tsmysak1

This is what I deduced from the search.

Coolant is showing up in the reservoir and not being drawn back into the engine. The engine has just started to need the filler volume topped off when the engine is cool. Is this an AST cap gone bad? I haven't really seen any signs of a combustion leak.

Thanks.

BobfisH

sounds like it! check around the water pump for leaks too

charliegt

Yeah, I had the same problem and it turned out to be the cap on the filler neck. Just replace them all and save yourself some headache, or do one at a time if you want to try and save money.

-Charlie

DaveW

ANY leak in the line from the AST to the overflow tank will cause your symptoms (coolant stays in the overflow tank, and the engine coolant recedes), as air will be drawn back instead of coolant. This, of course, as mentioned above, includes a bad peripheral seal on the AST cap.

The AST cap is easier to replace than to find a leak in the coolant return hose, so that's what to do first.

Retserof

iTrader: (1)

Sometimes the coolant return hose is loose at the AST nipple, allowing air instead of coolant from the overflow tank to be sucked in when the engine cools. I added a spring hose clamp to mine. Other times it is the AST cap or a collapsing return hose.

RX7 RAGE

iTrader: (22)

I have this same symptom and I've already replaced both caps with new oem ones. So the only thing it could be is the line from the ast to the overflow or my water seals could be toast?

tsmysak1

Yeah, water seals..... huh.... I think this is always the first thing that comes up because it is so darn scary...but, there would be some other symptoms too. There should be some water in the exhaust, which I can find none. There should be some indication in the coolant of combustion gas...which I can find none. I am not considering that right now because it just started all the sudden. There is always a flow out of the engine when it gets warm, so somehow air is coming back in rather than water. Should be simple....er.... uh.... maybe not on this car...

The AST circuit diagram should be in the manual ..right?