Add Coolant Warning Buzzer
 

I am working on a FC, 1990 , 5 speed. Shortly after I bought it I started getting this alarm, when the level in the res is at normal. So I'm thinking it's a sensor , so I have it diagnosed at Mazda (for $90 , OUCH !) and it revealed the sensor was faulty. So I bought the sensor and installed it myself but the buzzer still continues occaisionally. The FAQs suggest bleeding the radiator, can I get a little more detail on this procedure. This suggests that there is a bubble in the radiator, but I have even removed the radiator cap and filled with the engine running and the heater on, and naturally got some overflow, but I would think that would have taked care of any bubbles. Any ideas ??

Are you sure it's the low coolant buzzer?

Try pulling the sensor on the radiator, with the other fill caps closed and make sure there's water up to the sensor.

You may have a blown coolant seal that's pushing air into the cooling system.

have you tried grounding the tip of the sensor to the frame while the key was on?

Grounding the sensor has no effect.
You have to ground the wire that is on the harness,that GOES to the sensor to make it stop.(sensor wire disconnected.harness wire goes to ground)
NOW,If you do that and there is a buzzer that goes off afterwards then it is NOT the coolant level sensor( you just ruled that out).
That buzzer is also hooked up to the Low oil sensor and I Think Seatbelts.

The warning light that comes on with it says " Add Coolant " There is a warning light for low oil level but it doesn't light up when the buzzer comes on .

It only comes on occasionally. Yesterday it was on all the way to work, today not a peep.

Notice any leaks? There could be a very small leak somewhere along the hoses or the heater connector that is hard to detect.

After you flush the system,and refill with fresh coolant it may take a bit to get the air out.
Look up Burping the coolant system.
I had one car that the only way I could get air out was to put the front end on stands.Start and run,then shut down.(She was a total snot Bag!)

No leaks on the garage floor. Haven't had a warning in two straight days. But, I also haven't done anything to the coolant level since the warning went off on Monday . Strange ?

Maybe the air worked its way up and out.
Keep an eye on your coolant level just to be Safe,Ok?

I would suggest checking the fuses. It might be an electrical problem.

Thanks for your thoughts guys. 3 days , no warning .

A valid point Shftin, but I went through both fuse boxes shortly after I bought it, and replaced two blown fuses

Well, on the fourth day, the buzzer was back on again. After looking at the res, it appeared that the level had gone down. So I refilled the res. and no buzzer today. It could be as "hioctane" said , a small leak, possibly it only leaks when driving ? Still no leaks on garage floor. I'll keep a close eye on the coolant level.

that happend to mine i replaced the cap but when i fiiied it i took my time and keeped slowly filling it while it was running it would fill up then slowly go down 5 or6 times each time i saw real small bubbles till it filled up to the top and stayed there for 5 or so min it has never bussed again each time it fills up give it time to settle

It sounds very familiar with the issue I had before. I would suggest u to pop the hood after a good spirited drive, with the radiator and the res both topped up.

Right after u park the car, take a flashlight and pop the hood and check the thermostat housing first, then check the lower coolant hose from all angles. U should be able to notice bubble sounds or maybe a bit of coolant shooting out somewhere.

It's very likely the bottom of the lower coolant hose or the heater hose that connects to the radiator. Worst case scenario u have a leaking radiator.

First of all, let me thank all of you that have responded, I appreciate you taking the time to reply and give your insights.

Now two days since refilling the res, and no buzzer. Just came back from a "spirited" drive, as hioctane suggests, and found the level in res still the same and all the spots rsantaniello has suggested appear to be completely dry.

I guess at this point I am under the assumption that the original diagnosis from Mazda was correct in that the sensor was bad, and now I am slowly removing the bubbles as rsantaniello suggested.

I will keep posting my observations, thanks again for all your replies.

i can think of a case much worse than that.

A little update ,

Almost a week and not a peep out of it. So it looks like the air has finally worked it's way out. Thanks again for all your help.

One suggestion for anyone else who may have this particular problem, I think that since the design of the fill neck on the radiator is so far offset that it makes it diffucult to get the air out, that it may be beneficial to fill the radiator through the Coolant Level Sensor hole, obviously with the engine cool.

You can bleed the system by taking the radiator cap and allowing the car to idle on occasionally grabbing the upper rad hose and squeeze and also turn the heater on defrost full blast and let it run for bout 15 to 20 mins! That should bleed the system for you!