Ttalk Tech

Modern Thermostat Installation

The original TD thermostat is an excellent device that should last a long time.  However, time marches on and it doesn't last forever.  An OEM replacement is very hard to find and, if you can find one, the price is frightening.  The obvious solution is to install a modern thermostat.  This requires the modification of the thermostat housing so as to accommodate the new thermostat.  A number of different modifications have been devised.  This page is about the system that I'm using in Lazarus.  I honestly can't remember where I obtained this one.  It was probably from either Abingdon Spares, or Blair Engle.  If you look at the images below you'll see that the inside of the housing has been machined out up to just past the bypass slot.  This has been machined to a diameter of 50.3mm.  The 'spiderweb' above the bypass slot has been removed.  The clever ingredient of this system is the brass sleeve that is used to locate and hold the new thermostat in place. All of the images below are taken from the bottom of the housing:

(Images are thumbnails)

Machined housing:

Brass sleeve (note rectangular notch to uncover bypass port):

Compression slot in sleeve:

Thermostat dropped in:

Sleeve installed:

Bypass slot aligned with bypass opening:

View through bypass:

It may be necessary to hunt up a thermostat will fit in the machined housing.  You'll find that 50 mm diameter thermostats are standard items.  The 75C one that I have in at the moment says 'MotoRad' on it.  I also have one that says 'WaxStat' on it.  BTW, there is a 'toggle pin' in the one that I'm using.  It makes filling the system much easier if the air can get out.

Some folks tend to block off the bypass port or install a restrictor.  I don't do either.  I have an Arnolt heater installed using the bypass adapter and I have a valve in the line that I can control from my seat.  It makes it easy to emulate the OEM thermostat gate on the bypass.


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