Drain and refill vs. cooler line flush

[Falcon_LS]

Call me mad, but I never really saw the point of doing a simple drain and refill...especially considering the torque converter is where much of the fluid is held and you're just draining what's in the transmission.

Whenever I service my transmissions (generally every 25,000 miles), I always take the time to do a cooler line flush, drop the pan, replace the filter and the gaskets, clean them out and fill up to the correct level. 10,000 kilometres (6,250 miles) prior to the service, I dump in half a bottle of ARX as well. My transmission's capacity in the Pajero/Montero, for instance, is 7.2 litres and I usually use about 12 litres or so to flush it all out.

I've recently had people telling me this causes more harm then good. Considering you're dumping out the old fluid for new, and immediately notice an improvement in shift quality afterwards, I do not see how. Having said that, does a cooler line flush (at the recommended intervals) help extend the life of a transmission, because the old fluid is completely being replaced with fresh fluid regularly?

Just a random thought. Thanks.

 

[bmwtechguy]

Consider the million mile van guy who has never dropped the pan on his transmission, but does have the flush done every 50k miles IIRC. I think the complete flush is more important than the pan drop and filter change. That filter is not really fine and is not in real danger of plugging shut, although I am inclined to change anyway when I do a complete flush.

 

[JHZR2]

They key with ATF has always really been the loss of viscosity first and foremost, IMO. After that, yes, a refresh of the add packs, and after time at temperature, oxidation too...

Sure, doing a pan drop does not get all the fluid... but a flush does not change the filter. Either are a pain - pan drops are a hassle, taking cooler hoses off, depending upon the connection style, can damage radiator connections and cause leaks.

I find the easiest is to do a pan drop and filter change as required per the manufacturer and service, and then doing a quick swap of fluid via an oil vacuum every oil change. This keeps a few quarts in rotation at all times, and is free, clean and simple to implement.

 

[bepperb]

The same amount of fluid gets replaced either way. Both are a pain. The drain/refill is because it's more than one trip under the car. The cooler line is especially if the line on the car is too short to get to a bucket in good position, or if the clamps are hard to use, and if you only have one person can be sketchy.

I don't see how one is better than the other. It's just personal preference. 3 drain/refills is about 50% -> 75% -> 87.5%. JMO, but you're not getting any more than that on a 12 quart cooler line flush.

 

[jcwit]

I had an adapter welded on my pan and do a drain and add every other oil change. Quick, simple and easy.

 

[JHZR2]

+1, this is IMO the best way to do it if you can get a pan set up like that. Personally Ive never trusted the self-install drain plugs, but welding one in is likely sound.

 

[NightRiderQ45]

drain & fill every 15k is good for me.

 

[unDummy]

30k cooler line flush is reasonable for most transmissions. So, your 25k maintenance program is pretty much optimum since you're taking care of the filter, pan, all of the ATF......very thorough.

With a quality ATF, you don't need ANY additives.

Maintenance does not cause harm as long as it is done properly.

I prefer drain/refills since all my cars have ATF drain plugs. So, my drain/refill regimen is usually 10k or so, which is equivalent to the 30k full ATF exchange.

If you want to extend the intervals, then an external ATF filter should be considered.

If the vehicle is in a hot climate, or used for work(towing, plowing, hauling), then an extra ATF cooling needs to be considered also.

 

[JakeR22]

Some car don't have pans to drop, and filters to change.