Cooler thermostats are a mistake often proposed by those that can think only in general terms rather than understand engineering.

IC engines run most efficiently at higher tempereatures and your computer controls expect the thermostat MB installed.

Anything else is a mistake and hurts rather than helps.

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Kent Christensen
Albuquerque
'07 GL320CDI, '10 CL550. '01 Porsche Boxster
Two BMW motorcycles