Johnson 100HP V4 1972 engine had a shorted neutral solenoid. While diagnosing it in the water in somewhat of a frustrated panic, it was in neutral (from forward) and it ran at probably 2000-3000RPM for maybe it seemed up to a minute in neutral and tripped the overheat horn. I realize very stupid... The second the horn started blaring, we shut engine down immediately. I had recently replaced water pump, and I've retested compression and all 4 cylinders are still all around 120PSI +/- 5 PSI, so I'm assuming I escaped major damage. But I was surprised how fast engine overheated in neutral. Engine had been idling for many minutes at regular slow (600-700 RPM or so) and didn't overheat, and it didn't overheat when we were at WOT. I will recheck my impeller and Tstat just to make sure, but does an V4 outboard generate a lot more heat than the cooling system can handle if the motor runs too fast in neutral for such a short time? I verified my heads were 210 degrees right when the horn started going and I shut it down so I know it was definitely overheated.
Before I put it back on the water, I wanted to know if an engine will heat up that fast in the water if it runs too fast in neutral. I know there are lots of reasons why you should never run above 1500RPM in neutral, but is overheating one of them? If so, I just won't ever let that happen again, but if the engine should still not overheat that quickly even at such a fast speed in neutral, I'll do a more thorough check of the cooling system.
Before I put it back on the water, I wanted to know if an engine will heat up that fast in the water if it runs too fast in neutral. I know there are lots of reasons why you should never run above 1500RPM in neutral, but is overheating one of them? If so, I just won't ever let that happen again, but if the engine should still not overheat that quickly even at such a fast speed in neutral, I'll do a more thorough check of the cooling system.