I have an '87 N/A. I tried searching but found nothing that was close enough to my problem. What's happening is when the car is sitting at idle, the coolant light will come on. When the motor revs up, it turns off. The light will come back on a few seconds after it resumes idling. The water temperature doesn't get hot. I bled the coolant system today, and it stopped for a while. Also, the coolant reservoir will be right at the "full" line when the motor is off. When the car is started, it will quickly overfill. The next thing I'm gonna try is to replace all of the hoses. The thermostat is a thermostat from NAPA. I'm not sure if that means anything. Any other suggestions on what to do or what the problem may be? Could it be the water pump?

 

coolant light comes on when its missing coolant or is not bled properly

I your overflow tank gets full shortly after starting/warming up engine, you have most likely blown coolant seal and your engine is rebuild candidate.

U might check all connections, pressure caps, thermostat etc...

 

"Quickly overfill" could be a major problem.

Start with the easy stuff like a new Mazda OEM thermostat and new radiator cap. Check for slippling belts and the fan clutch.

Make sure that you are running the proper antifreeze/water ratio. Most people miscalculate the ratio because of the volume of coolant in the hoses/engine/core..... when doing so-called garden hose flushes.

 

Eh. Quickly overflow usually means blown coolant seal, though as has been mentioned, check the simple stuff first. If it is a coolant seal, you could get away with a "soft seal" rebuild - pull the engine apart, put new coolant seals in, put it back together. If you have it that far apart, there's no good reason to not replace the apex seals though, since you'll still have two good housings.

As for the coolant light coming on at idle but not higher RPM, this means you're only a little bit low on coolant. As the engine RPM increase, the water pump is spinning faster, and the increased water flow will splash up on the sensor & make it think there's coolant in the engine. The sensor is very touchy, which is a good thing.

-=Russ=-

 

Tried the coolant seal test, and it didn't surge out. I did, however, pay some attention to how to hose to the overflow bottle was routed. It was routed from the radiator to the bottle. The only cap in on the T-stat housing. There is what looks like another nipple where a hose could be attached, but it's plugged. Can that affect anything?