I understand that both the LR grey t-stat and the Motorad are 180 degrees, but am I correct that the LR gray has a soft spring that opens easier, and therefore more reactive. I am not sure what the Motorad has in regard to stiffness in the spring, and how evenly or steady it opens?

Anybody know more about the spring in the Motorad t-stat?

 

I believe the soft spring refers to the one that allows the bypass disc to "descend" and open flow to allow earlier heater operation. The larger spring, when the main section opens, forces the bypass disc back up to closed off. So it is more of a better operation during warm up when using the heater.

 

I need to get an old one of those to cut open. From what I can see in the pic it (the guts) looks like the thermostat in my 300tdi.

 

And like the stats on my Mercedes 300TE and 300CE Cab. And some Fords. The only wrinkle is the small metering holes in the bypass disc to provide flow of coolant to warm up the main chamber to make main stat open.

Cedric Whistlebriches in Rover Engineering decided on a stat that opened at 180F, and was fully open at 204F, despite the fact that the unit would be remote, have some cooling from the air flow around it, and be a long way from the 82C fully open on a Defender (page from Rave on a 1994 is attached). It seems to me looking at the older manuals (on the same engine basically) that we used to be fully open at 180F. Now on a D2 we are starting to open at 180F, fully open at 204, plus throw in the extra for loss of heat transmitting through the plumbing, and loss of some plumbing and the stat body being blast cooled by local air flow. And a computer controlled gauge that hides the changes in coolant temp from the owner. So the proud owner considers his Rover a rock, it never overheats; until one day.... after hours of slow roasting over hickory coals.

Those bypass disk metering holes, should they become clogged, would impact when the main stat gets warm enough to open, or open further.

Add some Dexcool sludge to the radiator, and temps will move higher.

I guess the remote stat is one way to make the heat come on faster for comfort in the cabin. But I bet a lot of D2 owners would trade some of that comfort for longer HG life.

Rant over.

 

That is exactly the trade I made.

I get a little less heat because the spring is softer in the grey thermo, thus reducing flow to the heater core during idle operation, and the reduced coolant temps also reduce the heater temps. The trade off is that the engine temps are lower, the coolant pressure is lower (by reducing the vapourpressure in the system) and overall engine seems happier. Hopefully get a little extra time out of the head gasket.

 

And the heater core has less pressure and flow at idle, and we know how fun there are to change!

 

This is another view from Lucky 8.

2003 Discovery 131K with high miles service complete

 

during 3 years, using the thermostat original(OEM) y siempre trabajando en stop and go entre 203 a 208 y highway bajaba a 199.
cambie a motorad 439-180 y trabajo en stop and go 201 a 208 y en highway 200. lo use por una semana.
cambie a pel500110 TD5 original(OEM) y trabajo en stop and go 199 a 203 y en highway bajo a 195 y es el q uso ahora. es el mas estable y mantiene las temperaturas mas Baja sin afectar la mezcla de combustion.
y vivo en el tropico...
I used destilade water and MOTUL orange.

 

Que parte del trópico?

 

I have the one from BPUtah and it is as advertised. I ordered another one from Atlantic British to have on hand as a spare. They advertise it as the Pel but it is not the grey thermostat. It is the white Motorad. I have not yet called them about it. Not what i wanted. I have had two Motorads that were defective in the past. One the o-ring was not seated properly and the other the thermostat would never open.