Yesterday, I ran my boat on flushers just to turn it over and run some carb cleaner through it. The gauges looked normal until the thermostat opened. Then the water temp gauge dropped from around 140 to 100. There was plenty of water coming out the exhausts. If I throttled up a bit, the gauge came up and then dropped off slowly again. I shut her down to take the flame arrestor off for the carb cleaner and when I started it again, the guage came up to 140 and stayed there. Thoughts on what would cause this?

I have seen my guages act funny on the hose. Not sure why it does it sometimes and not others. All I can think of is that the preasure at the hose changes from the town. I have done exactly what you are and had it work fine then shut down and have it mess up then later fire it off again and have it be fine again. I would put it in the water and see what happens.

Jon

the tap water is real cold ......the engine wont run very warm at first... after it warms the water in the block it should maintain the 140-160 temp of the the thermostat

Dyno, this is Houston None of the water around here is very cold. Anyway, it warmed up to the point of opening the thermostat, and then the temp dropped. My friend is guessing something electrical with the sensor maybe.
I will definitely keep an eye on it when I next get her in the water and see if does anything different.
Is it worth pulling apart the thermostat?

Stats an easy quick job if it has'nt been changed in a while it cant hurt.....

Jana, if you think it may be electrical then start by checking the connection at the sender itself. Then you can check the connection at the gauge.
I personally would just wait till you get it in the water and see if its acting funny there. My scarab acted weid on the hose as well. jumped around from 130-180 while running but never went above 150 while in the lake........

Before I would start checking anything, I would run it IN the water. Readings running off a hose are not accurate unless you run it for a long time and still vary from actual running conditions.

You may have just had some sand sticking the thermostat open.