Why Tesla Motors Inc. Stock Heated Up

Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Tesla Motors got a jolt today, finishing up 16% after management bumped up its guidance for the fourth quarter of 2013.

So what: The maker of high-end electric cars said that sales in the final quarter of last year were "the highest in company history by a significant margin," as it sold and delivered nearly 6,900 vehicles, beating its own prior guidance by 20%. The company also said that the two key drivers of the increased demand were "the superlative safety of the Model S and great performance under extremely cold conditions."

Now what: Shares of Tesla continued to gain after hours, climbing an additional 3% on enthusiasm for increased sales. The carmaker's shares soared through most of 2013, but hit a speed bump on concerns about engine fires. Those seem to have been assuaged, though, as weeks ago the German vehicle safety regulatory authority approved the Model S, and CEO Elon Musk has been vigilant in his defense of the car's safety, taking every public opportunity to take critics to task. While Tesla continues to knock sales projections out of the park, there is still a strong argument that the stock is overvalued. At a forward P/E of 108, there are enormous expectations baked in. Musk intends for the carmaker to be a transformational company, and investors will need him to pull that off for the stock to move significantly higher.