I've searched but found nothing directly about my problem. The add coolant light (and buzzer) is coming on within seconds of cranking. I've added coolant to the overflow tank in the fender with the engine hot and with it cold. I've filled the filler neck above the thermostat with the air separator valve closed and it didn't take much to fill up, but with the valve on the air separator tank open it takes a lot, but never fills. Instead, it runs out the expansion tank overflow! A couple of days ago the thermostat housing cap was leaking so I replaced it with a 16 lb, non-Mazda from an auto parts store. It doesn't leak anymore.

Sometimes, when I add water to the thermostat housing with the air sep tank valve open, the water will come out the air sep tank cap valve, other times it will overflow from the overflow tank! I can't figure it out.

Everything else seems OK, no white smoke, idle is OK, power is normal, no bubbles in thermostat housing filler neck with cap off. I'm stumped.

Could a thermostat that is sticking intermittently cause this weird behavior? I'm not driving much, just easy testing, until I figure this out. The water pump is maybe 8-9 months old. I did it myself last winter when I put in the Fluidyne radiator. Also put in new Mazda OEM thermostat at that time. All was well until recently. First noticed it when I saw a puddle under passenger side in front when returning to car after it was parked at work all day and it got worse over about 2-3 days until the "Add Coolant" light and buzzer started.

Once, after I knew the cooling system was full, it was buzzing and I "got on it" and it quit... for about 15 minutes.

Anybody have any ideas?

Thanks

 

If you have the cap for the ast off when you're pouring coolant into the filler neck, it will come out of the ast, because it is lower. Have you tried burping your cooling system? Have you had the system pressure tested? If ot, then that would be the next logical step.

 

this is not a reply, but a question, how hard was it to put in your fluidyne radiator? What does your temp. gauge read?

 

Are you sure you have the hoses from the AST hooked up correctly? Or maybe your AST is mounted too low. You shouldn't be getting coolant going into the overflow before the AST is full. In my car the AST is slightly below the filler neck (themostat housing), so that fills up first, but the AST and filler neck should be essentially connected and at the same level. The overflow, on the other hand, is completely seperated from the rest of the cooling system under normal circumstances. You only get coolant going into the overflow when the car gets warm and the coolant starts expanding. So, when cold, the two sides shouldn't affect each other.

 

The hose at the top of the AST should go to the overflow. The hose at the bottom of the AST goes down to the radiator.

If you fill the thermostat housing slowly enough with the AST cap off, you might get coolant spilling over the lower edge of the AST filler neck, through the hose to the overflow, and overflowing. I don't think this sounds so strange. It's downhill.

You need to fill the AST, cap it, then fill the filler neck.

Have you replaced your cap on the AST? Have you checked the Negative Pressure Valve on the AST cap? If it's stuck, you can't suck the coolant back into the cooling system from the overflow, and it will spill over.

If the AST cap is ok, I'd pressurize your coolant system and look for leaks. A leak will make you lose coolant pressure, and the system won't suck all the coolant back from the overflow.

 

use plain mazda cap (no spring) on filler neck, and 16 psi cap on ast. top off ast 1st with final bit added slowly from filler neck ... put ast cap on just before overflowing ast. then fill filler neck. expansion tank about 1/2 full cold. as was said, verify hose locations.

if still trouble, pressure test ... lots of places to leak.

 

Check your AST for leaks. Generally they break at the middle hose nipple.

 

Thanks, everyone. I have some checking to do. Good replies. I'll get back to you with results later today after work. I learned some stuff.

I think my AST cap and the thermostat housing filler neck cap are first to get replaced. The hoses are relatively new (replaced same time as the new radiator / water pump last fall / winter) so hopefully replacing the caps will do it.

xstacy7 - putting in the Fluidyne wasn't really difficult but it took several hours because I had never been in that part of the car before and I was replacing my water pump at the same time. I followed the directions in the shop manual, the thick green one, and all went well. As far as temp gauge reading... I don't have an aftermarket water temp gauge yet, it's next on the list, but the stock gauge reads "normal" if you consider normal to be just below horizontal when warm.

 

RotaryiPaq, did you find the problem? What was it?

 

Did you check the sensor mine just went out. the sensor for the 3rd gen is $50 but the 2nd gen one is $12 the only difference is the connection. Just splice it in

 

which sensor was it? the one under the coolant filler neck?