How do you tell if a 1989 Mercury Cougar needs a water pump or thermostat?

Answer 1

when a thermostat fails, it stops all water flow. the engine heats up but the radiator stays cold. start car, watch temp needle on dash. when engine temp reading is in mid-range, shut off car, go feel radiator with hand. if very warm or hot, thermosat probably okay. if cool or room-temp to the touch, thermostat is failed shut. My way: drain the coolant, remove the thermostat housing, pull out the thermostat and look at it. is it shut? if it is, it is bad, and replace it. put good one in, carefully clean thermostat housing with soap, water, scrape off scale with razor blade, NOT CUTTING INTO ALUMINIM sealing surface, apply RTV red to a thoroughly degreased and scraped surface on the engine, and re-install thermostat housing. re-tighten fasteners 24-hours later to take up slack in RTV as it sets.

when a water pump fails, it begins to leak coolant out of a small weep-hole on the pump body, to show that its seal has failed. It then starts to make a squealing or chirring noise, and then, when it seizes, it breaks the drive belt and makes a horrible, unmistakable noise like the roof of the car being torn off. If the pump turns quietly and normally, it works just fine.

when the coolant is low due to a small leak, the system is not always refilled correctly, and can look like it is not cooling after it was just filled (but incorrectly, with lots of trapped air still in the system).

If your cooling system was ever over-heated, fully and seriously, the thermostat was probably damaged. It should be replaced ($10) to avoid the fun and excitement of blowing the head gasket ($550).