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Originally Posted by infernosg
After the first "event" I filled up the radiator and managed to drive 2.5 hours home averaging 70 mi/hr with no overheating, but the buzzer would come on occasionally during tighter turns and lower speed driving. Once I got home and the car cooled off I topped off the radiator and bled the system the best I could. At this point the radiator was completely full and the overflow bottle was at the full level as well. I was able to drive to and from work (only 8 miles) with no issues on Monday and I let the car sit most of the day yesterday. Yesterday afternoon, after driving more recklessly than I'd like on the street, I came home and revved the engine in neutral in the driveway. No buzzer while doing all this so I turned it off and let it sit for about 30 minutes. Before starting it up again I noticed the overflow bottle was now ~1" above the "full" mark. I made it to the end of the driveway when the buzzer came on. Since it was still fully warmed up I just pulled back up and turned it off for good. The buzzer did go off as soon as I started to move back up the driveway.
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The 1" extra coolant in the overflow bottle 30 minutes after a hot shutdown sounds about normal. When you shut down the engine the radiator cap allows pressurized/expanding coolant to flow into the overflow tank, raising its level. When the system cools down enough, the resulting vacuum should suck the coolant back into the radiator, leaving the overflow bottle around the full mark.
Quote:
Originally Posted by infernosg
What has me most worried is the constant bubbling I'm getting in the overflow bottle. To ensure it wasn't be caused by engine vibrations I removed the overflow cap and tube and placed it in a cup of clear water. With the car fully warmed up there was a constant stream of tiny bubbles coming out of the pickup tube. Only once did a moderately large amount of coolant get burped into the cup. After that it was back to the bubbles.
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If air is getting into the system, from either a leaky radiator cap or anywhere else in the system, it could explain the bubbles you're seeing. And it would explain the added difficulty in getting the system fully "burped" and keeping the buzzer quiet.
Quote:
Originally Posted by infernosg
Pressure testing is my next step before throwing new parts at it (rad. cap, thermostat, water pump). The plan is to swing by an auto parts store after work to see if they have anything I can rent.
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If you're going to throw parts at it, I'd suggest getting a new Mazda radiator cap & thermostat regardless, especially if you don't know what's in there now. Don't bother buying a Stant or aftermarket thermostat - for some reason the ones the make for rotaries are crap.
Quote:
Originally Posted by infernosg
The one thing I can't seem to explain is the original overheating event. IIRC, the cooling system holds like 2 gallons of water and I know I didn't add nearly that much after it overheated. The fact the buzzer came on just as the temperature gauge started to rise also has me stumped considering it has come on many times since that and the temperature gauge hasn't moved.
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If your system is all stock, the cooling system is barely sufficient for track duty - it has very little excess cooling capacity, and a just a little bit of pump cavitation due to the prolonged high revs can easily boil things over. The buzzer sensor needs to be immersed in coolant at all times to keep it quiet - just one air bubble under it and BUZZZZZZZZZ. The temperature of the coolant has no effect on the buzzer - it's a level sensor.