This week, the ratings of three auto parts stocks on Portfolio Grader are down. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, Modine Manufacturing Company (MOD) falls to a D (“sell”), worse than last week’s grade of C (“hold”). Modine Manufacturing specializes in thermal management systems and components, bringing heating and cooling technology and solutions to diversified global markets. In Portfolio Grader’s specific subcategories of Earnings Growth, Earnings Momentum and Earnings Surprise, MOD also gets an F. Shares of the stock are being traded at a very rapid pace, up 399.2% from the week prior. For more information, get Portfolio Grader’s complete analysis of MOD stock.

Dorman Products, Inc. (DORM) is having a tough week. The company’s rating falls from a C to a D. Dorman Products supplies automotive replacement parts, fasteners, and service line products primarily for the automotive aftermarket. As of Feb. 3, 2015, 15.2% of outstanding Dorman Products, Inc. shares were held short. To get an in-depth look at DORM, get Portfolio Grader’s complete analysis of DORM stock.

The rating of Tenneco (TEN) slips from a C to a D. Tenneco designs, manufactures, and markets emission control and ride control products and systems for the automotive original equipment market and the aftermarket. For more information, get Portfolio Grader’s complete analysis of TEN stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.