The TD does not have a pressurized cooling system so the maximum temperature
it can reach is the boiling point of whatever you are using for a coolant.
If it's pure water at sea level then that's 212F or 100C. Does it boil over
or does the radiator "thump" when you shut the engine off?
If you use 100% water be sure to add a good water pump lubricant with
corrosion inhibitors. This is especially important if you are using
distilled or deionized water since these tend to be more corrosive than tap
water.
A good TD shouldn't go over 190F on a 90F day. If yours does, there are all
the usual possible causes of overheating that most cars can have. However,
with the Ts there is another distinct possibility: The bypass may not be
closing when the thermostat opens. Original-type thermostats block the
bypass when they open. Since these have been hard to get and/or expensive
for some time, many have been replaced by a standard thermostat. This leaves
the bypass always open so that you never get the full flow of coolant through
the engine. Since you probably don't drive your TD much in cold weather,
it'll do little harm to block the bypass completely. This often provides a
major reduction in a TD's temperature in hot weather.
Ray G
Colorado
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