Electric car maker Tesla Motors Inc. reported a wider third-quarter loss and trimmed its forecast for deliveries this year, citing delays to a planned factory overhaul.

The Palo Alto, Calif., auto maker reported a loss of $74.6 million, compared with a $38.5 million loss a year ago. It also lowered its forecast for full-year deliveries of its Model S sedans by 2,000 vehicles to about 33,000.

Tesla...