Winter Driving 5 :: At Sub-Zero Temps

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Dec. 22, 2005

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articles by Tim Winker.

Part 5

Physics 101 at Sub-Zero Temps

The TV weather forecasters love doing science experiments when temperatures drop to extreme cold. Unfortunately, your car is experiencing some of the same trials as the fluids get thicker, and in the case of some fluids like diesel fuel, may even turn into Jell-O. Here are a few more things you can do to ensure that your personal mode of transport remains reliable when it gets really cold.

Oil

Most vehicle manufacturers recommend a lighter viscosity engine oil for winter use. Check your owners manual for specifics on your vehicle. As temperatures drop, the engine oil becomes thicker, sort of like molasses or honey. A thinner viscosity oil like 5W30 will flow quicker through the engine's oil passages than a summer weight oil.

When you start your engine first thing on a sub-zero morning, be aware that the oil will be flowing slowly through the oil galleys. It can be compared to trying to push a milk shake through a straw. Let the engine idle a few seconds before you give it any gas, and even then tap the pedal lightly to rev the engine a few hundred more rpm. The worst thing you can do is rev the engine hard when it is very cold as oil has probably not reached all the moving parts. The result is rapid internal engine wear and very expensive repair bills.

Thermostat

One item left out of last weeks column on the cooling system was the thermostat. Most engine thermostats operate at about 180 degrees F. Check to see if there is a higher temperature thermostat available for winter use, usually about 195 degrees. The higher temp thermostat will provide warmer air into the vehicle interior.

Sometimes, however, it is just too damn cold for the cooling/heating system to reach a reasonable operating temperature. In that case it's time to cover up some of the opening in front of the radiator. You may notice large diesel trucks with padded covers over the grills to block some of the frigid air from entering the radiator.

A simple fix is a chunk of corrugated cardboard placed in front of the radiator. Do not completely block the airflow, but cover about half of the radiator fins. Cut holes in the cardboard for more even airflow through the radiator.

Tires

Have you ever noticed that when you heat something in a bag or container in the microwave, it expands when it is hot, but shrinks again as it cools? The same thing happens in tires; as the temperature drops, the air contracts. A tire filled to 30 psi on a 70 degree day will drop to below 20 psi when the temp hits 0. Tires are also more likely to lose air through leakage at very low temperatures, particularly around the valve stem and between the rim and tire. That's why it is important to check the tire pressures regularly. Tires will wear out faster when under inflated, and the fuel consumption goes up as the engine works harder to compensate for the added drag.

Tire rubber gets harder as the temp gets colder. Performance tires can get as hard as hockey pucks as they are meant to operate at very high temperatures. All-season tires are pretty good as far as flexibility in the cold, but for optimum use in cold and snow, nothing beats a modern snow tire. The combination of deep tread and rubber that remains flexible to extremely cold temperatures is good insurance to safe winter driving.

Brakes

Brake fluid is "hydroscopic" which means it absorbs moisture from the air. After a few years, the brake fluid's boiling point drops and the freezing point rises due to the water content that has been absorbed. Ice can build up in the lines, wheel cylinders or calipers and the brakes will not function. Some years ago I worked in a shop in St. Paul and whenever the temp dropped below zero, there would be several cars brought into the shop with a complaint of "no brakes" despite there being plenty of pedal pressure. A simple bleeding of the brakes and flushing out all of the old fluid cured the problem. During the brake bleeding process, little ice chunks would be spit out of the bleeder screw.

Battery

Batteries do not like cold temperatures. Just when you need more cranking power to offset thicker engine lubricating fluids, the battery provides fewer electrons to do the job. That's why it's important to look at Cold Cranking Amps (CCA) when purchasing a new battery. The higher the CCA, the more reliable your battery will be when the thermometer hits sub-zero.

Make sure the battery connections are tight and that there is no corrosion growing at the battery posts. Corrosion occurs from a poor connection between the battery post and the cable connector, and a poor connection causes less flow of electrons from the battery. Remove the connectors, clean with a wire brush or steel wool, then tighten them onto the battery posts. A smear of petroleum jelly will help to protect against further corrosion.

While most batteries these days are labeled "maintenance free", you can usually pry off a cap over the cells to inspect the electrolyte level. Many batteries are replaced prematurely because the electrolyte level has dropped, and all it would take is to top off the cells with water. Distilled water is recommended, but in a battery that is already several years old, plain tap water will work just fine.

If your battery is sufficient to start the car at zero, but not up to the task on nights when the thermometer hits 20 below, consider taking it inside overnight to keep it warm. All it usually takes is a few minutes to remove the battery cables and the hold-down straps.

If you have a battery charger, connect it to the battery overnight. Keep it on the lowest setting, just enough to keep the battery active which will also keep it warm.

One other option is to add a battery blanket which is like a heating pad that wraps around the battery. It plugs into a 110v circuit, just like a block heater.

Tim Winker is a freelance automotive writer who lives west of Twig. He has competed in ice races and winter rallies since the 1970s, and in endurance rallies such as One Lap of America, the Alcan Rally and Targa Newfoundland.