We’ve all been there: it’s six in the morning, the windshield is wearing a thick coat of frost, and the air has that bite that makes you regret every life choice that led you out of bed. You turn the key, and instead of a confident roar, your engine gives you a hesitant, groaning crank.

While most of us immediately blame the battery—and often rightfully so—there is a hidden culprit swirling inside your engine blocks that is equally frustrated by the freezing temperatures: your motor oil.