pull the cap and take a look. if its low then refill it and add a coolant leak dye to help pinpoint the leak. common areas for leaks are heater core hoses, water pump, hoses. head gasket. check the oil and see if its a milk shake.
hmmmm.... mystery smells with no signs of loss. the last time i had this I had a pin hole in the top of the radiator. it didnt show its ugly head until I replaced the radiator cap ( tested and failed ) I am not saying this is your problem.
Maybe someone else will chime in.
I would pressurize the system and take a look for a little leak.
When the engine is cool, check the center head bolt that goes through the exhaust manifold, on the firewall side. On the first and early second gen cars these break and coolant seeps around the bolt and is evaporated by the exhaust, never showing a leak or a puddle under the car. They can be replaced without removing the heads too.
I agree with Bigdogg, pressurize the system with a tester you can get AutoZone to lend to you - don't exceed the pressure printed on the cap (should be 16lbs). I have the same engine, and I can tell you, there are a lot of hoses in there! If you are up to it and they havn't been done lately, replace all of them! Besides the upper and lower rad. hoses, I believe there are seven 'heater' hoses. Do not try to save money and get some bulk 3/4" hose - it won't work! The hoses are molded into tight bends, and at least one of them has a different i.d. at either end (if I remember correctly, it's the water pump to tee-2). Three or four of them share the same part #. NAPA has them all in stock, I think. If the water pump and/or radiator is/are original, you may want to go ahead and replace them as well.