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High Mileage Car ATF Flush


I have a 2004 Mazda 3s with 189K miles. I took it to a mechanic for changing the Automatic Transmission Fluid (ATF Flush). After reviewing the car mileage, the mechanic asked me when I has the last ATF flush done? I informed him that it was around 100K mile marker. He told me to “reconsider” and not to have the ATF flush as it may cause the transmission to break down (due to the build-up). I took his advice and left the shop.

I googled and found conflicting posts. Is he correct? Any advice?

i used to flush transmissions all the time on motorhomes, and i agree with your mechanic. sometimes when you use a machine to flush high milage transmissions it will actually cause more problems. ive seen it happen. so instead of doing a flush with a machine i would recommend taking it to your shop and having them drop the pan on the transmission to drain the fluidn and change the filter if equipped.

Good advice and good luck run together. Maybe. Avoid the flush.

If you don’t flush every 30k miles, you are better off getting a drain and fill. By flushing the tranny at 189k miles, the flush will break loose any debris or gunk that has been hanging on. Those debris or gunk may not get flush out. After the ATF fill, those debris and gunk can clog the tranny line and cause your tranny to over heat. If the tranny color is brown or it’s already too late to even do a flush or drain & fill.

I don’t have a problem with the flush as long as the pan is dropped and cleaned along with changing the filter before the flush is done. Many flush machines use the transmission’s own pump to circulate the fluid so it shouldn’t be an issue.

How often is the transmission fluid supposed to be changed?

if your owners book dosn’t have answer i do it every 30k

Thank you for all the replies! If I recall correctly, the owner’s manual does not specify an interval. I had it flushed twice before at 45K miles, then at 100K. I will ask for a fluid exchange and filter replacement. Once again - Thank you everyone!

My problem with ATF flushes is that people get the idea (because of marketing, in my opinion) that it’s perfectly acceptable to flush a transmission instead of dropping the pan, cleaning it and replacing the filter.
Like the other guys said, an ATF flush would be useful IN ADDITION to a regular fluid and filter service.
Have you ever looked at transmission filters that have been use for 30K miles and get replaced?! I wouldn’t want to keep those things in my transmission.
At least you’ve been getting your fluid replaced regularly. A lot of owners don’t even do that.