An engine cold start occurs when the engine is started after having had enough time to cool too close to ambient temperature. Most commonly, a cold start occurs early in the day after a vehicle has sat unused overnight. The reason cold starts require consideration, especially in cold climates, is that as the engine and engine oil cool, the oil becomes more viscous (thicker) and more difficult to pump. Also, in many engines, the engine oil has almost completely drained back into the pan, away from the areas that need lubrication. At cold start, the oil is flowing slower and, for a small amount of time, there is little to no oil flow at the lubrication points in the engine. This can contribute to insufficient lubrication and premature wear. This is not a catastrophic condition, but engine wear is cumulative, so reducing wear at cold start by improving cold lubrication will reduce the rate of accumulated wear in the engine.
There are a couple of good ways to improve lubrication, both at cold start and throughout the entire operating cycle. First use a premium quality engine oil that is of the correct viscosity grade. Higher quality engine oils will typically thicken up less with decreasing oil temperature and thin less with increasing oil temperature. Concerning viscosity grade, often the viscosity grade recommended in the vehicle owner manual and printed on the oil fill cap is best. Vehicles manufactured before 1990 may have a suboptimal viscosity grade recommendation because the lubricant technology 25 years ago is not what it is now. For example, 10W- oils (as in 10W- 30) were extremely common, while 5W- oils (like 5W-30) were not. This is important because cold flow of an engine oil is indicated by the first number of the viscosity grade. The smaller the number, the better the cold flow. Current engine oils today are commonly offered in 5W- and 0W- winter grades that optimize cold flow while maintaining viscosity at operating temperature. So now, any vehicle that had a 10W-30 or 10W-40 viscosity grade recommendation can improve cold flow and cold lubrication by simply switching to 5W-30 or 5W-40, without effecting protection at full operating temperature. Modern, premium lubricants also offer better lubrication and wear protection than value brands.
Second, using a premium quality oil filter can help with cold start lubrication by presenting less flow restriction through better filtration media, and by keeping all of the oil from drain back to the oil pan with an anti-drain back valve. Better filtration media, like 100% synthetic micro-glass offers superior filtration while also reducing flow restriction, compared to common cellulose filtration media. The anti-drain back valve acts as a one-way flow path that prevents oil above the oil filter in the oil circuit from draining back to the oil pan. This keeps the oil circuit “preloaded” with lubricant for the next engine start.