suggest perhaps a short question-aire type response in
the future to really verify this theory.  But in leiu of it I want to share
some ideas. I've tried to take every thought as far or extreme as I can to
explore the possibilities of this problem. So some effects may not be as
severe as I'm suggesting.  I'm trying to get to a point of being able to
say that thus a so a condition is to be avoided and here's how to do it. .
I realize up front that this is theroy, but I feel it explains varity of
situations I've read about here, and the design compromises of the bus and
its engine, and specifically the design of the head gasket.

My feeling is that the problem has a few componets, but the basic theory is
that coolant can be forced beneath the head gasket seals in certain
situations. I feel the temparture of the motor is a component but don't
know where the tempature is "line". Basically I saying at the very least
when the motor is first started and then run at higher than say 1500 RPMs
before the engine is warm and therefore expanded fully. High water pressure
coupled with low clamping force of the steel head studs is the major cause
for water invading the head gasket sealing area.

  I define the clamping force to be the pressure that the head nuts exert
on the heads which "clamps the cylinder head to the cylinders."  This
clamping force is dependand on the lenght of the steel studs in the block
to the bottom of the nut staying exactly the same relationship to the
distance or lenght from the cylinder head boss, which the head nut and
washer rides on, to the point at which the studs are threaded into the
engine casings.

 In other words the with two different types of metal, steel and aluminum
alloy,opposing each other to clamp the gasket together, if their respective
rates of expansion and contraciton are not identical, which they are not,
then the force that is generated by these two materials will vary with
there tempature.  Ordinarily this rate difference proses no problems within
a certain tempature range, and ordinarily this reduction in clamping force
would necessarily mean that a head gasket seal would have insuffcient force
applied to it.  However there many head gasket failures, and quite a few
possible components that excerbate the dissimilar metals expansion and
contraction.

Additionally the Subaru engine design of the 6 cyl I looked at had the
engine case and cylinders cast together, and thus could use a shorter
studs, thus cutting down the total amount of contration and expansion that
the head gasket had to compensate for.

  The other conditions I discuss cover the susceptability of the dissimiar
metals used to construct the motor to weaken the clamping force on the head
gasket, and uniquness of high revving engine, coupled to a requiment for
the water pump to push water over very long cooling circuit.


COLD ENGINE

I'll try to discuss this in an orderly fashion. The VW guy said that the
Head gasket water leak "recalled repair" was just to "retorqe the heads to
a higher torque setting.  Knowing that the engine head gasket relys on both
the expansion and contraction rates of all of the various metals to be
similar in its operating range. The metals being used are:engine case,
magnisium,and alumunin, steel head bolts, and aluminum cylinders. Once the
engine is at operational tempature expansion completes the total clamping
force, the engine design of being opposed with removable cyliniders
maginifies this because there is a greater distance between heads and block
attachment points for the studs, and thus a longer distance at which a
dissimlar contraction rate to make a difference.

I feel a second componet HIGH water pressure. The vanagons water pump
impeller is designed to generate a lot coolant flow  and overcome the much
larger friction area of the  front radiator location and hoses to and from.
Also the water pump is required to provide adequate coolant flow water pump
operates over a very wide operating range engine rpm. It would be easy to
state categorically that Anyone starting up and driving a cold engine would
be over 3000 RPM with a minute of start up..  The thermostat spring is
supposed to relieve  pressure build up, but again on first start up cold
soaked engine in low ambient tempatures with the operator going to high
RPMs, I feel that this is a good bet that the water pressure inside a cold
engine is much higher than at normal operating conditions. To a smaller
degree but still a fact, the suction caused by the piston's intake stroke
coupled creates a greater still pressure differential between water and
head sides of the head gasket.

A second theroy would be that the "errosion" of the head surface occurs
first, when water gets in between the head and the heat of cylinder forces
steam to pit the head surface repeatedly.  The corrosion then would just be
evident when the gasket  seal fails  completely, and coolant is present all
the time. I don't really buy the corresion theroy all the way, since
reports of "corresion" occur in well maintained vehicles.

Another caveat is failure or restriction anywhere in the cooling system
that makes the water pressure abnormally high.

Another problem, depending on the actual engine temps at which the clamping
force of the head bolts is reduce by dissimilar metal contration, is that
fact the the VW engine dissipates heat quickly, and cools down rather fast,
plus that the radiation is not in "warm" engine compartment like common
vehilce, and loses heat quicker too.  If the dissimilar metal contraction
occurs at a relatively high  tempature, then Stops and starts of say a half
an hour or so could be enough time for the engine to get cold enough for
the clamping force of the head gaskets to be below operational values.

I guess this last theory has probably been a focused fix for sometime since
its a passive one.  Better resiliencey of the actual head gasket. My guess
is that the orginal ones failed because of shrinkage, or hardening.

In conclusion, I suggest that a simple water pressure guage would be a
better way to gain information about when the engine is prone to water
intrusion under the head gaskets.  My basic suggestion it to let the engine
idle until the at least the temperature guage shows a movement before
driving at higher RPMs.  Depending on ambient tempatures and driving /time
stopped/ cycles, and the actual temperature where the clamping force is
reduced, allow for warm up before operation at high rpms.



Sincerely Mark
91 Carat WE
"Lazarus"