I’m here to tell you that’s a bad idea.
Over the years, there have been a few folks who have pushed for FIAT replacement thermostats that open at lower temperatures. The factory specified a 190-195 degree (Fahrenheit) open, but some aftermarket producers have gone as low as 175 degrees.
What are the actual benefits of going lower?
Put your engineering hat on with me, and let’s talk applied science. If you consider the internal combustion engine as an air pump operated by thermal expansion, *more* block heat is *more* power and efficiency. — Every joule of energy sent out to the atmosphere as heat (through the radiator) is a joule of combustion energy lost. —
For proof-of-concept, look into the experiments in the 80s and 90s with ceramic engine blocks. They ran hot and achieved better efficiency (power), but nobody could make one last for obvious reasons. The temperature limitation we have come to expect of our motors is a function of the materials necessary (metals and gaskets) to build long-lasting motors.
Modern manufacturers regularly wait until 230 degrees (or so) before even turning cooling fans on. Many run up around 260 before there’s any significant longevity concerns. That’s mostly a function of superior metallurgy and higher pressure cooling systems.
Running motors cooler than designed (the FIAT DOHC included) is bad practice, with almost exclusively negative consequences. It puts manufactured clearances out-of-specification, because those specifications were set *at design temperature* for component materials that expand at differing rates. Which means that engine components tend to wear faster when too cold. Also, in more extreme cases, if engine oil is not allowed to reach a normal temperature, the condensation that occurs inside a crankcase (as a function of heat cycling) can create a significant concentration of water. Obviously, this has numerous detrimental effects.
Most people who swap in low temp thermostats do so because their cooling systems have other underlying issues. I would always recommend dealing with the problem over a potentially dangerous band-aid. You can see my post here on how to correctly burp the cooling system of a FIAT 124 Spider, to make sure you aren’t chasing a simple problem.
Hope this is helpful,