Although it is preferable to apply oil when the engine is cold, adding oil to a hot engine will cause no harm. The metal parts of the car’s engine are not so fragile that adding colder oil to the engine will harm them; the most crucial feature is that the oil is the same as the one currently in the engine, because mixing various viscosities of oil is not recommended, unless in certain circumstances. To actually start using, going to add oil whenever the engine seems cool is commonplace even though it is easier and more efficient to determine the appropriate number, minimizing underfilling or over pressurization to oil.

Silky Terrier Dog Breed Playing Aro... Silky Terrier Dog Breed Playing Around

When the weather gets cooler, especially in the winter, it’s better to warm up the engine first, then let it cool down for no more than 15-20 minutes if the temperature drops below freezing, to allow the oil to settle. The heavily thickened lubricant will be able to restore to its proper fluidity after this preheating.

Following such procedure, the oil level can be properly determined. The newly fresh oil is thus easily combined with the existing oil in the engine to form a homogeneous mass. It is indeed essential to use the same type of oil each time. Nevertheless, you might have to change the oil to a hot engine inside an urgent situation, except for when in the case of emergencies oil pressure warning flashes just on display during travelling. 

This is a typical occurrence, and it raises problems such as what happens if you put cold oil in a hot engine. You saw that the oil level was below the minimal level on the display, or you stopped the vehicle and checked the dipstick and discovered that the oil level was low. Then you got a canister from the trunk and refilled it till you were sure it was safe to drive once more.