I repair automatic transmissions and all I can say is, that the information that an oil change or flush, which is an oil change, destroy your transmission is incorrect.
New oil, or a flush with new oil specified by the manufacturer cannot harm any transmission!!!
It's absurd to assume that old, used ATF oil with residue floating in it, won't damage transmissions, but new ATF oil made specifically for those gearboxes, should cause damage. And why should that be different on an enginge, a transfer case, a power steering or differential?
The reason many transmissions fail after a transmission flush is this: Most people completely neglect servicing their transmission until the transmission shifts poorly or causes other problems. Then they run into the workshop and the mechanic says: We can try an oil change. But then maybe it's already too late, an oil change is done and shortly afterwards the gearbox fails and then these people claim that the oil change broke the gearbox.
In this area the opposite is true – old oil destroys transmissions. The lubricating effect of oil is based on the fact that there are long carbon-hydrocarbon chains in the oil that can slide past each other. When exposed to mechanical stress, as is naturally the case with transmissions, these chains are destroyed over time. This causes the oil to lose its lubricating effect. Additionally you have wear of the Clutches which contaminates the oil. Depending on the transmission, it is important to change the oil at least every 35,000 miles..
So is it better to do a DIY oil change with removing the pan, change the filter and fill in the drained oil? Or is a professional oil flush necessary, better, or even dangerous?
To make things clear:
In an automatic transmission, two thirds of the oil is usually not in the pan, but somewhere else in the system, for example in the torque converter, the oil pump, or in the oil cooler. If you remove the pan you only get a third of the oil out. That's not a real oil change.
If you want to change the oil properly, you have to flush it, which means you add oil to the gearbox while draining the old oil. It's not magic, it's just replacing the oil that's in the system. There are no cleaning agents used, only old oil is replaced with new oil. That is "flushing the transmission".
Because it's not easy to do that on a not running transmission, Workshops have special flush machines which cost a lot of money. They connect these machines to the transmission, mostly on the oil cooler, push in new oil and suck out the old oil oit, until the complete oil is changed.
And they change the filter
From my experience, most automatic transmissions only have paper filters or even flow filters that are intended to catch large chunks that may have broken off somewhere before they enter the oil circuit.
The normal wear in an automatic transmission is so fine that it's enough to change the oil regularly, they don't have to filter that out. There are no combustion residues like in engine oil, which have to be filtered out with fine filters.
That means for someone who want to do it DIY that the biggest benefit is flushing the oil, a little benefit is to change the filter. Flushing the oil is very easy and done in half an hour, exchange the filter is a little bit more complicated, because you have to remove the oil pan under the car and you have to get that oil pan sealed again.
So my recommendation is as we say in Germany: "Let 5 be equal" and flush your oil and change your filter only when you want to and have the abilities to do it.
Of course, if you buy a used car and don't know the service history and condition of the transmission, it's a good idea to remove the oil pan, put a new filter in it and then flush the system completely.
This is particularly helpful, because you can determine the condition of the gearbox by looking at the adhesion to the magnet, which is normally supposed to catch fine metal debris in the oil pan. No question. It is good to change the filter, especially when you don't know how long the filter is in use, but it's definitely not necessary to change the filter at every oil change.
So, once you've done that, you can do without changing the oil filter the next time when you change the oil.
And here comes the good news:
It's super easy to change the oil on our trucks. You simply remove a line from the oil cooler at the front, near the air filter. There is even a quick coupling for these purposes. And connect an appropriate hose on the cooler, let the engine run briefly until there is no more oil coming out, that's about 4 quarts, then refill the appropriate amount and repeat this three to four times. If you let the engine idle and let spill out oil until nothing comes anymore and directly switch of the engine, there is no danger to make a damage on your transmission. Automatic transmissions do not have thrust bearings that run under oil pressure, like the connecting rod, crankshaft or camshaft bearings in an engine. With an engine you should never do this and let the oil run out until it stops flowing. With an automatic transmission this isn't a problem.
This flushes the gearbox, it takes half an hour and costs maybe 5 Gallon of oil, which is not very expensive. Then you reconnect your oil cooler, check the oil level and you are done. Just to be complete you need to check the oil level when the transmission is on working temperature. So drive and check again.
Basically, relatively normal dexron 6 oil is enough - you don't have to use gold-particled, hand-signed oil from freshly pressed slate layers in the Oil Valley in Dubai.
Better change your oil without filter change every 15,000 miles with normal priced (not the cheapest) oil than: Flush your gearbox in a workshop with filter change and expensive oil, only each 100,000 miles.
Only my 2 cents
