Auto Shop Fluid Flushes Are Rarely Needed, Can Cause Damage, and Hardly Ever Fix Problems
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Auto Shop Fluid Flushes Are Rarely Needed, Can Cause Damage, and Hardly Ever Fix Problems

Though service advisors and mechanics may tell you otherwise, fluid flushes are almost always unnecessary and can do much more harm than good

July 5, 2021

Have you seen the displays at your auto shop advertising fluid flushes designed to protect your major vehicle systems? It may seem like a good idea, but fluid flushes should be done sparingly, if ever. Vehicle fluids lose color quickly since color is added mainly to help you distinguish between the different types of fluid, not the fluid's condition. Some flushes even damage sensitive vehicle parts.

Don't Flush for routine maintenance

You'll likely be inundated with an exhaustive list of recommended service items when you have your vehicle checked out. Quite often, these recommended repairs are too soon or just unnecessary. The automotive fluid flush is one of those recommended service items, especially since it's a major money maker for the ship. Most of what you pay is a labor charge and the markup on fluids is already high.

In a majority of cases, the average driver doesn't need these expensive fluid flushes. Automotive fluid is designed to go through the extreme. You do need to change your fluids periodically since it breaks down over time, but flushing is usually unnecessary. In fact, many vehicle manufacturers recommend against the practice as a matter of routine maintenance, reserving the practice for only cases of extreme catastrophic component damage where metal particles may be floating through the system. So don't feel compelled to have a flush unless your maintenance manual specifically calls for it.

Financial Incentives can get in the way

The service advisor working with you usually has a financial incentive to get you to spend more money, especially at franchised dealerships. Most of these service advisors are only paid commission, not a steady hourly wage.

That in itself shouldn't cause you to worry. But money is a powerful motivator and can motivate a service advisor with the best of intentions to push you into services or repairs you don't need. In these cases, you may get pushed towards a fluid flush when a simple fluid change is needed. Your service advisor might even say that a flush is required or may even say your fluid needs to be changed sooner than necessary.

Color is not an indicator of wear

With the exception of motor oil, brand new vehicle fluids are usually dyed a particular color to indicate the particular type or specification. Transmission fluid is usually red, but it darkens over time like motor oil. But the amount of red dye remaining doesn't indicate the condition of the fluid. Dyes degrade with time and heat, so don't think a darker color transmission fluid is any less robust than fluid that is bright red. The fluid does get darker as it gets more fine metallic particles in it. But that doesn't necessarily mean the fluid needs to be flushed or even changed. It could still function as intended for many more years. But most people associate dark with dirty, which is why the displays at shops show brand new fluid side-by-side with older 'dirty' fluid. It's not uncommon for a brand new vehicle to have 'dirty' transmission fluid at the very first oil change, which could be 100,000 to 200,000 miles before the first recommend transmission service.

If any of your fluid looks 'milky,' a fluid flush or change will not fix your problem. This is one time when color does indicate something serious. Transmission fluid should not look like strawberry milk, coolant should not look like curdled milk, and engine oil shouldn't look like chocolate milk. This color change indicates fluid cross-contamination and serious and costly problems could result if not corrected immediately.

flushes are Not a miracle solution

Regardless of what you may hear or read, a fluid flush will never fix a broken seal, will never fix a malfunctioning sensor, will never repair a slipping transmission, and will never restore vitality to worn components. The only way to address these items is to replace the damaged or malfunctioning parts or to make the necessary adjustments. If you hear someone telling you that a fluid flush will or even might fix your problem, look for service elsewhere. And always get a second opinion on a tricky problem.

Follow your maintenance schedule

The maintenance items and schedule recommended by your vehicle's manufacturer is usually the only maintenance you will need aside from replacing or adjusting other components that simply fail due to age or wear. The engine won't perform any better by having every last trace of old oil flushed out. The same goes for other vehicle systems.

Beware of 'real-world conditions' sales pitches

Always be skeptical when your service advisor or mechanic tries to push you into a service, including fluid flushes, because of 'true' real world conditions. You may hear it described in such a way that suggests the vehicle manufacturer's service schedule is inadequate based upon the real world conditions the staff have seen. Or they may say it as a recommendation based upon unique local conditions, driving styles, etc.

Car manufacturers don't design a car from start to finish in a few weeks. Those vehicles, even the least reliable ones, go through years of extensive testing in conditions that range from the coldest of the cold to the hottest of the hot under extreme stress. It's an attempt to get fluids and parts to fail so they can be improved before mass production begins. There aren't any real-world conditions on your daily commute that will compare to any of those extremes. Your service schedule is designed with that in mind. So if you are getting a recommendation to change or flush a fluid more often than is required as per your maintenance manual, look elsewhere for service.

When might you really need a fluid flush?

Unless your vehicle's maintenance schedule specifically calls for a fluid flush, you should never need one. Some manufacturers do require a flush as part of regular maintenance, but it's not too common.

You may need a fluid flush in these cases:

  • A system suffers a catastrophic failure that contaminates the fluid with debris.
  • The fluid becomes contaminated with other fluids, such as transmission fluid being contaminated with coolant and brake fluid being contaminated with water.
  • Components in a system have become clogged with debris or stick due to varnish buildup.
  • An incorrect type or specification of fluid was installed in the system.
  • The maintenance manual specifically calls for a fluid flush.

Some Fluid Flushes can cause damage and problems

Some vehicle manufacturers have been advising technicians against the use of fluid flushes as a matter of routine maintenance. Many fluid flush machines use chemicals to help clean the system. Some of these chemicals can damage internal seals and sensors, causing malfunctions down the road that the shop will then repair for the customer (for a fee). Even if the parts don't fail immediately, repeated flushing can cause accelerated damage.

Even if the chemicals don't damage the system or no chemicals are used, it's not often a good idea to flush fluid as a matter of routine maintenance. Many of the systems are designed to have debris and contaminates collect in a filter, on a magnet, or both. Pushing clean fluid through the system can dislodge the contaminants in the filters (if not changed), on the magnets, or that have deposited elsewhere in the system. These contaminants can then deposit in other areas if they aren't removed and cause problems, especially in the pressure-sensitive areas of an automatic transmission.

Flushes and Sludge Buildup

Your service advisor or mechanic may tell you that a fluid flush can remove sludge buildup caused by years of inadequate maintenance. But it usually isn't a good idea. If your engine is full of sludge, there are worse problems you must first consider other than simply cleaning it out. Sludge indicates neglect, which means that there is likely a lot of accelerated wear and tear inside. At that point, replacement may be a cheaper option than the cost to disassemble and properly clean it.

If you do have a lot of buildup caused by improper maintenance, a fluid flush with a chemical cleaner may clean the system but could cause the component to not function normally anymore. Removing the buildup can change the way the parts move inside or the fluid pressure, which can change how it feels and works. Buildup inside the component may even be filling gaps between seals and gaskets, which may then leak after cleaning.

In these cases, make sure the parts are cleaned and repaired properly. If the neglect has been severe, replacement may be required. In some cases, manufacturers have special cleaning procedures and sometimes additives that can be put into the system between normal fluid changes to restore normal operation.

Drain and fill is fine

Most vehicle manufacturer service schedules will only advise you to change a particular fluid. It may also be listed as "drain and refill." Unless your vehicle's maintenance schedule specifically advises you to flush a fluid, stick with simply draining the old fluid and refilling it with new fluid. It's true that a drain and refill won't get every last drop of oil fluid from your system. But that's one of the reasons your maintenance intervals are set the way they are set. Remember that while a drain and refill can't get every drop of oil fluid and every contaminant, the best flush machines can't get everything, either. And if you're doing an oil change and want to get as much of the old stuff out, change your oil, drive a mile or two and change the oil and filter again. It's cheaper and safer than a flush.