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If your car has a ton of miles racked up on the odometer, then you have probably wondered about doing an engine flush. You may have even been offered the service by your local mechanic or oil change facility. But is an engine flush really necessary to keep your car running for a long time?

What is an engine flush?

A Jiffy Lube mechanic changes the oil on a customer's car. | Getty Images
A Jiffy Lube mechanic changes the oil on a customer’s car. | Getty Images

An engine flush is when a non-solvent flush chemical is added to a car’s engine oil in order to break up any carbon deposits and other gunk in the engine. The gunk and sludge get built up over time in engines that have not had routine oil changes, have a lot of miles, or otherwise have not been cared for.

To perform an engine flush, an additive is simply poured into the engine, and then the engine is left to idle for about 15 minutes. When the time is up, the mechanic will drain the engine’s oil (which is now mixed with the additive), change the oil filter, and then fill the engine back up with fresh oil.

As you can imagine, some of the proposed benefits of an engine flush are that the carbon deposits and other build-up will be flushed away with the dirty oil, which will keep the engine running in its top form.

An engine flush might not be the best idea

While the concept of flushing a car’s engine might sound like a great idea, in most cases, it’s not. According to master mechanics like Scotty Kilmer – also a well-known YouTuber – and the BMW Doctor, it’s not a good idea to run an engine oil flush on any engine, especially those with variable valve timing. The reason being is that the additive loosens up the dirt and grime inside the engine, which can clog up the various oil galleys and passages located within the engine when the oil flush is performed.

On engines with variable valve timing, there are also solenoids and filters that can collect all of the crud as well, which will in turn end up harming the engine later on. Also, if the engine has a lot of miles, then it’s important to know that the engine sludge can sometimes provide a better seal between the pistons and cylinders and keep it from burning oil. Flushing the engine may end up cleaning up that seal, which can cause the engine to start burning oil.

When is it a good idea to flush an engine?


Can I Still Drive When My Car Needs an Oil Change?

If you have purchased a pre-owned car that has an unknown maintenance history or if it looks like the engine oil hasn’t been changed in a while, then an engine flush could help. However, just note that it might not be a cure-all either.

On the other hand, using a high-mileage or synthetic-blend oil regularly could be a better option. The notion behind this method is that most of the engine oils that you can purchase at the auto parts store are synthetic blends that will clean off the sludge and suspend the carbon deposits in it.

When the oil is changed routinely, then the deposits will be removed over time. It might not be as quick as an engine flush, but this method could be a much safer, albeit slower, way of removing built-up carbon and sludge.