One of the most famous mechanics on YouTube has shared a simple warning sign that could help them avoid making a serious engine problem even worse.

Scotty Kilmer has worked as a mechanic for more than 55 years and regularly posts videos to his YouTube channel in which he shares tips to help viewers save money and avoid damaging their car.

In a recent video, Scotty urged all drivers to make a 30-second for a sign that their engine's head gasket has blown, warning that it can be seriously expensive to repair.

He explained: "Today I'm going to show you how you can tell if your car's head gasket is blown. Now, head gasket jobs are very expensive. It's not the valve cover gasket here on top, it's right in the middle when the head goes on the block - very expensive.

"When the engine's cold, take off the radiator cap and look inside. Then, start the cold engine and if you see bubbles coming out, the head gasket has blown. If the coolant looks all foamy like a milkshake, the head gasket has blown."

The head gasket builds compression within the engine by sealing the combustion chamber and prevening coolant and oil from leaking or mixing.

If the gasket fails, drivers will likely find that the engine overheats at a much faster rate and, if it goes unchecked, could also lead to other components getting seriously damaged.

According to Checkatrade, getting a replacement head gasket fitted to an engine typically costs £700, with some drivers having to shell out a staggering £1,850 for some high-end cars.

Later in the video, Scotty also highlighted that vehicles with a blown head gasket could also experience white smoke when the engine is idling.

He added: "If you see a bunch of white smoke coming out from the tailpipe, it means that coolant is getting into the exhaust system, and it's certainly not supposed to do that."

Exhaust smoke typically turns white when the head gasket fails due to coolant being burnt by the engine.

In addition to regularly checking engine components for signs of failure, drivers can avoid the costly repair bill by keeping their coolant system in check.

By regularly checking the level of coolant under the bonnet, drivers will be able to avoid problems caused by an overheating car.

Motorists should also routinely check any rubber hoses that relate to the coolant system for signs of cracks and perishing, which could create leaks, limiting the amount of coolant entering the radiator, and be mindful of their engine temperature on long journeys.