Allan,
Based on some Tiger cooling tips that were submitted this summer, I
installed a new thermostat (195F of course) in which I drilled three 1/8"
holes. I was just guessing as to the appropriate size hole, but 1/8"
seemed small enough to be rather inconsequential as far as total flow, but
enough to allow easy fill of the radiator plus allowing any air to pass
through. I am somewhat surprised by the result and thought you and others
might want to know my experience. In addition to changing the thermostat,
I also partially blocked the bypass by putting a piece of gas hose inside
the bypass hose. The idea was to get better pressure and flow through the
radiator at idle which is the only condition where I ever have any heating
problem that requires me to turn on the electric fan. Anyway, much to my
surprise, with only these three 1/8" holes the water still runs about 170F
or about 100F over ambient on the freeway. Sitting in traffic, the
temperature has gotten up to the 195F and a little beyond, but seems not to
need the electric fan (ambient probably about 75F). Of course, it also
takes a little longer for the temperature to come up than with the previous
(180F) thermostat.
I was going to yank the thermostat out and redo it with maybe only one 1/8"
hole, but decided to go to the San Diego Concours at Torrey Pines instead.
Also, I was a little curious to explore the behavior of this thermostat
under my usual driving conditions. I like the idea of having a restriction
to give good pressure inside the motor rather than across the radiator, but
I also like having a thermostat that gives quick warmup and stable
temperature. Based on this experience, if I wanted to go with just a
simple restrictor, it looks like about a 1/4" hole would be big enough to
allow sufficient water flow. This is way smaller than typical restrictors
which are probably 5/8" or 3/4". I'm sure the minimum size that still
allows good cooling will depend on factors such as how much pressure your
water pump generates and maybe whether you have a single, double, or triple
pass radiator (mine is a three pass).
So where do I go from here? I think that as the weather cools I will not
be happy with my motor running at or below 170F, so will want to change
something, probably go to just a single hole. Thinking about all the
things I'd like the thermostat to do, I think what's needed is a two-stage
thermostat. The first stage would open at around 185F and flow through a
fairly serious restriction on the order of 1/4" - 3/8" in diameter. The
second stage would open up at a much higher temperature, say around 220F or
so. This would take care of the sitting at idle with too little pressure
to get adequate water flow situation and be kind of a "when all else fails"
open all the stops strategy.
Don't know if any of this information will be useful to you as you redo
your cooling system, but thought I'd toss it out there in case your
interested.
Bob
Bob Palmer
UCSD, AMES Dept.
rpalmer@ames.ucsd.edu
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