Marinette Boat Forum

I would like to order a new thermostat for my 1979 Chrysler 440.

I have a PDF scan of an old 440 manual which indicates a 140 deg. thermostat for raw water cooled and 160 deg. for freshwater cooled. My engine is raw water cooled, so I am inclined to order the 140 as the manual indicates. However, a few friends have told me the 140 is "too cold."

Thoughts or opinions? My understanding is that the lower temp for raw water helps to prevent excessive buildup of scale, etc., in the engine block/manifolds. I run my boat in fresh water lakes/rivers only.

I recall 140 for raw water also per the manual for my former 1988 boat. It did not say why the difference was specified but I suspect it's not for the reason you cited

Better stick with the 140. Your motor will run around 150/155 with it.

The reason for the lower T-stat on raw water engines is a lack of pressure in the system (unlike FWC where the radiator cap maintains 7 pounds or so). Water boils at a higher temperature under press, and will BOIL inside the motor during heavy load conditions (and steam is a lousy coolant).

Jeff