Engine Cooling problem
1998 Mazda 626 4 cyl Two Wheel Drive Automatic 170000 miles
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Ive recently changed the transmission in my 1998 Mazda 626 and now i'm having cooling problems. Ive changed the thermostat and replaced one of the fan motors on a radiator fan (it was burned out). I have a small leak in the radiator on the side of the engine where the air intake is. The car will run at normal temperature for 20-30 minutes before it starts over-heating then shoot right up to the red. The water levels have been anywheres from normal to way low when the car overheats. Also, the car has started to idle real low, at about 500 rpms and the car wants to shut off when standing in idle. Any solutions or opinions of what all may need to be changed is much apreciated.

Replace the radiator!!! would be the first thing i would do,if it has a leak,then you may see the car acting funny! I remember this happened to me when i had a chevy nova 1987 model (love the car which was basically a toyota corrolla) but the radiator had a small leak/crack, had to change the whole thing out and it worked fine afterwards! That may be a good start to it!