Why is this always the recommendation? And before anyone goes into the whole “old fluid can be gunked up or have metal particulate in it that a flush forces free and into places it shouldn’t be causing problems,” I already know all of that.
I ask this because both my dealer and my independent Japanese-make specialist generally recommend and only do “flushes” (I’m sure they’d both do a drain-and-fill if asked, but I digress). My understanding is that there’s more than one type of flush. They do them under the car’s own normal operating pressure. The type that I think everyone is vehemently against is that which is done under significant, external/artificial pressure. I can’t see how the version of a flush that uses the car’s own pressure could be harmful since this would in theory be no different than what the transmission experiences while you drive down the road. What am I missing?
Of note, I service all of mine at 30k mile intervals, so there should never be excessive gumming up or dirtiness to my fluid to begin with.
Automatic transmissions work at relatively low pressure when you flush our transmission you are pushing pressurized fluid throughout the system that can clog things up and even cause damage over the years I have seen hundreds of transmissions ruined that did not work right after flushing when they work perfectly fine before
I agree that if done properly, the pressure isn't a problem and shouldn't harm a healthy transmission.
However, flushing is an invasive, and usually unnecessary procedure. If you can avoid touching the cooler lines, you should. The transmission has a removable pan for a reason. If you maintain the transmission regularly, a drain & fill and new filter is all it needs. Transmission specialists have confirmed this to me, but you can ask them yourself and see what they say.
So are there actually two versions of a "flush?" That's what I'm getting. The dealer and my independent shop says what they do is low-pressure. Oddly, though, the independent will replace the filter. The dealer says they do not service the filters at all. I thought that was weird and didn't even think to follow-up with "why?"
The risks of flushing far outweigh the benefits. You can never be sure that a mechanic will do it properly. There's too much opportunity to screw something up. The drain and fill is a safe way to reliably maintain an automatic transmission.
If the transmission has a serviceable filter, then it should be changed. They're inexpensive, and if they plug up, it can ruin the transmission.
My understanding is that there’s more than one type of flush. They do them under the car’s own normal operating pressure. The type that I think everyone is vehemently against is that which is done under significant, external/artificial pressure. I can’t see how the version of a flush that uses the car’s own pressure could be harmful since this would in theory be no different than what the transmission experiences while you drive down the road. What am I missing?
You are absolutely correct. The key is how does one know which of those “flushes” is being performed? So if flushed, it is important to know exactly what is really happening (and it helps to see it for yourself). It’s easier and safer then to just ask for a drain and fill, but do it often. On some Ford vehicles (and maybe some others - unsure which ones), you can only exchange fluid with a “flush” (so no drain and fill).
Gotcha. Good info! Glad someone could confirm what I was understanding. Again, I only let my dealer and/or indy shop do it. I wouldn’t touch a Jiffy Lube, Pep Boys, Tires Plus, etc. with a ten foot pole. I’ll check it out to see what they do one day as you suggest, but I trust both as I’ve used them for years and had good dealings. Appreciate the input!
I get what you’re saying. It’s the margin for error that increases the risk. I guess I’ve just always had it stuck in my head that doing only a drain and fill effectively contaminates all of the new fluid with old fluid, so that just seemed counterproductive for longevity. But what do I know? {black}:grinning:
The drain+fill has been done reliably for decades, and like Scotty said, hundreds of transmissions died from flushes. Undoubtedly, many were done at dealerships. Unless you have a very unusual situation and the fluid is badly contaminated, don't do it. Your fluid will never be perfectly pristine and sparkling, even with a flush, so perish the thought.