Burning smell

We have a 2002 Sequoia 4X2 with 70,000 miles on it. The last couple of nights, my wife has pulled it into the garage after a 35 mile drive home from work. Each night, I have smelled a burning smell when next to the vehicle. The same smell you sense when your vehicle is overheating. I've checked the radiator, and it is full.

Any ideas what this could be, or what it could be signalling?

Thanks!