Motor Oil May Not Freeze, But Low Temperatures Can Still Cause Problems

Motor oil does not freeze solid like water. Instead, it thickens, and this somewhat solidified state affects what's called a motor oil's pour point. In this regard, the pour point refers to the lowest temperature the oil can endure before it becomes thick enough to resist flowing. When oil becomes too thick or overly viscous to flow, bad things can happen to your engine, and the oil won't reach vital parts in time to provide lubrication upon turning the key or pushing the start button.

It's not just the engine that struggles when running on cold, thickened oil. The battery and the starter are also under strain during cold starts, and your car's fuel economy will suffer due to the longer warm-up sessions required to heat the oil. Industry experts agree that a majority of engine wear most likely occurs during cold starts, and there are reasons for that.

As if thickened oil is not bad enough, your engine also has to deal with gravity that pulls the oil back down to the sump, leaving internal parts unprotected. Engines run on a richer air/fuel mixture when cold, and that tends to wash away the oil on the cylinder walls and leads to damaging friction. Combine thickened oil that takes its sweet time to flow with cold cylinders and piston rings, and it's no wonder that frequent oil changes are your car's best weapon against the potentially damaging and expensive consequences of driving in cold weather.

The pour point range will ultimately depend on the type of motor oil. In general, it falls somewhere between -4 degrees and -58 degrees Fahrenheit, but some oils can withstand chilly temperatures better than others. Conventional motor oil, although great for classic cars and vintage engines, will start thickening at -5 degrees to 15 degrees Fahrenheit. Synthetic-blend oils fare better and will begin thickening at -25 degrees to 0 degrees Fahrenheit, while full-synthetic motor oil will start to resist flowing at -40 degrees to -60 degrees Fahrenheit, making it the best option when the mercury drops and further highlighting the differences between semi-synthetic and full-synthetic oil blends.

However, the pour point also suffers as the oil ages and gathers contaminants. What this means is that even the best synthetic motor oils will eventually degrade through time and heat cycles. That's why you should always check the engine oil before the temperature drops and add oil or change it before cold weather freezes everything in sight. 

As for when to change the oil and how to choose the right blend, your owner's manual will give you the answers. For reference, idling for long periods and driving in frigid climates fall under severe driving conditions and will most likely require more frequent oil changes and servicing. As for deciphering motor oil grades, 0W or 5W oil flows better in the cold than 10W or 15W oil, so it's best to stay within the manufacturer's recommended oil grades when the weather turns icy.