Sure, engine operating temperature has a direct impact on emissions and economy, so there is always that delicate balancing act between NOx, HC, and mpg. The knobs are different from engine to engine. CARB does not include "cooling system" in the guidelines, so you're free to mess with thermostat, radiator, fans, hoses, whatever. About the only stock thing on my XR4Ti is the water pump.... there is nothing left of the original cooling system. They don't care.

I don't pretend to understand mechanical engineering, but I think we can agree the VM 2.8s oddball thermostat goes great with their oddball camifold which goes great with the insane timing & serpentine belt drives. IME, it's a typical Italian approach to "engineering." I've owned enough Italian cars at this point to simply accept that if there's a tried and trued solution to a problem, you won't find it on an Italian car.

PZKW108; you are bang-on correct! I am ABSOLUTELY certain that the O.E. CRD engine thermostat assembly was made non-serviceable for the following reasons...

1) ... so you have to pay through the nose for one through the stealership because the typically the only way to get a replacement thermostat assembly is though... the stealership.

2) ... so you can not replace the thermostat valve inside with one of a different operating temperature to make your engine run properly, (read that as efficiently, reliably, and with more power). In the eyes of the all-powerful Environmental Protection Agency, peons like vehicle owners must be prevented from making their vehicles run correctly so that their ridiculous emissions standards are maintained. They can then have bragging rights to the World's strictest pollution standards and therefore justify the E.P.A. administration's 6 and 7 figure salaries. Too bad their entire ideology regarding pollution control is counter-productive; what the H-E-double hockey sticks point is it to lower NOx if you are going to burn upwards of 30% more fuel to do it? HYPOCRITES!!

FORTUNATELY, one of the great things about the HDS Model 001 is that it uses the Hemi engine thermostat... This valve is available in three opening temperatures; 203, 190, and 180 degrees Fahrenheit. If there EVER comes a time that the E.P.A. mandates measuring engine temperatures, a CRD owner that has a Model 001 thermostat in it can simply install a 180 degree thermostat valve during the testing period.