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Thermostat bellows type TR2-4A. This thermostat has a ring around the outside that is intended to block off the bypass port during normal running. This port is connected by a short hose to the water pump and circulates water around the engine without going through the radiator during the warm up phase.

The shortfall of this system is that some water will escape past the ring during normal running and bypass the radiator, compromising the maximum cooling available. Here at RevingtonTR we favour an alternative approach. Given that TR owners these days are careful drivers and are not likely to drive hard before the engine has warmed up the bypass system can be blocked off and a modern (much cheaper) thermostat used. The three types normally used are GTS102, GTS104 and GTS106 with various temperature opening characteristics. The bypass flow can be blocked off by a plastic cap or a fashioned piece of wood jammed into the water pump entry port where the bypass hose attaches. Whatever is used to block off the port, ensure it is either suitably tapered or has a rim so that it cannot be sucked into the water pump. See below for thermostat options

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