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Transmission flush

My mechanic says now it is possible to flush the entire transmission rather than just changing the fluid, and recommends it. Is it possible this could disturb the transmission culture/environment - don’t component working parts have a memory of what is customary, and any change for the better could actually be a change for the worse by throwing things off?

Yes, it is possible to flush the transmission.
And, it is possible to do incredible damage to a transmission by flushing it, rather than changing the fluid.

All too often, mechanics interested in a fast buck will flush a transmission without first changing the trans filter. This approach is likely to force debris from the filter back into the transmission, causing damage. The best approach is to drop the trans pan, clean it out, install a new filter and pan gasket, and refill with fresh fluid. If your mechanic insists on doing only a flush, then you must insist on a new trans filter before he does the flush.

Incidentally, if you are contemplating a flush because the transmission is acting up, it is probably too late to save it. The fluid and filter should be changed every 3 yrs/30k miles in order to prevent problems.

Transmissions were designed to have the pan dropped, the fluid DRAINED and the filter replaced. Flush toilets… not transmissions! I would also flush your mechanic as anyone who recommends a transmission flush is not competent enough to air your tires.

Trans not acting up at all. Had fluid change about 3 years ago. He would chang filter before flush, but can you tell me if there is any rationale to flushig? It is said to prolong the life of the transmission. I have a 97 Lumina, 149,000 miles, and no trans problem.

On most transmissions (e.g. those without torque converter drain plugs) dropping the pan and changing the filter only changes a portion (variable) of the fluid. If this is done every 30K or so this isn’t a problem.

If one does want ALL of the old fluid out and ALL new fluid in then a fluid exchange can be done via machine - but should only be done AFTER a new filter (as noted).

If you are servicing it regularly, just service the filter and forget about it.

Not competent?

I do transmission fluid exchange services all the time. And when done correctly can allow a transmission to go many miles without a problem.

Ask the owner of a 1998 Toyota Camry with 190,000 miles on it. Original automatic transmission. Fluid exchanges done every 30,000 miles.

Ask the owner of a 1999 Honda Accord with 230,000 miles on it. Original automatic transmission.

Ask the owner of a 2000 Ford Taurus with 250,000 miles on it. Original automatic transmission.

Now ask the owner of a 2000 Chrysler Cirrus with 78,000 miles on it. Only did one pan drop fluid exchange at 35,000 miles. Needs new transmission.

Ask the owner of a 2004 Chevy Silverado with 120,000 miles on it. Two pan drop fluid exchanges at 50,000 miles each. Needs a new transmission.

If doing transmission fluid exchanges makes me incompentent to even put air in a tire, then that must mean I don’t know what end of a scredriver is the business end when I recommend an oil and filter change?


I perform Transmission Fluid Exchanges all the time as well, there really seem to be a lot of misconceptions about what is involved in a transmission flush. Yes the machines that use detergents (flush chemicals) and force fluid through the transmission using high pressure can cause damage to it, but a cooler line flush is noninvasive.

If you don’t have a machine and you really want to provide max protection to the transmission without taking it in and paying the ludicrous service fees (the local Ford and Toyota dealers now want to charge me $250-300 for this service!!!), and you don’t have a trans pan plug (curse you, Ford!), then you can probably do what I do:

  1. Go out to Harbor Freight and buy a fluid transfer pump. I got mine there for $2.99. Or you could get a Mityvac fluid extractor - they’re VERY nice but $60-100.

  2. Every year, suck as much fluid up the transmission dipstick as you can using the fluid pump. I can generally get 7 quarts out of the pan this way out of the 13.5 that the whole system holds. Then just refill the transmission through the dipstick. Cost: ~$35 for two gallons, leaving a quart to spare.

  3. Every other year, do the above service, but before refilling the transmission, drop the pan and clean it and replace the filter. Sucking the fluid out first makes the pan drop a MUCH cleaner job (my car’s normal fluid level is above the level of the gasket, so if you don’t suck the fluid up first, it spills everywhere when you crack the gasket. Cost for this service: $35 for the fluid and $32 for a filter from the dealer (I prefer dealer filters here as it is cheap insurance over the $18 aftermarkets, and my car has multiple filters depending on VIN #, so aftermarkets aren’t always perfect matches).

So that’s $51 per year for servicing.

After 10 years or so of doing this, you’re pretty much at a steady state condition where the fluid (by volume) averages 11 months old after a change, 23 months old right before a change, and 1.429 years old over the course of the year.

After 15 years, you still have some original fluid in your transmission. But it only makes up 0.36% of the total volume of transmission fluid. Big deal.

Do that and accelerate modestly and your transmission should last you a LONG time. If you want to save even more, I’d say you could change the transmission filter every 3 years instead of 2 without any real increased risk.


When you do your fluid exchanges, do you ALWAYS recommend changing the filter before the exchange?? If the customer declines the filter change, do you decline to perform the exchange??


Sorry you got caught up in my very wide net. There has never been a reason to flush a transmission other than to sell more transmission fluid. Vehicle manufacturers do not recommend transmission flushes as a whole. They do allow some flushing with certain machines and for certain procedures. Flushing transmissions as preventative maintenance is flawed logic.

Mechanics should always avoid the “potential” to do harm to a vehicle at all costs. Flushing is not 100% destructive and I know that. If done properly a transmission may not be damaged at all. On the other hand, why take the chance? That’s why a mechanic who advises a procedure that may do more harm than good is incompetent in my book. I’m sure the vast majority of mechanics will agree with me and I stand by my comments. I have personally seen friends and family shell out for new transmissions right after a transmission flush. I have never had a transmission failure and I have never had one flushed either.


Good advice!

There’s nothing wrong with transmission flushing if it’s accompanied by dropping the pan first, followed by cleaning it out and changing the filter.
Would you change engine oil and not the filter? The fuel pump and not the filter? Fuel injectors without changing the fuel filter? An A/C compressor without changing the drier or accumulator?

There’s also another benefit to dropping the pan. This allows you to inspect it for something out of the ordinary. Too much crud in there or any abnormal metallic shavings could mean that the transmission may not be worth flushing and may provide a heads-up about taking any trips out of town.