Re: Why no thermostats in some outboards?
My opinion: For years engines were made with 18kv magneto generated open ckt voltage to fire the plugs and no stats. Some didn't even have a shifting device so that you could start in N. The tower was based upon a design of the '50's, i.e. the 6 cyl 60 hp which grew into the 150 hp before the V6 comes out....a new design....with a stat, pair to be exact. I don't remember ever having a stat on a small hp engine, including an 85 4 cyl Merc I bought in the '80's. I had a 4.5 hp and a 7.5 hp of '70's vintage with no stat.
As time progressed OEMs were looking for ways to improve their product and beat the competition. In 1971 I bought an OMC V4 125 hp. which had a stat, but I ran against Merc 125 hp red band towers with no stat. They had 40kv Thunderbolt ignition.....don't remember what I had. As I saw it, Merc learned, from it's testing at Lake X in Florida, that a stat is just a liability in salt water making for more scale in the water chambers (salt deposits increasing with higher temps) and something to fail. So they went with the high voltage CD ignition.
With new designs came stats and the high voltage and things just got better. For the record, the only engine that I ever lost was due to a stuck shut stat with no overtemp horn on a '75 Rude 70 hp triple. My current boat, Merc powered, on my first outing, I discovered that I had a stuck shut stat. but I had a warning horn and saved my engine.
Soooo, like Silvertip said, designer's choice. Trying to better the product to beat the competition.
Kinda rough but my general idea.
Mark
