It is not widely realised that the thermostat fitted to TA/B/C/D and Y-Types was only supplied as a complete unit with the cast body, there being no means of replacing just the thermostat itself.
We now offer a new design which allows the thermostat unit only to be replaced by removal of a stainless steel circlip.
We stock replacements on part number NB308AA. As the standard thermostats are too large to fit inside the housing these are modified by a special press tool to the correct diameter.
Some owners have found benefits by reducing the flow through the by-pass outlet to a small bleed hole (4.5-5.00mm). We therefore include a stainless removable disc and circlip to provide this option. We recommend removal of this disc unless there appears to be a specific need.