My Rendezvous overheated suddenly Monday Morning.

My Rendezvous overheated suddenly Monday morning and I stopped, checked things over, and waited for the blowers to go off. There was a funny smell like a combination of something burnt and soy sauce. I started it again and was able to make it to work. On the way back, it almost overheated, but I turned the vehicle off before it could and waited a second then turned it back on. The rest of the night it did not overheat though it did inch that way every once in a while. The way to work has more stop-and-go traffic while the way back had a mix of speeds.

The next day, my car took about five minutes to get up to normal heat. It ran at normal temperature for about three more and then overheated twice with me repeating my previous procedure each time and I decided to go back home, with it overheating twice more. I sped up to 45 and then down to 35 the rest of the way home and it did not overheat the rest of the way home, though it did begin inching back up once. This second time I noticed that until about half way home after the last overheating,

I've been told that it could be a problem with the thermostat being stuck closed but was then told that when thermostats fail they fail in the open position. A mechanic did the chemical and sniffer test on it and concluded by the presence of hydro carbons in the coolant that it was a leaking head gasket. Another heard the symptoms and agreed. The only problem is that there has been no outpouring of white smoke.

What's going on? I would appreciate any help you can give me.

Thank you,

Clifford Stumme