Engine warm-up and oil viscosity

What actually happens inside an engine when it's cold and the oil's viscosity is several times higher than its calculated working value? Recall your school physics course and the conclusion is clear: if the oil film is thicker than the clearance, friction increases, which leads to a drop in power and a rise in temperature. This is precisely the "secret" that engine designers build in: they calculate clearances for the engine's working temperatures (which for most engines is considered to be the 100-150 °C range), deliberately forcing the engine to run under increased load while it warms up.

It's precisely the inflated viscosity of cold oil that helps the engine warm up faster. And that's exactly why automakers strongly advise against putting load on the engine before it's fully warmed up. And it's exactly for this reason that specialists claim that every single cold-weather warm-up takes roughly 300-500 kilometres off a new engine's total service life (not to be confused with the oil's service life — it doesn't affect the service interval nearly as much).

It should be noted that over time the engine's internal surfaces gradually wear, clearances widen, and correspondingly the degree to which the elevated viscosity of cold oil affects wear diminishes.