Nope. You want the engine up to operating temp. Oil thins with heat; what oil to use is partially based on what temp the crankcase will be operating at, hence old engines like my 1976 Mercruiser 888 (302) calling out three different weights depending on water temps (as back then, good multiweight oils didn't exist yet). Even with multiweight oils, they still have temperature-dependent viscosity (just not as extreme as a straight grade oil).
Also, increased temperature helps with efficiency (increased reactivity of combustion)... and if you have a carb with an electric-only choke, you may have running issues as well due to the electric choke assuming normal warmup behavior. This is largely why cars typically run much hotter T-stats than boats; if a boat could safely run hotter, they'd be set up in such a way.
So yes, you want a 140 T-stat in there for actual running. The only time I'd omit a T-stat was in a pinch (stuck T-stat overheating things) or if trying to flush the cooling system (which is more of an automotive-closed loop thing to clean old antifreeze and other junk out).