Here's the problem. My parents own a 1990 Lumina AVP, and the antifreeze tank is constantly, moderately slowly, emptying. The catch is, there's no puddle under the van, nor is there any antifreeze under the hood spilled or leaked anywhere. Obviously it's going somewhere. Does this stuff evaporate easily if the cap is not on tightly? Could it be that where the tank is put together (the plastic seam) it is coming open and it's leaking there? Any help would be appreciated.

Thanks,
Corey

This has always puzzled me too. I wouldnt worry about it too much unless your rad gets low, or you have overheating problems. I have had the same problem on my 93 Caprice, and on my parents 96 Jimmy. Eventually the tank is empty, or very close to empty, but the rad always seems to be ok. Just check the rad every once in a while and do a little top-up if it is low in there.

On most GM's the manuals specify to have coolant marked the level (cold or hot depending on temp). In essance, they are really just overflow tanks anyways.

Is the engine temp ok? Are you having any overheat probs? What about low coolant lights / alarms? (if equipped for your vehicle). Im guessing it just evaporates.

Just remember to keep an eye on the rad every once in a while and every thing should be ok. :)