Full Flush Of Auto Box

[9690phil]

If you drain, then put say 3litres of new fluid in to replace what came out then drive for a few miles then repeat again are you not just loosing the new fluid you have just put in?

[cruisermark]

If you drain, then put say 3litres of new fluid in to replace what came out then drive for a few miles then repeat again are you not just loosing the new fluid you have just put in?

no - over time you oil will be alot newer because you are adding new oil - and perhaps it will have a less shocking effect on the transmission as apposed to doing a complete empty and refill.

[alanr]

This subject of ATF oil changes crops up on the forum fairly regularly over the years, and always seems to divide into two camps - the 'dos' and the 'do nots'.

On the Mk 4 the service schedule is for a fluid change every second 'B' service, ie at 36.000, 72,000, 108,000 etc. In Lexus speak "Fluid change" means drain what ATF is in the oil pan and replenish - normally about two litres can be drained off this way. This does not constitute a flush of the transmission, of which approximately a further ten litres of ATF will be held in the torque converter, transmission cooler, pumps and associated pipework.

My last service at a main Lexus agent was at 108,000 miles back in 2008, and despite being previously assured that all items on the schedule would be carried out, all they actually did was a standard B service without reference to overall mileage or time. When I queried the lack of fluid change, the Service Manager stated that the transmission fluid on the dipstick was a nice colour, and didn't need changing.

Quite true, the dipstick oil did present a fairly healthy pink complexion, but as others have noted, this is not necessarily indicative of the true state of affairs. I therefore decided to do a fluid drain and refill myself. The fluid that came out was not pink and healthy when viewed in bulk, and had a distinctly purple/brown colour, with non of the clarity of new Type IV fluid. Proof positive that appearances can be deceptive when viewing the oil condition via the dipstick.

Quite by accident, I discovered that after having left my car with its nose up in the air overnight on a set of ramps, a further three litres of ATF could be drained out of the pan, having drained back down from the torgue converter etc. So, five litres of fresh Type IV later, I had a dipstick that really did look "in the pink", and still does.

I'm not an advocate of flushing auto boxes unless absolutely necessary - it can sometimes disturb sediment and cause more problems than it cures. I am however an advocate of draining two litres out every 36,000 and replenishing, as per the Lexus schedule. Aisin gearboxes are generally very reliable indeed, but I can't help but feel that the drain and refill has been put in the schedule for a good reason. For those who have horrible brown sludge or the smell of burnt ATF fluid, I see little alternative but to try and replace as much of the fluid as is practical. Regular drains and refills may just have the edge over a full blown flush.

The one thing that I would emphasise is the importance of using Toyota's Type IV fluid in the Aisin gearbox - they tend not to like Dexron or other alternatives, no matter what the manufacturer's claims as to meeting the correct specification.

Regards, Alan

[39buss]

When I took the rad off my MK3 a few years ago the oil cooler located in the bottom of the rad spilled out horrible sludge. Maybe this is why LS 430's are having g/box problems now. Regular partial changes, as has been suggested, letting the old and new dilute with each other may well be the way to go, certainly the easiest.

[Cotswold Pete]

I knew it would be stirring the next a bit by starting this topic, but seems like a good synthesis of the debate.

I do kind of agree that full draining may now not be the best way.

Came across the following on a Soarer (this link is interesting to read)

But he does suggest a method of testing the 'goodness' of the ATF - which is

A quick way to test for worn transmission fluid is to do a "blotter" test. Place one or two drops of ATF from the transmission on a paper towel and wait 30 seconds. If the spot is widely dispersed and red or light brown in color, the fluid is in satisfactory condition. But if the spot does not spread out and is dark in color, the ATF is oxidized and should be changed.