Managing engine lubricants in cold climates

To the layman, it would seem that the thicker an oil is, the better. The primary role of an engine lubricant is to provide a protective film between moving parts, and the thicker that film is, the more robust it must be.

Which is true, but only up to a point. In fact, as lubricant and engine technologies advance, oil is getting thinner. Early multigrades were relatively high-viscosity 20W-50s, and now figures as low as 5W-30 are commonplace. 

The first thing to understand is what the numbers actually mean. The two numbers measure different properties, at different temperatures. The second, higher, number indicates the viscosity of the oil at working temperature: + 100 C. The first, lower, number is used to measure different properties: the resistance presented by the oil to rotational ‘cold-cranking’ and pumping movements, which simulates an engine start at a low temperature: – 18 C. The letter ‘W’, incidentally, stands for ‘Winter’ and not for ‘weight’ as some would have you believe.

So, the lower the first number, the colder the oil temperature at which the engine will still start. Using a 5W-30 such as the Texaco Delo 400 range, will provide superior cold starting qualities to a 20W-50. And the advantages don’t stop there. Engine wear is maximised at cold start, irrespective of ambient temperatures, because it takes time for the lubricant to reach such far-flung components as the valvetrain. The more ‘pumpable’ the oil, the quicker it will reach and protect these vulnerable surfaces.

But what happens at the other extreme, when an engine is working hard in a high ambient temperature?  All other things being equal, the oil will thin out and start to leak past piston rings and valve seals. Ultimately, the protective film may break down, resulting in metal-to-metal contact and component failure.

And this is where the magic starts. Engine manufacturers design components which, in the case of plain bearings, for instance, may have coatings that reduce friction in their own right, or, to use piston rings as an example, are specifically shaped to retain an even film of low-viscosity oil.

But most important of all is the oil blend. Low-viscosity lubricants are typically made from a synthetic base oil, enhanced by viscosity modifiers, anti-wear agents and performance additives to produce a lubricant that can withstand high temperatures and shear stresses while still flowing easily. And this is where quality and durability found in Texaco Delo low viscosity products really counts.