Remove the thermostats from the heads and see what happens. Not the sensors
but the actual thermostats. If this cures the problem then chances are one
was partially closed up.
You can either replace them if your in a cold climate or just run without
which is what most do in the south.

--
Tony
my boats and cars at http://t.thomas.home.mchsi.com

-
"mjb920" wrote in message
oups.com...
I have a '97 Pro-Line with a 150 HP Merc that has recently experienced
overheating problems. It idles at about 150F, and gets up to over 180F
at higher speeds before I idle back down. I am guessing it has both a
water pressure and a water temperature alarm, because sometimes the
alarm goes off right away when the motor is started cold, sometimes not
until the temp gets over 180F.

I replaced the impeller, which made no difference. The pee stream seems
hot and not as strong as usual. Is there anything else I can check?

Thanks,
Jim