EspressoConvertible

My 9-3 overheated on the expressway a few weeks ago, when it was in the upper 90s and humid. First I noticed the a/c was getting warmer, then I saw the temp gauge, which was really hot. There was almost no coolant in the tank, I had to get some after I sat for a few mins waiting for the engine to cool. I've never touched the coolant in my BMWs, why would it drink up this much? It's an '04 convertible 2.0t. Thanks

Roto

Any smoke? I'd pull the spark plugs and see if there's signs of coolant there. Also check the oil for signs of coolant in there. If you find it there you've got yourself a blown headgasket. It's also possible that it was dumped into the exhasut through the turbo, but than you'd have a lot of smoke and it's unlikely.

EspressoConvertible

No smoke, no noticeable damage to the car or engine, the engine just got really hot, and I was suddenly low on coolant. Would extreme temperatue and heavy use use up a lot of coolant?
Thanks

Roto

it's closed system, so wherever it went, it wasn't supposed to. You need it checked out.

EspressoConvertible

I'm not sure if you understand quite what I mean. There are no leaks or drips, its pretty dry in there. When I took it to a garage to get it refilled, the mechanic did not mention anything. My question is more of an excessive coolant use than a leak.
Thanks,
EC

Roto

use of coolant IS a leak....internal leak that is...most likely through the headgasket into the cylinders where it is getting burned.

EspressoConvertible

if it happens again I'll have it checked out at once. I haven't noticed anything since I have been driving the BMW lately. Been raining for like two days here, the Saab does not like it .

Roto

oh...one thing to consider....if it overheated it could have simply dumped coolant out of the overflow...could be simply an overheating issue....check if your radiator fan is running if it overheats again...

EspressoConvertible

ok, thanks