Thermostat housing TR3A /TR4

[Menno van Rij]

Hello all,

 

There's an early TR4 engine in my TR. The thermostat housing is warped somehow: the front part of the housing (where the radiator hose is attached to) doesn't seem to fit correctly to the back part of the housing.

I've found someone who's willing to sell my an other housing. But, I remember to have read somewhere that there's a difference between a TR3A housing and a TR4 housing: the exit for the bypass house seems to be different: the 3A's house has an round bypass exit, the TR4's has an square exit. All of this has to do to restrict the flow of the water through the bypass hose: when to much water passes the bypass, there's shouldn't be enough water going through the radiator, thus restricting the cooling effect of the radiator.

 

Can anyone of you confirm this theory? (Or is it more than just a theory?)

 

Regards,

 

Menno

[Don Elliott]

The bypass hose is there to allow the engine to heat up more rapidly on a cold winter day. Once the coolant in the engine is hot, winter or summer, the bellows on the original thermostat expands and the sleeve moves back with the bellows and is supposed to block the flow of coolant through the bypass hose. I have one of these original thermostats and I have blocked the bypass flow with a brass plumbers pipe plug where I drilled a 4mm hole through the plug to allow all the air to rise out the system when I'm filling it with coolant. In effect I have only about 5% flow when the engine is cold and maybe less when it's hot. I don't mind because I only drive my TR3A in the summer when I don't need a rapid warm-up as in the winter. If the outlet is different for a TR4 housing, I can't see it making any difference because the engines are the same for the TR3 as for the TR4.

[Menno van Rij]

Today I had the chance to compare a TR2 and a TR4 thermostat housing. I noticed that there are only a few visual differences (apart from the electric temp sensor on the 4).

 

- The 2 bolts holding the front and back part of the housing together are on the 2's housing opposite of each other, where on the 4's housing they are a little 'off centre'

- The sensor house on the 2 is located in a 90 degree angle, the 4's sensor house is a bit more positioned backwards.

- The inside of the exit tube to the bypass hose has a round shape on a 2, on a 4's exit tube there are two flat spots. But I think that it has to do with the manufacturer (?)

 

Anyway, I think that it's all a rumour about the inside of the exit tube being square and that Don is right with his observation and solution.

 

I'll keep you posted!

 

Menno