Originally Posted by rob8888
Does the NAPA thermostat that happened to fit open at the same temperature as the OEM thermostat? Most marine thermostats for small diesels open at 160F, but automotive thermostats usually open at 180F - 210F, which is hotter than the factory usually specifies for a marine engine. Many marine thermostats are made from stainless steel because they're designed to be used in both fresh-water and raw-water cooled engines, while automotive thermostats don't need to be stainless because they're always used in an antifreeze coolant mix. When Westerbeke orders stainless steel thermostats with a lower temperature than standard automotive parts they can't order a couple of million like an automobile manufacturer can; they probably only need a couple of hundred, and therefore the manufacturer charges them a lot more to make them.
Yup...both are rated at 160F. A metallurgist might be able to tell the difference in the two...maybe. But to the eye, touch, feel, smell (ok, maybe not), they are identical. My primary concern was fit (size) and temp rating. Dead match...can't beat that.