Date: Thu, 06 Jun 1996 06:39:20 -0700
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: jwakefield@4dmg.net (john wakefield)
Subject: Heat handling design error help
I believe the design weakness in VW water jacketed motor installations
most commonly responsible for failures is their marginal heat rejection
system. Not only were heat rejection design errors common, but the gas
motors developed a fearsome reputation for being easily damaged by
over-heat conditions that other power plants would typically accept.
Chrysler purchased and remarketed these motors with minor modifications
in their early Plymouth Horizons and Dodge Omnis, and both kept their own
records which each revealed unusually high incidence of over heating
induced damage. Their cooling systems were quite conventional, and
remained nearly the same after they began using their own power plant,
but that change ended the unusual incidence of over heating induced motor
failures.
Now I don't propose to address the causes for these motors' ungraceful
sensitivity to occasional over heating, but I do think this group has the
experience, insights, and talents necessary to develop a list of after
market design improvements that can greatly lessen chances that van type
vehicle owners will experience this violation of their reasonable
expectations.
Some well known or suspected design errors are:
1) Weak and failure prone water pumps. A more aggressive impeller design
or what ever is required to increase coolant flow would be helpful.
Bigger, spun faster, tighter clearances for improved idling flow,
stacked?
2) Water passages to and from the radiator from the motor were too small
for their length on early units. I think this list's FAQ archive seems to
suggest they were enlarged on vans after about 1983.
3) Both progressively staged control switches for the two stage fan were
specified with values that are either too high or were inappropriately
located, and should be replaced by lower temperature switches or
relocated to the motor or both. Keeping the radiator within specified
range is NOT an intelligent design goal, keeping the engine within good
safe design range is an intelligent design goal. So these two radiator
mounted sensor locations appear suspiciously like design errors.
4) The cooling system is already marginal without reducing and preheating
the remaining air flow to the main radiator due to air conditioner
condenser location. For that reason, alternative condenser locations
should be examined. An archive description of an engine transplant
mentions that a rear wheel well area with high air flow successfully
accepted an air to fluid heat exchanger. I'd fear impact damage, dried
mud obstruction, and creating another location that would discourage
frequent visual inspection and maintenance. I am very attracted to the
two high side rear loover openings, and would like to hear others
thoughts about this. If an electric fan is needed, unloading the
engine's main radiator would justify it.
5) The current inconveniently accessable bleeder valve for the radiator's
top discourages frequent checks. An extending tube leading to another as
high or higher final valve? Repositioning the current valve to accept a
through-the-grill removable extention handle?
6) Oil cooling capacity from oil heated surfaces outside the engine are
too small and not optimally exposed to air flow. It's always better to
pull a btu from oil than the water based coolant. A loover sized heat
exchanger in the air dump?
Now I know these thoughts aren't exhaustive but most are conceptually
valid. There's no excuse for designing a power plant installation that
can't handle its peak thermo loads with some reserve. What ideas give
the most cooling bang per buck and per unit of required time? Examining
the diesel owners manual reveals that they did not offer air conditoning
on diesel Vanagons (a sub set is Westy) because Multiple guess for Car
Talk: 1. Insufficient horsepower to pull additional load? or B.
Insufficient cooling system reserve capacity? *************** Those of
you who said B are correct. :>
Give some input. How could we increase hot conditon coolant flow,
better control the OEM two stage radiator fan, better position air
conditoning condencer(s), improve radiator bleeder valve access, improve
oil heat radiation, or what ever occurs to you.
Thanks for listening and considering. In a day or two, you may
have thought up an elegant piece to this puzzle. Please chew on this
mind candy.
John Wakefield