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Re: TR3 Thermostat

To: triumphs@Autox.Team.Net
Subject: Re: TR3 Thermostat
From: cloughbt@batman.flight.wpafb.af.mil (Bruce T. Clough)
Date: Thu, 27 Feb 1997 07:39:17 -0500
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 
opens.

                      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 
shrouds!)

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

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