Diesel & Biodiesel Vehicles in Cold Weather: 3 Things to Be Aware of

Automobile on Winter Road
Philip and Karen Smith/Stockbyte/Getty Images

Be mindful of these three issues on your diesel before cold weather strikes and you’ll eliminate common diesel cold weather starting problems and at the same time help your diesel provide you with safe, reliable travels throughout the most challenging season of the year.

The Fuel Itself

Cold weather starting problems, sluggish diesel fuel, the necessity to use anti-gel additives . . . You’ve probably heard that the biggest problem with running diesels in cold weather is the tendency of the fuel to gel. No. 2 diesel (the grade recommended for most passenger vehicles) contains some naturally occurring paraffin (wax) and as the temperature drops, this paraffin crystallizes and affects the fluidity of the fuel and may cause hard starting and eventually lead to filter plugging. Unfortunately, this problem is exacerbated when biodiesel enters the equation—biodiesel tends to gel at a slightly higher temperature than diesel.

Luckily these problems are fairly easily solved. Regular diesel fuel is “winterized” or seasonally adjusted at the distributor before it’s delivered to the pumps. Winterizing is done by mixing pump No. 2 diesel with No. 1 diesel, its more refined cousin. Winterizing diesel fuel is done to maintain the cold weather flow characteristics, and the ratios vary depending upon regional distribution. To effectively use biodiesel in cold climates, it must be mixed with winterized diesel in varying percentages, which, once again, are regionally dependent.

Tip: It's a good idea to add diesel fuel cold-weather treatment or an anti-gel additive to ensure that you maintain the low-temperature flow characteristics of the fuel. Available at auto parts stores and department stores, anti-gel treatment may be conveniently kept in your trunk and poured directly into your diesel's fuel tank before filling up.

There is ongoing experimentation and research on the cold-weather treatments for biodiesel blends higher than B20.

Are Your Glow Plugs Happy?

If your vehicle is equipped with glow plugs, they need to be in good working condition, along with the glow plug relay. Glow plugs are small electric heating elements (they look like mini spark plugs that are installed in each cylinder.) They are on a timed circuit and activate for a few seconds just before the engine is started. The colder it gets, the longer those glow plugs need to stay on to pre-heat the combustion chamber for a smooth start.

Tip: If your glow plug light on the dashboard doesn’t light when the ignition is switched on, that’s an indication that you may have a glow plug out—and a noticeable engine stumble will be another big indicator. Even one glow plug out may prevent the vehicle from starting.

Check that Battery

When it’s cold outside, everything is a little more sluggish—the fuel is cold, the engine oil is thick and even your car’s cranky. Will she start? Make sure the battery is in good condition. It needs to hold a good charge to provide adequate cranking amps—a diesel requires upwards of 1,000 cold cranking amps to get that engine running. A stout battery provides the sustained cranking power and duration needed to get the engine running in cold weather.

Tip: Check the label on the battery to see how old it is. Those pop-out dots should indicate the month and year it was installed. The label should indicate the life expectancy; they usually range from 48-72 months. If you suspect your battery is getting near the end of its life cycle, it may be a good idea to replace it before cold weather strikes.

For biodiesel cold weather issues, check out winter Rx for biodiesel, along with several quick fixes to get back on the road again.