Trevor Jordan wrote:
>
> 1. How do you choose between these thermoswitches? What is a good
> mid-point temperature and what effect does a wide or narrow temperature
> range have on performance?
The numbers apparently denote cut-in and cut-out temperatures in
Centigrade. The higher the cut-in, the higher the engine temperature
before the fan starts. The wider the range, the longer the fan will run
once it starts.
> 2. Most electric fans that I have seen have the thermal switch in the upper
> radiator hose. Which is the better place, upper or lower, does it matter?
Water exiting the block through the upper hose will be hotter, so the
fan will turn on earlier. At the bottom of the radiator, of course, the
converse is true, since the coolant is at a lower temperature. Fiats and
Lancias have the thermoswitch at the bottom, likely based on the
probability that such will reduce the demands on their somewhat smallish
generating system, in average driving.
> What temperature difference exists between the upper and lower ends of the
> radiator under normal operation?
A GM technical paper on cooling system design which I found last night
at work suggests that the drop for a radiator properly sized to the
engine displacement and water jacket capacity is about 7 deg. F.,
although a radiator of excess contact area and good fin design may be as
high as 13 degrees. Again, this was for diesel engines, but I suspect
the same holds true for other engines. It also depends to some degree on
airflow rate through the radiator, which is where fin design comes in.
> 3. Is it even wise to replace the engine fan with an electric fan (TRs have
> been known to overheat)?
Why not install it as a pusher in front of the radiator, and leave the
existing fan in place? Extra insurance never hurts. If you take off the
existing fan and then burn a motor on the electric fan, you're stuck....
> 4. Is it worth installing a manual override switch?
Since thermal switches do fail, and are more likely to do so when
grounding high current loads (if you hadn't planned on installing a fan
relay, too, consider it), an override switch would be good insurance.
> 5. How should the thermostat temperature relate to the fan's thermal switch
> temperature, or should I remove the thermostat <g>?
Cut-in should exceed the thermostat's rating by, say, 2-3
degrees--otherwise, the fan comes on before the thermostat's at full
open. Even so, it may be necessary to do a little empirical testing.
There's a lot of variability in thermostats... an industry study done
about a decade ago suggested that the immediate failure rate for new
aftermarket thermostats was likely the highest of any automotive part,
roughly 20% (good thing they're reasonably cheap), and I'd guess that a
typical aftermarket thermostat probably only controls engine temperature
to roughly plus or minus 4-5 degrees of its rating, on average.
I'll leave the choice of taking the thermostat out or leaving it in to
your own good judgment. <g>
Cheers.
--
My other Triumph runs, but....
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