Hey GT, is that under 160 at idle also?
Sent with my Fingers
Maybe you need to understand why... This also will cover why I disagree with bypass style thermostats.
When your jet boat motor is at idle, there is little to no block pressure and very low water flow. This lowers the boiling point of water. The higher the pressure, the higher the related boiling point. Having the proper flow will determine the water temperature. That being said, without having the margin of safety of being below 160°F at idle, you run the risk of hot spots (aka, steam pockets) and causing permanent damage to the engine. Basically over heating one or two cylinders (most likely the rear cylinders) and killing parts like valves and pistons.
The reason the motor will cool off while hard under way is the increased water flow through the engine, if set up correctly, the block pressure should go up to about 15 PSI and the temp will typically drop to approximately 15°F up to about 25°F. You can run it warmer, but why? 120°F to 140°F is in my mind perfect.
Bypass thermostats, without the use of a block mounted automotive water pump, cause more problems than they prevent. They work great at WOT, but at idle, can cause these steam pockets to form in the heads and be extremely detrimental. With a block mounted pump, the system works better because the water temperature is more homogeneous.
Another dumb fact is that salt water drops out salts at anything above about 165°F, that means salt can actually block the water passages if left with low flow. Not a real problem in most of our worlds, but betting it could become an issue at say Long Beach Marine Stadium during the races... As an example.
You always hear stories of marine engines "dropping a valve", it is sometimes caused by a very hot cylinder head and causing the valve to stick in the guide until the piston comes up to visit and smacks it right in the face... Not always, but betting 50% of the time. This same issue can cause bent push-rods and broken or pulled head studs...
GT
