Friday suddenly I see that Engine Temparature needle started to move towards the HOT side pretty fast. I had to stall the car and towed it to a mechanic. All the necessary checks were done by the mechanic and mechanic replaced the Thermostat with some generic product (NOT the Mazda one) and one internal switch. He measured the temparature of the Engine at various places, but, the temparature seem to be not of concern. But, after he replaced the Thermostat the temparture reading on the dash board varies between 60%-75%, which is not good, but better than that it was on Friday. Mechanic himslef is confused on what could be problem.
The needle raises to half within less than 1 minute after the vehicle started after an overnight idle, which is not good.

What could be reason ? what could be the issue.

Inputs and suggestions are really needed.

Thanks
brao

May be the gauge itself. Could be temperature sending unit. You could try an amperage resistance test on it. Is your car really overheating? may be a thermostat that runs hotter than the original.

Had the same problem with my old protege. I changed the thermostat along with the cooling fan. must of the parts were original mazda. if i were you get a quote of mazda parts to try and see what happens. for the time being when at a stop light try putting it in neutral usually cools car down a notch.

the likley explination is a loose or broken impeller on your water pump (replace it). you can still be building pressure with such a condition but not sufficent to fully cool the engine. also the problem will not be externally obvious. $40 and about 2 hours you can fix this and avoid serios engine damage. it is also a good idea to replace the timing belt when you do this.

What you describe (rapid rise in temp on gauge) sounds like a resistance problem. If you like you can replace the new thermostat as well. Try cleaning the engine ground cable first. That should change the temp gauge reading. The temperature sending unit reads resistance and it varies as the temperature rises. The value drops as the temp rises. Haynes manual says start the engine, wait till the gauge shows at least half way up, then remove the wire from the sending unit. If the gauge reading drops, replace the sending unit. If it stays high the wire or gauge have a problem.
I tell everybody to spend the money and buy the service manual for their vehicle. Its almost as good as your own mechanic and a lot cheaper. I have a Haynes, the factory book, and a Haynes computer codes & engine management systems manual.