WINTER driving and short trips can combine to cause engine problems such as oil leaks or apparent oil consumption.
A "short trip" can be defined as any time your vehicle is started without letting your engine's oil reach full operating temperature. Depending on outside temperatures, it may take only a few minutes or up to half an hour before your engine oil is fully warmed up. Most private vehicles driven in the city would fall into the short-trip category.
Water is the culprit in your engine's problems. Each time you start your vehicle, air inside the engine is warmed up quickly and water vapour condenses on the inside of the cold metal engine block. These water droplets dribble down the inside of the engine into the oil pan. A similar effect can be seen whenever you take a cold glass jar from the refrigerator and place it on a table. Water vapour condenses on the surface of the jar and runs down onto the table.
While water is essential to the engine's cooling system, it can be harmful inside the engine crankcase. If the engine oil reaches full operating temperature, the water inside the crankcase evaporates and is pulled into the intake manifold by the engine's crankcase ventilation system. Then it passes through the combustion chambers and out the exhaust system. Part of the exhaust fog we see during cold weather is water vapour.
When the engine oil never reaches operating temperature, the water collects in the bottom of the oil pan and low spots in the crankcase ventilation system. I've seen several short-trip vehicles with more than a litre of water sitting in the bottom of the oil pan. This isn't seen on the engine dipstick because the oil floats to the top.
A long trip on the highway will evaporate this water, so it might seem that your engine is suddenly using a lot of oil. In reality, your engine has been using a little oil for a long period of time (a normal condition), but the level on the dipstick has remained constant because water has replaced it.
Water that collects in low spots in the engine's crankcase ventilation system can freeze when the vehicle is turned off. The next time you start your vehicle, the ventilation system can't work and air pressure that normally builds up inside the crankcase cannot be released.
The result is oil forced out past engine seals and gaskets. Enough oil can be forced out that engine damage can occur in less than 100 kilometres of highway driving due to a shortage of oil. Replacing the seals and gaskets may repair any current oil leak, but it will not cure your problem.
There are ways to prevent engine damage. One way is to change your engine oil more frequently during cold weather. Changing oil every 5,000 km may seem excessive, but it also removes any water.
Another precaution is to have your engine's crankcase ventilation system checked. Replace the positive crankcase ventilation PCV valve as indicated in the maintenance recommendations in the owners manual and check all the hoses for low spots where water could sit and freeze. A mis-routed hose can cause problems, but even hoses that are routed correctly can sag and create a low spot. Sometimes a hose needs to be repositioned slightly. If the system is plugged, water vapour and fumes cannot be pulled from the engine crankcase.
Finally, the most economical method of preventing engine trouble is to change your driving habits. Combine several short trips into one longer trip. This allows the engine's oil to warm up fully and evaporates any water in the oil. It can also save you a bundle on fuel costs because the vehicle has to be warmed up only once.
Jim Kerr is an experienced mechanic, instructor of automotive technology, freelance journalist and member of the Automobile Journalists' Association of Canada.