Phew! The thread that won't die!
For what it's worth, in my early TR4 (TR3 style radiator) I use a 160
degree non-skirted thermostat. I don't have a plug or restrictor in the
bypass. My temperature gauge sits at about 185 degrees F no matter what
the outside temperature. I used a 180 deg F thermostat for about a year,
but that raised the normal running temperature to a bit above 200 degrees
which caused premature exhaust valve seat erosion and cylinder wear.
Over the years I've used the same type of thermostat in a whole gaggle of
T-Type and Y-type MGs. The cooling system in those cars is similar to
that of the TR3/4, and also originally used a skirt to close off the
bypass. With the exception of a really badly clapped out YA Saloon, I
never had overheating problems in any of them.
In most cases of overheating the cause is poor engine condition, poor
tune, a clogged radiator, or clogged coolant passages in the engine. No
amount of thermostat/bypass voodoo will compensate for an engine or
cooling system in poor condion.
Since this thread seems fated to go on forever, let's at least clear up
some of the misconceptions that have surfaced in it:
In a pressurized cooling system the pressure is created by the expansion
of the coolant as it heats up, not by the water pump. The water pump's
only function is to keep the coolant moving through the system.
A thermostat's primary function is to help the engine reach and stay at
normal operating temperature rapidly, not to boost heater output.
An engine wears much faster when it is cool than at normal operating
temperature. For that reason it is never a good idea to eliminate the
thermostat. In the interest of long-term reliability, you want to get the
engine up to normal operating temperature as quickly as possible.
The skirted thermostat is a nice idea, but it isn't really necessary. The
TR2/3/4 cooling system layout is no different from that used in most cars,
and in the overall scheme of things automotive the skirted thermostat
favored by many BritCar manufacturers of the time is an oddity, not the
norm.
Unless you eliminate the thermostat (NOT recommended), do not block off
the bypass completely. With a blocked bypass there will be no coolant
flow through the engine until it heats up enough to open the thermostat.
Some parts of the engine (around the exhaust valve seats, for example)
heat up very rapidly. With no coolant flow, that can cause localized hot
spots, coolant boiling, and rapid wear.
If you must mess around with the bypass, restrict it rather than plugging
it completely. A restrictor plug with a 1/4 or 3/8 inch hole will allow
adequate flow through the engine when the thermostat is closed, and will
decrease the potential for flow through the bypass when the thermostat is
open.
All non-skirted thermostats are not created equal. If you compare brands,
you'll see that some have larger valve discs than others, and will
therefore flow more coolant when wide open. This in turn helps to
decrease flow through the bypass, since the coolant will flow in the
direction of least resistance.
If your new thermostat doesn't already have one (most don't these days),
drill a 1/8 inch hole in the valve disk near its outside diameter. When
you install the thermostat, rotate it in the housing until the hole is at
the top. This will allow air to bleed out of the engine as you fill the
cooling system.
The major failing of the TR2/3/early 4 cooling system is the radiator,
which is too small and has inadequate air flow through it. If you ever
need to have the radiator rebuilt, use a modern high-efficiency core, and
eliminate the hole for the starting crank to maximize surface area.
Keep the radiator shroud in place. It helps to maximize the flow of air
through the radiator. If originality isn't a concern and you do a lot of
stop and go driving, use a multi-bladed plastic fan from a TR260 or TR6 to
maximize air flow at slow speeds. The original four-blade fan isn't a
great mover of air. Even better, use a thermostatically controlled
electric pusher fan mounted in front of the radiator and do away with the
engine-driven fan. An engine driven fan actually blocks air flow somewhat
at high speeds.
Keep the cooling system clean. Boil it out once a year with a two part
(acid/caustic) cleaner, flush it thoroughly (reverse flush if you can).
The "one step" cleaners aren't very effective, and a simple drain and
refill is almost useless.
Use a 50 percent antifreeze solution all year. In addition to lowering
the freezing point of water, antifreeze also raises the boiling point. It
also contains corrosion inhibitors, which help to keep scale and corrosion
from decreasing the efficiency of your cooling system. True, plain water
transfers heat better than a water/antifreeze mixture, but the difference
is insignificant and is outweighed by the benefits of antifreeze. If
you're really concerned about maximizing heat transfer, add some "Water
Wetter".
Use a pressure-type radiator cap. A pressurized cooling system raises the
boiling point of the coolant. Most TR3s came with 4 psi caps, TR4s with 7
psi caps. The 7 psi cap is suitable for all, but make sure it is the
correct size. On the TR2 and TR3 and early TR4s with the TR3 radiator the
cap is deeper than on later TR4s. The later cap will fit the earlier
models, but will not seal, resulting in an unpressurized system.
Keep the engine tuned up, and make sure your distributor's mechanical
and vacuum advance are working correctly. Too lean a mixture and/or too
little ignition advance are major causes of overheating.
If a compression test shows valve sealing problems, get it fixed. Blow
bye past worn valves or valve seats contributes to overheating.
-----------------------------------------------------------------------
Chip Old 1948 M.G. TC TC6710 NEMGTR #2271
Cub Hill, Maryland 1962 Triumph TR4 CT3154LO (daily driver)
fold@mail.bcpl.lib.md.us
If cars had evolved as fast as computers have, by now they'd cost a
quarter, run for a year on a half-gallon of gas, and explode once a day.
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