Here we are in January, which brings the coldest temperatures of the year to our central and northern states. By cold, I'm talking about temperatures in the 20s and lower. Any temperatures colder than this can impact straight No. 2 diesel fuel.

Normally, this shouldn't be a problem. Fuel marketers are pretty good about blending their diesel products for trouble-free engine operation 10 to 20 degrees colder than normal ambient temperatures for that area.

However, several problems can – and do – arise. Starting point may be driver complaints of power loss. Next point may be engine shutdown and being unable to restart. Both may be diesel fuel related.

Often the problem can be traced back to fuel waxing, which can plug fuel filters. No. 2 diesel has a fairly high paraffin (wax) content, which normally is a good thing. It adds to the fuel's Btu content, which translates to power and fuel economy. However, if untreated chemically or blended with No. 1 diesel, the wax begins to form crystals (cloud point), and these are trapped in the filter, causing power loss by starving the engine. If temps are sub-zero, untreated fuel will gel and totally plug filters, causing engine shutdown.

This is why many fuel systems have fuel heaters in conjunction with filters. These typically are connected to the engine's coolant or cab heater circuit so the hot coolant transfers heat into the filter housing and warms the fuel. This is undesirable in hot weather because it reduces fuel economy.

A straight No. 2 diesel (often referred to as Summer Fuel) is preferred because it gives the best fuel mileage. Its typical cloud point is 18 to 20 degrees, but it can be as high as 40 degrees. No. 1 diesel is mostly kerosene, a first cousin to JP-4 jet fuel. Its cloud point is good to minus 40 degrees. Pour point is the temperature at which the paraffin in the fuel crystallizes and fuel gels to the point where it resists pouring. These temps are typically 10 to 20 degrees below cloud points.

So what's the point of all this? If your fleet fuels from your own bulk storage tanks, make sure you are getting blended fuel (mix of No. 2 and No. 1) during cold-weather months. Know how frequently you "turn" that fuel. I know several fleets that have 40,000-gallon storage, but their fleets have been downsized and part of that 40,000 gallons might last four months. If they tank up in October, chances are that fuel will not be blended for zero-degree temperatures anticipated in January. That's when the trouble begins. It's advisable to turn fuel storage monthly during winter months.

I recall a situation 10 or 12 years ago where a major common carrier fueled its rigs at its Arkansas terminal and then dispatched a dozen of them to Minneapolis. There, a cold spell had dropped temps to near zero. Drivers didn't refuel locally, parked and their rigs wouldn't start. Filters all had to be changed.

Another fleet I know stays with No. 2 diesel year 'round for fuel economy and gives drivers jugs of additive, or directs them to buy local fuel when temperatures are forecasted to drop dramatically.

Another piece of cold-weather advice – and this one is controversial: During cold weather PM services, have shop technicians add a pint of denatured alcohol (the kind you buy at the drug store) to each truck's fuel tank. All tanks pick up small amounts of water, often from condensation. Water settles in tank bottoms, can freeze and can cause big troubles. Denatured alcohol absorbs water and prevents fuel line freeze-ups. It works, I vouch for it.

I should add, however, that engine manufacturers frown on the practice.