You know, I`ve been sitting on the sidelines most of the way through this
thread, so now, since it's stagnated into thermodynamic arguements (as far
as I can tell the second law polices itself, the conversation is reaching
maximum entropy) all I can say is
This is NOT rocket science.
TR3 thermostats are about the simplest closed-loop feedback system you'll
run into. Let me try to make the operation as simple as I can. I'm assuming
all other variables here are fixed for simplification, like forward velocity,
engine rpm, ambient temperature, coolant composition, etc...
1. The engine is cold. The thermostat is closed. The water runs through the
bypass, allowing circulation to eliminate any possible hot spots.
2. The engine heats up. The thermostat opens allowing water to run through the
radiator for cooling. The skirt moves back to block the bypass port, forcing
the water to go through the radiator.
3. The wider the thermostat opens, the more water flows through the radiator
for any given period of time, the more the water cools cooler the engine runs.
When the water gets cooler, the thermostat closes down & restricts the flow,
allowing the water to heat up. Classical closed-loop control system. The
thermostat opens and closes depending on the sensed water temperature coming
out of the engine to maintain a set temperature.
4. The engine temperature setting is done by picking the proper temperature
thermostat. The thermostat construction determines at what temperature it
It really is that simple.
There are several consequences of not properly maintaining the system.
1. If you replace the thermostat with a non-skirted type, water will rather
go through the bypass hose rather than through the radiator (path of least
resistance). The engine will tend to run a lot warmer, and depending on the
ambient temperature, overheat. This is the cause of 80% of the overheating
I've seen in early TRs here in the States. (the other 20% is lost radiator
2. If you take out the thermostat entirely, or run with a real-low
temperature non-skirted thermostat the engine can still overheat if the
ambient temperature is high enough (over 85 deg F) since the bypass is
still the path of least resistance for the water.
3. If you block the bypass (but leave a 1/4" hole in it to allow start-up
circulation and a way for trapped air to escape) and use a non-skirted
thermostat the system can be made to work great. This is the usual fix
since skirted thermostats are hard to find. This is also the fix recommended
by that TR guru Ken Gillanders of British Frame and Engine in sunny CA.
(there, I got my name dropping in) The late, great Bob Schaller would
disagree that the hole is not required in the bypass plug. Great, more
theories to argue...
4. If you take the thermostat out and block the bypass the engine will run
very cold. Nothing is in the "circuit" to restrict the heat transfer. Can
be great for racers, but stinks on the street. The engine will be below
optimum operating temperature, leading to internal carbon deposits (coking)
an increased fuel consumption. Been there, done that.
If anyone is interested I could talk a few of my crew into simulating the
TR3 cooling system during lunch on their workstations (Sun - sorry Terriann)
using the EASY5 system simulation tool (originally developed for simulating
environmental control systems). This would be overkill, but so was this
entire email message!
I'll shut up now...
Bruce "I DO rocket science for a living" Clough