I just got an 86 NA the other day I came outside to find water under the car. It came from the overflow on the rad. Just to be safe I bought some Prestone stop leak crap. Now it runns really hot and the low coolant buzzer sounds until it warms up enough to cycle water through the engine. It also smokes really bad if I gas it while it is cold, but only for a minute. Any ideas? Should I just flush the cooling system? There are no leaks that I see.

 

replace your thermostat with a mazda t-stat. At least that's what fixed my similar problem.



And I'm guessing you still have a little air in your system. I never could get all mine out unless I remove the bleeder screw where the upper rad hose meets the rad. Fill until fluid comes out that holes, then screw it back in and keep filling.

 

Another method to removing all the air from the cooling system is to remove the hose that comes out of the rear plate and attaches to the thermowax assembly, assuming of course that your throttle body is still equipped with it. Being the highest point in the cooling system air seems to reside there. Once a steady stream of water/coolant comes from that tube the cooling system should be air bubble free.