Don't be a dipstick when it comes to oil
Short trips are toughest on your engine

Motor oil is the lifeblood of your engine.

As a lubricant, it reduces the friction and subsequent heat and wear created when parts rub together. As a coolant, it circulates through the engine and the oil pan hanging beneath the vehicle. Oil also acts to gather tiny abrasive particles and deposit them in the filter and absorb the corrosive chemicals produced by the combustion process.

Changing oil at recommended intervals is critical. Failure to do so not only can cause extensive engine damage, it can void the warranty.

One of the most common problems facing motorists is when to change oil. Most manufacturers have two sets of oil-change intervals, recommending you change it more frequently if you subject your vehicle to severe use. But most people are surprised to learn that mundane, slow trip to the post office or occasional Sunday drive puts you in the extreme or severe use category.

Driving short distances and leaving the vehicle unused for periods of time actually causes more harm to the engine than the driver who revs the heck out of it and commutes several hundred kilometres a day. Cold starts and short runs generate moisture and corrosive acids. If the oil does not reach high-enough temperatures to cause the moisture and acids to evaporate, they remain in the engine.

Conventional motor oil is a byproduct of the distillation process used in refining crude oil. The crude is a thick viscous fluid; as it is heated, it is separated into various stocks -- the thickest for roofing tar and asphalt, the thinnest for gasoline and other fuels and the gaseous byproduct for propane. In the middle of the spectrum are lubricating oils, to which each oil company adds its special blend of additives.

Synthetic oils have a very uniform molecular structure allowing then to perform consistently in the harshest conditions. Refined oil contains a variety of products of varying molecular structure, which break down at different times. Synthetic oils are more apt to leave a protective film on moving parts after sitting for a longer time, making the subsequent initial startup easier on those parts.

Thermal breakdown is the worst enemy of refined oil. It creates sludge, a tar-like substance that can damage the engine. Sludge is commonly caused by leaving too long an interval between oil changes, and in cars that experience "severe" conditions because of frequent short trips.

Turbochargers can also be a factor as they greatly increase the heat stress on an engine and its oil.

Synthetic oils not only begin lubricating at lower temperatures than petroleum-based oil, they can withstand much higher temperatures. Synthetics have better shear capability, more "cling" and less viscosity change over time. They are less prone to coking and creating varnish.

If synthetic oils are that much better, why not use them even if not required by the manufacturer of your vehicle? Cost.

Because they are more expensive to produce, synthetic oil costs considerably more than petroleum-based oil. If you change oil more frequently because of high mileage or severe conditions -- dusty roads, short trips et cetera -- refined oil may be a better bet economically.

Most manufacturers of high-performance vehicles and those with turbochargers or superchargers recommend synthetic oil to provide added protection against heat and other severe conditions. Synthetic oil is also a good bet for those who take extra care with their vehicle, plan to keep it a long time or store it for lengthy periods.

But, if you change your oil at the intervals suggested for the type of driving you do, good-quality, petroleum-based oil is more than adequate. This also applies to the vast number of drivers in fleet, company or leased vehicles with no interest in the long-term health of the vehicle.