Doesnt the D1 thermo open sooner due to the thermostat being in the engine and right next to the sensor rather than outboard like the D2?

I havent hooked a scanner to my D1 in a while, but when I first put a 180 stat in it, I remember it was about 186-188 in early summer rush hour.

 

I would agree that with thermostat in the block you will get quicker response. Since I have an American made thermostat, it starts to open at the stamped temp. So my truck is quite happy at a constant 178, just opening a wee bit then closing back. If I stop and idle the temp goes up, but I don't get to 15 degrees past start to open (wide open). In the summer I do because radiator is compromised. When I first started on the forum my temps were going up to 227, etc.


I may be stupid, but I believe the engine is happy with a constant temperature, not 30 degree swings, and that under 200 is good. The oil is happy 180 ish and above, but when really hot it will thin out. The oem D2 stat is rated to start to open at 179 and fully open at 205. But that might be in a teapot. With the plumbing between the block and the thermostat, some difference of 5 -10 degrees is going to be built in. So having the Rover lower temp stat will bring you back to a more reasonable spot. If you look at the stat for the older Rovers, the manual shows testing it for operation, 82C, which is darn close to 180F, wide open. All the emissions control madness has forced engineers to run things hotter to get that last little 1/4 of a percent of performance to satisfy the "law of the land." I would point out that few law makers turn a wrench.

If you take a D2, with Dexmud in a good percentage of the radiator, and add some clog to a few of the metering holes in the thermsotat, it is no wonder things are warmer than you would like. But Rover "hides" that with the temp gauge computations by the ECU. So the unsuspecting owner thinks all is well until ... (pix for general idea)

 

You are making me blush. Wow, that's a big difference. Amazing you still get good efficiency from it with that differential.

EDIT: Just read your last post. Looks like the efficiency does suffer in the Summer...

 

I run the motorad 180. Average cruising temp is 187. When its 80 or so outside and Im climbing the mile or so long hill on my way home I hit 198, then sometimes 201 if I have to sit at the light at the top of said hill. More common max temp is 194. Although Im pretty sure im still on the original radiator. And i havent tested it for hot spots so i have no idea how efficient it is.