Overflow tank = empty
 

So, I replaced my OEM radiator w/ an aluminum about a month ago after the plastic portion of the upper radiator cracked. At the time of the replacement, my overflow tank was 100% full. I've been checking the filler cap since then and it's been fine (now wish I was checking the overflow too).

Fast forward to this morning…startup the car, roll down the driveway and my add coolant light comes on. Check out the lvl on the filler cap and I don't visibly see any coolant. Looked under the car and there are no signs of a leak, so I added a cup or 2 of coolant and went to work (2-3 miles away).

Just before lunch I decided to check the coolant lvl and it was the same as earlier this morning. Took a glance at the overflow tank and it's COMPLETELY empty, sigh. So now I guess I need to figure out what happened to all my coolant :)

Any advice on where to start? Oh, and does it sound like a blown coolant seal? :'(

have you ever done the air bleeding procedure after you installed the radiator?

what is throwing me off is that it has been fine for a month.. maybe your coolant seal is going bad, that's a possibility too, how many miles on the engine?

Good catch, ya...I followed the burping guide from robrobinette.com (http://www.robrobinette.com/flush.htm) until all the air bubbles were gone and coolant lvl was consistant.

Engine is original and has around 56k miles on it. Haven't replaced the AST yet. That was next on my list actually since it's starting to look a little 'green'.

I've filled up the overflow tank to full, refilled the coolant neck, and stuck some cardboard underneath the car for the evening to see if there's any coolant leaking out the bottom of the car.

Would a defective AST cause something like this to occur :Wconfused

This would happen to me once upon a time. The tube that fed my overflow tank had come out of its bung and was just flopping around. It would allow coolant out but when the engine cooled, because it was unsubmerged, it would just suck air back in. I thought I was losing my motor but I would just feed it and feed it. Once I found the loose tube it never happened again. I never had any visible leaks either. You may want to check into the line that runs to the overflow and make sure it's not squished and air tight.

..dave

The only reason for the recovery tank to deplete itself is that air was pushed into the tank and coolant was drawn back in without the tank being replinished. There must have been more air than fluid and it eventually pushed air out and air back in for you to have a low coolant level in the filler neck area. The minimum level is to ensure enough coolant in the recovery tank to allow the coolant not to over flow when expanding in the system but still have enough in there so as to not pull air in while drawing coolant back into the system, sometimes with air in the cooling system it push's more coolant than air which forcs extra coolant out of the recovery tank (an actual overflow) then when it cools it pull coolant back in but doesn't get all the air out of the system. Do this afew times and you could wind up depleting you recovery tank and still not purge all the air.