The temp gauge in the Universal M4-30 in my 1974 O'Day 32' CC has never worked since I got the boat 3 years ago. I don't know if it ever worked after the boat was repowered from an Atomic 4 to the Universal diesel, at the yard where I keep my boat. I have a service manual and parts list, as well as a wiring diagram that differs from what is on my boat, but I traced the wire from the sender to the gauge, and that seems correct. I read a voltage getting to the gauge from the sender, but am not sure if it is in the correct range. I also checked the gauge with an ohmmeter, and it was not open, and the meter caused the gauge to deflect part scale. There was also +12 Vdc and ground connected to the gauge. I obtained a new sender, the one listed in my parts list for my engine (p/n 299066, if I recall correctly; I don't have the docs here at home, they're on the boat), and it was very different from the one I replaced. The previous one was about half the length and smaller in diameter, and threaded into an adapter. The new one threaded into the thermostat housing in the same tapped hole without and adapter. It seemed long enough that I was afraid it would damage the thermostat. The gauge now deflects down from zero when the key is turned on. There is also a a switch threaded into the thermostat housing that is an overtemp switch that should sound the Sonalert if it closes. After about a half hour of running, I get what sounded like the prop shaft galling (but wasn't when I checked the engine compartment), an irregular whine that is quiet and a completely frequency than that made by the Sonalert. I was thinking dirty DC from alternator brushes that might be on their way out. Any thoughts from anyone out there on either of these puzzlers?