I don't know where my sending units are. For the Mercury engines I've
had I always got a nice shop manual for the specific engine from
Mercury. I haven't had a chance to get one for these Johnsons yet. I
do see a wire coming out of the power head just left of the thermostat
that I was guessing might be it.

I was thinking that even with the thermostat completely removed that
the pee hole should still have a stream of some kind - so I was
thinking my water pump was suspect. Are you saying that with the
thermostat completely out the pressure is reduced enough so that the
pee hole may just dribble (with no stream) and my water pump may still
be good?

If so, maybe I should just replace the thermostat on the cold one and
see if it "warms up?" If it does I could then do a "hand test" to see
if they are both pretty close to the same heat range? And I could
also see if their guages start reading close to the same heat range?

Unfortunately these thermostats are weird plastic ones that I've never
seen before and I don't think I would be able to see anything if I
boiled them. And more unfortunate is I won't be back home until
Friday evening to continue working on this.

I really appreciate your help. I haven't really even got a chance to
try this boat out because of this problem and I'm really dying to. I
did schedule an appointment in 2 weeks with the mechanic. But the
sooner I can get it worked out the sooner I can try out the boat

Thanks,
Eldon

You should have metal OMC# 396987 143 degree thermostats in those
engines. This is a recirculating system, and at low displacement speeds
(the water pump - not the vessel) you will have a drop in pressure as
your "warm" water is wasted out the exhaust relief and exhaust hub
without the thermostat in place. It may even be low when the pump
reaches centrifugal speeds.

Put known good thermostats in and check your water jacket temp. I think
you will be alright.

Rob