Re: why not to run without tstats on bubblebacks
Reel, if you ask older wrenches on the Island, you should be able to get a better feel for how well this works/doesn't work. Some wrenches remove them from older V4s, because they know the engines won't be maintained often. No thermostat is better than a stuck thermostat. Those timy twin thermostats on the 1978+ V4s are particularly prone to sticking in salt water use.<br /><br />Personal experience: Before I knew anything about this issue, I ran a 1989 88SPL without thermostats for a couple years, something like 240 gallons of gas/year, without the compression budging a bit from excellent values. I have taken in two V4s with missing thermostats, both had excellent compression. Both were off Whaler Montauks, owned by what is likely the best high-end sailboat rigging outfit on LI Sound. <br /><br />The original reason for thermostats was to control engine temp, in order to sufficiently warm the intake air/fuel mixture before combustion (reference Ricardo or Obert's Internal Combustion Engines).<br /><br />This is the reason for intake manifold heat risers in car engines. Gasoline doesn't burn well until it is in the vapor state. Some additional vaporization takes place due to heat increase during the compression. Ideally, one wants all the fuel to have just reached vapor state when the flame front hits it. Any additional heating, beyond the liquid-vapor phase change, just expands the mixture and cuts power. Car manufacturers actually go to some trouble to get the intake manifold working so that it delivers about the right amount of heat. This is a low-throttle opening driveability and fuel economy issue. At higher throttle openings, the mixture speeds are waaaay up compared to idle, and everything is vaporized.<br /><br />The reason for choking a motor, when it's cold, is that a smaller fraction of the fuel passes into vapor at low temps, so you have to provide more fuel. The unburned fuel goes out the tailpipe. <br /><br />Race head porters leave the intake passages bumpy to keep the air/fuel mixed, so that the fuel doesn't drop out of the airstream. They polish the exhaust passages to lower flow restriction, because fuel mixture is not longer an issue.<br /><br />Merc inline motors had this goofy arrangement where the intake reed valves were actually wrapped around the crank. The twisted path kept the fuel in suspension better, and vaporized more, so that they idled OK even without a thermostat. In their 1950s/60s ads, Merc claimed the ability to run without a thermostat was an advantage of their designs. Merc ran completely without them until I think the V6 days of the 1980s.<br /><br />A novice taking the powerhead off an old salty bubbleback is likely to have trouble - may just ruin any chance to go fishing that summer. I can tell you that thermostat-less V4s get plenty hot when running [particulary pushing a 19' GradyWhite
]. Once warmed up, I don't believe there's much, if any, increase in wear due to the slight difference in temperature. In particular, I don't think the piston crown temperature has much at all to do with block temp - being more a function of ring fit and piston fit, assuming mixture and timing are equal. It is true that NOx emmissions are higher with cold cylinder walls (at least in a automobile 4stroke).<br /><br />DHadley & others have forgotten more about outboards than I may ever know. If they'll say they've taken apart scads of thermostat-less motors, and they were all coked up, I'll certainly believe them. It is not obvious to me, otherwise, that cold walls would lead to coking, or warmer walls avoid it - in fact I'd suspect the opposite. Further, it's not like any healthy motor gets hot enough inside to burn the deposits off.<br /><br />I have a guy where we go in the summer, I think he's the kid of one of the lobstermen, who just hammers his cold V6 off the mooring every day on the way to work. It's a new motor, so I'm sure it has thermostats, but he's doing more cold start damage to that motor than any themostat-less running would do. <br /><br />I have never sold an OMC without new thermostats. Clearly the motor idles better, runs more efficiently with them, and lasts longer. But I don't think running without them is the kiss of death - nothing even vaguely like running with gummed up lean carbs, or an old impeller.
