This whole process was taken on because of the difficulty that I have
experienced in getting my 1.6L, 67.5 Roadster to run in the temperature
range in which I had expected. Understand that I live in central Texas,
where it is not unusual for the air temperature to run over 100 deg. in
the summer.
First, a bit of "how the cooling system is supposed to work" theory.
The water in the engine pulls combustion heat out of the cylinders and
head. The thermostat controls the water flow rate through the system
to allow the engine to get up to operating temperature more quickly
and then control the temperature of the engine once operating temperature
is reached. The radiator gets rid of some of the engine heat as the
water flows through it. If an engine produces more heat than the radiator
can get rid of, the engine temperature will rise. The amount of heat
that the radiator can get rid of is generally more than the engine can
produce, thus allowing the thermostat to control the engine temperature,
rather than the radiators dissipation controlling engine temperature.
The heat in the radiator is gotten rid of by airflow through the fins
on the radiator. When the vehicle is stopped, or traveling less than
about 20MPH a fan is required to move the air. This fan may be either
electric, or engine driven. On most vehicles the ram effect of air
entering through the grill produces enough air flow to get rid of the heat
without a fan. This ram effect is not enough on our roadsters to cool
the radiator!
I have experienced over temperature conditions on my roadster since I
bought it. I have cleaned the radiator, replaced the thermostat, and
hoses. The factory scoop is in place at the bottom of the radiator.
None of these changes produced acceptable temperatures.
I tried replacing the engine driven fan with an electric fan, but it didn't
help, on fact, the temperature rose a bit. (No fan shroud). I tried
both pusher and puller mounting, but the 14" fan just couldn't keep up
with the cooling requirements. The electric fan was on a thermostat that
was set to turn on when the radiator inlet temperature reached 190. On
the road the temperature would still run about 190, with it dropping slowly
at stoplights. I finally bypassed the fan thermostat and that allowed
the fan to get a bit more control over the heat, but it still didn't supply
enough cooling.
When I turn on the heater (fan on high) the engine temperature drops about
10 degrees. This seems to say that the radiator is not dissipating enough
heat for whatever reason. It may be that the radiator is crudded up, not
enough heat transfer area, or the air flow through the radiator may not be
high enough. I removed the 3 row radiator that was in the car when I bought
it and replaced it with a high efficiency , 2 row radiator. This change
brought the temperature down a few degrees, but still not enough.
I tried adding an air dam between the radiator and the cross member to cause
more air to flow through the radiator, rather than around it to increase the
ram effect, but it didn't help.
Next I replaced the water pump. The original one was from Auto Zone. I
installed a Datsun pump and the temperature dropped another few degrees.
(Generally, I wouldn't have done this because I figured that the problem
was external to the engine because of the temperature drop when the heater
was turned on, but the rear pump cover gasket started leaking so it had to
come off any way.)
I removed the electric fan and re-installed the engine driven 7 blade fan
with fan shrowd and the temperature came down to about 180!
The temperature would stay at 180 solidly in all driving conditions except
when the temperature was above about 104, a bottle of water wetter took
care of that!
Water is a better heat conductor than antifreeze, so the lower concentration of
antifreeze the better the heat conduction. Redline recommends an antifreeze
concentration as low as 15%, so I set mine to protect to +20 degrees -
remember, I live in Texas and we don't see really low temperatures here in
the winter!
The only thing that I don't like about this configuration is the amount of
noise the fan makes. It shounds like the 240Z I used to own! I really liked
the lower noise lever of the electric fan! I may try replacing the 7 blade
fan with a 4 blade fan to see if it still provides enough air movement while
reducing the noise.
Today it was 112 and the engine temperature sat steady at 180, whether I was
running 65 down the road, or sitting at a stop light. Things are now MUCH
cooler in Texas!
Other things that may be causing excess heat:
I don't know how much crud is built up in the block. I bought this car
a year ago and have no idea how much time is on the engine.
The head has been milled past the limit. The compression ratio is very
high. This could cause higher combustion chamber temperatures than normal.
I have another head to put on the engine, but haven't gotten to it yet.
Maybe next week I 'll get to it.
--
- Support Habitat for Humanity, A "hand up", not a "hand out" -
Pat Horne, Network Manager, Shop Supervisor, Future planner
CS Dept, University of Texas, Austin, Tx. 78712 USA
voice (512)471-9517, fax (512)471-8885
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