89 2.9L ranger. 97, 000 miles. I bought it recently and had a massive leak from the water pump. I had never done any work on a vehicle but decided its time to learn. I did drive about 4-5 miles with almost no rad fluid (by accident) before I noticed the leak - perhaps I fried the temp sending unit? It was negative 10 C that day (14 F), I hope there is no serious engine damage... Replaced water pump (after market prestone), thermostat (180F $8 aftermarket), replaced all hoses. Had to use Heli Coil from pervious owner stripping bolts. 300km on the road with no leaks. Then a drip leak in the rad started, used stop leak and it seems to have worked. Truck runs fine, heater works fine (perhaps a little cooler than normal - but still very warm). The temp gauge moves from cold up to the low end of normal and back to cold again, it does this over and over. What could be the problem? People on another form thought: 1) cheep 180F stat 2) temp sending unit broken. Thanks for any ideas.