My 1991 Accord has about 200K miles and is starting to develope some problems that really concern me.

First, coolant is leaking somewhere but I can't find it. It's not dripping onto the ground or venting somewhere under the hood. There is not any coolant in the oil. But after driving about 30 miles, roughly 1 quart of coolant must be added.

The car is having other problems that are likely related to the missing coolant. When first started, it runs very roughly. It will sputter and stumble for about 250 feet and then seems to run fine. On the road, it appears to run normally. After the engine is warmed up, the idle is very low (around 200rpm) and the engine will stall if allowed to idle.

I suspect that coolant is getting into the combustion chambers. Is this even possible? If so, does it mean the head gasket has failed? There are no obvious external signs that something is wrong.

Can anybody suggest trouble spots that I should be looking for?