Warming up the engine – the facts

Some drivers will let their car warm up before heading off for the day - find out if it's really necessary.

Jason Fenske from Engineering Explained answers the question simply; no it is not.

The modern vehicle, and those manufactured in the last 25 years, is fitted with a fuel injector system. The fuel injector system will push more fuel through the cylinders and pistons when a car is cold to create a richer air-fuel mixture and allow for complete combustion.

Carburetor fitted engines cannot do this, and if driven before the engine is sufficiently warmed, the car will stall or cut out.

Where it is not necessary for fuel injected engines to be warmed up before driving, the car should be left idling for 15-30 seconds then driven lightly to ensure the engine oil is heated up to recommended operating temperature to avoid wearing out the engine.

Gasoline, or fuel, is a solvent and as such can corrode or breakdown oil. Oil can act as a protective layer for the pistons and cylinders, and when extra gasoline is pushed through these cylinders without the oil being at temperature, it may result in unnecessary wear on the engines parts.

These forced rich air-fuel mixtures can result in dilution of oil, where fuel will pass through the pistons and mix in with the oil itself. This can promote wear in the engine, and cause the oil to oxidise and breakdown quicker, forcing you to change the oil more frequently.

Having the vehicle idle for a short time won’t put much heat into the engine, but it will allow the oil to circulate and once driven lightly will warm up quickly. This will assist  in preventing premature wear to the pistons and cylinders.

For the science behind it all, watch Jason Feneske’s video on the matter.