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What is an Engine Flush?

Malcolm Tatum
Updated Feb 13, 2024
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Engine flushing is a procedure that is used to clean the engine of sludge and other elements that build up in various parts of the machinery over time. The main purpose of this procedure is to prolong the life of the engine. By flushing an engine periodically, the internal components of the engine remain relatively clean and thus perform at optimum levels.

The process employed to flush an engine is somewhat similar to transmission flushing. With a transmission flush, the usual flow of fluid through the mechanism is used to push old fluid and various contaminants out of the system via the drain plug. With an engine flush, the cleansing chemicals are introduced and allowed to circulate through the engine, following the same flow pattern as the oil that lubricates the engine components. The chemicals eventually make their way to the oil pan, where the chemicals and the sludge they have removed deposit.

While in theory the engine flush seems like a task that should be performed from time to time, not everyone agrees that the flush is effective. While it is generally acknowledged that this process is helpful in low mileage vehicles that have not had the oil changed as often as recommended, some professional mechanics question the effectiveness of the flush with high mileage vehicles. The idea is that the buildup of sludge and deposits in the older engine may be more than the chemicals in the flush can process, resulting in making a bad situation worse. Instead of using an engine flush, they recommend that the engine be dismantled and the components thoroughly cleaned, assuming the engine is still in working order.

Because of the difference of opinion among professionals regarding the effectiveness of an engine flush, not every garage or automotive center will offer this service. Even among the mechanics who do offer engine flushes will generally evaluate the condition of the engine before recommending the procedure.

It is important to note that an engine flush is not a substitute for using the proper weight and grade of oil, or having the oil changed according to manufacturer recommendations. At best, it should be considered a way to augment proper maintenance and thus help to prolong the life of the engine.

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Malcolm Tatum
By Malcolm Tatum , Writer
Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing to become a full-time freelance writer. He has contributed articles to a variety of print and online publications, including WikiMotors, and his work has also been featured in poetry collections, devotional anthologies, and newspapers. When not writing, Malcolm enjoys collecting vinyl records, following minor league baseball, and cycling.

Discussion Comments

By anon946260 — On Apr 18, 2014

My girlfriend's mom has a 1998 Opel Astra she hasn't taken care of. Now the head gasket is blown. For several months now, she has been driving with coolant leaking into the engine. There is a huge amount of sludge build up. Massive! She can't afford a head gasket fix for another few weeks.

I'm sure the bearings are shot because she's driven like this for at least six months through extremely cold weather. Everybody has told her to stop driving but she hasn't. She doesn't understand the consequences. She does short trips to the store almost every day.

That said, I'm trying to do a "stop gap" attempt at giving her engine a fighting chance until it gets some help. I wanted to do an engine flush on it. Not sure if it's worth it. It certainly won't help the head gasket, but I thought at least it may help lubricate and clear up the lines for the oil. My worry is that I throw in the additive and because of the build up, I don't get everything out or create a bigger problem that will require a total rebuild. Can anyone help?

By anon930071 — On Feb 03, 2014

I have a 2006 330i. In July 2013, I had the vehicle serviced for a cooling system flush, because I received an email reminder to have it done to prevent future cooling system failures.

My question is now, almost seven months later and (how conveniently) there's a leaking lower radiator hose, the coolant temp sensor needs replacing, and the thermostat and water pump need replacing. Is this even remotely possible to have all fail at the same time and how come this wasn't known six months ago when the system was just serviced?

By anon331551 — On Apr 23, 2013

I see a lot of hate for engine flushes on the internet. It's kind of like buying anything, really. If you don't put the research in, and just buy what they sell at the grocery store, you're more than likely going to end up with something that isn't going to be the best for your motor. However, you also have Pro-Tec Autocare which was engineered for mechanics to use during routine maintenance and servicing. This engine flush is certified by the super strict German Technical Inspection Agency and provides superior lubrication during the engine flush procedure. It will increase the old oils lubrication by almost 90 percent during the flush so their is no cause for concern on lower end bearings. We've tried seafoam as they have been around forever, but it doesn't even stack up when compared to Protec.

By anon236659 — On Dec 24, 2011

I was charged 850 for 20 k service of swift vdi. Is it reasonable or just like that?

By anon229809 — On Nov 15, 2011

Having an engine flush done under pressure through the oil cooler lines is a very effective service to help eliminate valve train deposits from affecting components such as vvt, and valve stem seals. Pouring in a can of flush and running your engine is not only a waste of time, but can be damaging to lower end bearings. Flushes should be done by a professional with proper equipment, not some dumb backyard fix like using a quart of trans fluid or diesel.

By anon122496 — On Oct 28, 2010

i believe an engine flush killed my engine. i read an article stating it actually does more harm than good. they were right.

By anon47500 — On Oct 05, 2009

There seem to be different "forms" of engine flushes. There are high-speed/pressurized systems that "flush" out the engine, not exactly sure how. Then we have other techniques such as emptying one quart of oil from the crankcase, add 1 quart of kerosene, and then let the engine idle for 5-10 minutes. Then another similar, is the "seafoam" treatment, in which you add 1 fl. oz. of "seafoam engine treatment" per every quart of oil your crankcase holds; drive the car safely (don't hammer on the gas pedal, or doing any sporadic driving out of the norm) drive the vehicle to your oil change location, and get your lube oil and filter change done, with the vehicle as hot as possible. Keep the engine idled in the parking lot until they can service you. The Seafoam (which is a 100 percent petroleum product), IPA, and some other cleaning agents works by cleaning up the internals of the engine, which is less harsh than these "pressurized" systems that some of these quick lube places perform. So anyway, get the oil changed, and after it's done, I always like to look under the hood, check the oil levels, and make sure everything is to spec, and then add more seafoam (this is post-oil change), same as the pre-oil change, one oz. of seafoam per every quart of oil. Every gasoline fill up, you want to monitor the level and color of your oil (which is why I also mentioned to check the color after the oil change, while in their parking lot). When the oil gets dark, it's time to change it. But, don't drive anymore than 3000 miles on this "seafoamed" oil. Depending on how much sludge you had built up, you may not even experience black oil at the dipstick, but don't go anymore than 3000 miles on this oil. After this, just get the lube, oil, filter, changed as normal. Perhaps upgrade to a synthetic, or even a synthetic blend for added protection and engine longevity (some oil advertisements even claim an increase in MPG using synthetic. who knows, though). Seafoam is s straight 100 percent petroleum product, but also contains other additives to help clean out your crankcase and other "innards". So it won't "thin out" your oil at all. The thing you've got to be careful for, is older engines, or those with excess sludge, having that sludge get freed up, it's no good driving on sludged up/softened oil. Which is why I recommend the initial "flush" then the second/post "treatment" to soak up the remaining sludge that may be left behind. Last of all? Don't skimp on your oil. Demand the best, do your own research on oil and get the best for your vehicle, if you want your vehicle to last.

Malcolm Tatum

Malcolm Tatum


Malcolm Tatum, a former teleconferencing industry professional, followed his passion for trivia, research, and writing...
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