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If you take your car to a shop for a routine oil change you have a high probability of being told your car needs one or more of its critical fluids flushed, changed or serviced. This started originally at the quick-lube shops and spread to the whole auto repair industry, including the dealers.

Part of the reason is technology. New machines have made it possible in most cases to change the fluids quickly and easily, or so the sellers of the machines say. But the real driving force is profitability.

Today I'm changing a timing belt and water pump on a Dodge Caravan. It will take all of five hours of bay time, a lot of parts and a lot of potential liability. In half the time I could do a series of flushes with little effort or liability and make much more profit. Since most people, mechanics and shop owners included, respond to economic incentives, it is coming to pass that every car going to every shop needs every fluid flushed every day.

In short, what is really being flushed is your wallet. It is straining the credibility of an industry that rightly or wrongly has always had credibility problems.

The Four Flushes

Old-timers from the '50s, '60s and '70s always knew it was a good idea to periodically drain the radiator, put a bottle of flush chemical and water in, run it a half-hour then wash it out again with plain water before refilling it with the proper mix of antifreeze and distilled water. Or if you wanted to do a really nice job you could cut one of those plastic flush tees from a Prestone flush kit into the heater hose, allowing you to hook a garden hose up and run a continuous flush.

Now these old-timers are being told their transmission fluid, power steering fluid, and who knows what else must be flushed on a yearly, monthly, or even daily regimen. Strangely, their '77 Olds Cutlass managed to run 180,000 miles without all this attention.

Now don't get me wrong. I am in favor of changing most fluids at 30, 60, and 90,000-mile intervals, regardless of what the owner's manual says. But that is not what's happening. These services are being oversold to a degree that is bound to damage the reputation of our industry to the net result that consumers will not believe any of us, even when we are telling the truth.

The Rundown

Let's start with the automatic transmission -- the most frequently flushed fluid besides the radiator. The advent of the transmission fluid exchange machine was a great step. In the past, automatic transmission fluid could only be changed by removing the transmission oil pan, which only holds three to six of the eight to 10 quarts in the transmission. The second you started the car, the new fluid mixed with the old, eliminating much of the benefit of the service.

The fluid exchange machine, which some people choose to call a flush machine, cuts into the transmission cooler line at the radiator. As the car runs, old fluid goes out into the waste tank while new fluid is simultaneously pumped in. If the shop is really thorough, the car is lifted and actually driven through all the gears while the exchange is taking place. And if the service is done properly, the transmission oil pan still has to be removed and cleaned and the filter replaced -- a solid hour and a half of work. So if a quick-lube shop is offering it to you in 35 minutes, something's not being done.

Now, as to checking the dipstick for color or smell to determine if your fluid needs to be changed: At the extremes (not changed for 100,000 miles or changed yesterday), you can tell. But as far as whether it was changed 3,000 miles ago or 20,000 miles ago, no one can know, and if they say they can, they are lying.

Power steering fluid in general is not listed in most maintenance schedules as needing periodic replacement, although there are some exceptions. But we have a machine for that now too, so expect to be told you need your power steering fluid flushed. Look, if every three to five years (45,000 to 60,000 miles) you change your power steering fluid, that's not a bad idea. And replacing it with synthetic fluid, if allowable, is even better. But you certainly don't need to do it yearly or even every two years.

Brake fluid lives in a sealed environment because exposure to moisture will ruin it. No one ever dreamed of messing with it until Hondas became popular, and Honda for some reason does call for brake fluid replacement. Now we have (you guessed it), a brake fluid flush machine. If your factory manual calls for it, by all means, change your brake fluid. Other than that, leave it alone unless you are having brake repairs done, in which case changing it may not only make sense but be necessary if the hydraulic system has been compromised.

It is not enough that you are changing your oil every 3,000 miles. Now when you go for your oil change they want to hook up a motor flush machine to clean your oil system out. Strange, my '63 Valiant didn't need that. Look, this goes under the category "If you need it, it won't help" -- and thus sales are being encouraged on vehicles that really don't need it. If an oil system is dirty enough to have deposits of sludge forming, you're only going to get the sludge out by removing the valve covers and oil pan and scraping it out. Any stirring up of the stuff without removing it is likely to do more harm than good.

Stocking Stuffers

I had an oil-change guy who lasted about a month. Every time a truck or sport-utility vehicle came in (the only vehicles left with a classic differential), he would call me over, waving his finger at me after having dipped it in the differential oil, saying "it needs a differential service," as if he who barely knew how to open a hood would know. Evidently it was a service heavily pushed at his last place of employ.

On a military 6x6 doing heavy duty in Iraq, differential oil needs constant attention. On a domestic SUV whose only off-road experience is driving onto the grass at the soccer field, just follow the owner's manual or change the fluid every 60,000 miles. The exception would be if you tow things or if you submerge the differential by backing a boat into the water.

Oh, and the transfer case fluid need only be changed at the required mileage or 60,000 miles.

Avoid the Wallet Flush

The easiest way to avoid having your wallet flushed is to try to stay with one shop that you trust, and keep good records. Now I know that even my best customers occasionally go elsewhere for an oil change when my shop is not convenient. So if you find yourself in a strange shop being told that the very lives of your children depend on your getting a particular service at that moment, just walk away.

Well, actually, that would be a tough one. But a new customer is often viewed as fresh meat, since all their existing customers have been flushed into the next galaxy. The harder the sell, the more you must resist. And believe me, the sell can be pretty rough. They can come at you with test tubes of fluid samples, and with pH strips whose color change indicates you are seconds from disaster (all provided by the flush machine manufacturers). Even my sister-in-law, whose toughness and command of Arabic swear words sent Egyptian border guards scurrying for cover, succumbed once.

And to the people in my industry, the owners and shop managers, I say, "What is it going to take? Another '60 Minutes' or 'Nightline' exposé where they go shop to shop and find out how many flushes they need after chemically certifying the fluids as new? Do you know how tough business is gonna be after that happens? Try thinking a little farther ahead than next week's bonus check."

Doug Flint owns and operates Tune-Up Technology, a garage in Alexandria, Va.



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