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During my recent exercise to replace the cam followers and camshaft on my TR3a I decided to take the opportunity to fit the original bellows type thermostat that I have been carrying around in the boot for a couple of years. Up until now I have been using a modern type thermostat with a coin with a 6mm hole blocking the bypass outlet. The bellows one is marked 82 deg whereas the other one is stamped 89 deg.

 

I assumed that this lower actuation temperature would mean that the car would run a bit cooler but this has proved not to be the case. The needle ends up pretty much in the same place on the dial, just to the left of centre unless I am stationary for any length of time in which case it rises quite quickly and the fan kicks in. Would this be because the bellows is less effective at cutting off the flow through the bypass than my crude bodge with a coin?

 

Rgds Ian

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I think there is an element of error in terms of the accuracy of the thermostats.

 

My Stag at a lower temp on the dial when I put in a new stat in which was notionally higher than the one I removed.

 

Of course temp gauges have a wide margin of error but it's unlikely to have changed significantly during a short period of time.

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I would take it out and check it in a pan of water with a thermometer to see what its actually doing as it seems this type of thermostat does go "Off" after all these years. I have just had one rejected by my engine builder as U/S despite being NOS.and never fitted.

Stuart.

Edited by stuart
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Hi Stuart,

 

I did check it was working by immersing in a pan of boiling water before I installed it, although I admit didn't check the temperature at which it was operating.

 

This one was NOS as well.

 

I'll give it a few more days and if it becomes a problem it will be back to my 'bodge'. (I still have the coin, which incidentally was not a 10p piece it was a US 25 cents, and the jubilee clip)

 

Rgds Ian

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Tech tip:

If you want to measure (boiling) water temperature but do not have a glass thermometer that goes to 100 degrees C, you can use a cheap IR thermometer, keep it perpendicular to the water, to avoid your measurement gets influenced by the cooking pan metal which may be hotter or colder, and is refected in the water mirror.

Waldi

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I had a similar problem with an original thermostat, by checking them in boiling water with a new stat they both opened at the same temp, what was different was the amount they opened, the new stat opened 25% further. Fitting the new stat reduced my temp quite significantly, the fan now rarely cuts in and the temp gauge is just where you want to see it rather than the hot side of the middle.

Paul

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