I’d had some suspicions the original thermostat wasn’t working as the engine never really got that hot.

Despite what anyone tells you, running an engine for prolonged periods on the open road, with no thermostat, will markedly shorted the life of the engine. Engines are designed to work most efficiently when they are hot. If the engine is always being cooled, it will never reach operating temperature… unless you’re towing a trailer full of bricks over the Gotthard 😉

90% of engine wear occurs in the first 10 minute of driving.

The original thermostat was indeed caput so I ordered a 75 degree replacement. When it arrived, it was clear it was a totally different shape and wouldn’t fit in the housing. A bit of research found the the oringal “bellows” style thermostat are no longer available and the “modern” items need to have the top housing replaced with an item from a later model Series 2a.

A new top housing was soured from the UK along with another thermostat… this time an 85 degree one. The reason?…. Modern multigrade oil will cope with the additional  heat much better than older single grade oils that would have necessitated a cooler thermostat.

New housing, thermostat and gaskets (one for spares)


Check it fits


and more importantly, the top housing fits over the top (which the old unit didn’t)


Judging by the colour of the new top housing (Duck Egg Blue), it’s of military lineage but as the rest of the water pump and thermostat is matt black, this will need a quick coat of paint.

High temperature paint…


… drys in about an hour 🙂


Double checking everything fits together


Top housing back on the engine, top hose reconnected and coolant fluid refilled

How does a thermostat work?

The bulb of the thermostat is filled with wax. When the wax is solid, the thermostat is closed. As the engine coolant heats the bulb, the wax melts and expands inside and forces the top and bottom of the thermostat to separate allowing water to be pumped around the radiator.


Almost done…

…the observant amongst you will have seen there is one bolt missing on the Otterswitch. It had been bugging me for a long time. I’d attempted to order the correct bolt a few times but always received something totally wrong.

Having tidied up my oily Land Rover nut and bolt collection recently, I was able to empty the jar of oily bolts on the work bench and found the correct sized 🙂

The Otterswitch (on the end of the green cable) now has 3 bolts