I have my 181 mercruiser with a th350 transmission in my trike. I'm not planning on running a thermostat. How do I determine the size of radiator that is needed to cool the motor? The motor is stock. Can a motorcycle radiator work, or is it to small? Does the inlet and outlet of the radiator need to be similar in size to the motors water pump and thermostat housing size. I'm using a Goldwing front end, the inlet and outlet on it is 1". Can I reduce down to that or is that to much of a restriction? Is there a web site that can give me information such as volume of water that the motor contains and or the volume of water that flows through the motor when running?
Do some research, find a car , truck that uses a 3.0 L engine, ( there's a lot !) and then research the size of radiators used, stop at a radiator shop and ask!
May I ask why? Having a cheap, simple device to hold the engine at proper operating temperature all the time (except the first warm up minutes) seems preferable over having an engine that's colder or hotter than ideal almost all the time. About coolant passage sizes, the fully open thermostat is normally the smallest passage in the system (and actually used as an intentional exit restriction to keep coolant pressure up a bit higher inside the engine, increasing the boiling point). With sensible length lines etc. I would think it should work as long as everything else is a fair bit larger than the thermostat opening.
I'm probably wrong, but my thought on the no thermostat, since I won't need a heater, I won't need to worry about water temperature, as long as it doesn't over heat, I'm good. I wasn't thinking about keeping the motor temperature constant, for best performance.
Well, that depends on how strict interpretation of "good" you mean. Burning gas mostly creates CO2 and water, for everyday street use you want the entire engine (including the oil) hot enough to keep that water as steam rather than condensating and ending up in the oil. You want the oil hot enough to boil off any fuel or water that ends up in it too. I'm sure you've noticed the difference in how a cold and a hot engine runs, the choke has some ability to compensate for the different fuel amount required when very cold but not enough to make it run well, just enough to make sure it starts even on a cold morning (unlike modern fuel injections that can make engines run very well at any temperature, masking the fact that the engine isn't really happy when cold). Without thermostat you may have an engine varying between perhaps 100F and 212F (depending on weather, driving style, radiator capacity and so on), that's a very large difference and your carb adjustments will only be ideal at one temperature - which one do you pick? In a race engine where you want maximum performance you aim for a bit lower temp, there the working conditions are stable enough to work well anyway, and you change the oil often enough so water/fuel contamination can't become a problem and raw fuel washing oil off the cold cylinder walls isn't really an issue at high rpm anyway. On the street you want a stable, relatively high temperature to make the engine last long and run well all the time, both on a cold spring morning cruising to work on the small low speed roads and a hot summer afternoon using full throttle going down the highway. So, can it work well enough to "be good" without a thermostat? Absolutely! Can it work better and last longer with a thermostat? Oh, yes!
If you don't want to run a thermostat, the shell of the one you took out of it or shell of one that fits usually slows the coolant flow down enough so that heat transfers from engine to coolant and from radiator to air . It's still a bit slow to warm u compared to one with a thermostat but you never worry about a stuck thermostat. The restricted radiator openings should handle that part though. The Goldwing radiator is probably the same capacity as A Vega or Pontiac Astre radiator that is about 12x20=3/4 core area.
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