Hey all. I have an 86 240 sedan. Recently, I've been losing coolant (half of overflow tank gone after 2 weeks.) There's probably 12000 miles on the water pump, and barely any play in the pully. The temp gauges stays nominal after warm-up.
The funny part is, there are no leaks on the ground, and there is also a smell of coolant in my engine compartment. My friend told me it smells like burned coolant. So what should I look for? Could it be the head gasket or something simpler? I'm pretty knowledgable regarding automobile maintenence, but I could use a hand on this one.

Another note. The car has ~140,000 miles on it and we've had it since 1989, so we know that it has been well kept.

Thanks
Martin