ATF: To Change Or Not To Change?
 

Hi all,

First post here, but I've been reading avidly for a little while now. Last weekend I acquired a '90 240 GL Estate with the auto 'box (presumably an AW-70). I am currently debating whether to begin changing the ATF or not; it certainly needs it since I don't think it's been done in 135k miles. It does smell burnt and is dark in colour.

Upon picking it up, I noticed it was low and topped up about 1L. The car took positively to this, with a much-reduced delay when engaging Drive or Reverse. Shifts are smooth, and I don't believe it's slipping? Certainly, the speed picks up okay across the board, although it does have a tendency to just sit around about 2k with the speed coming up smoothly, above 2k all is normal... Is this slipping? Kickdown works fine, no clunks shifting up or down.

So, the question: do I leave in the probably burnt ATF because it just works, or do I begin the process of gradually changing the fluid over? My planned method would be to drain 2L out of the oil return into a large drinks bottle and then replace it with 2L of fresh ATF, drive for 100-200 miles and repeat over time until it starts running considerably cleaner.

Thing is, I will need this car pretty much daily over summer, expecting to cover about 1500 miles by September. I'm currently thinking it's pretty much a 50/50 on whether changing the fluid would improve or degrade performance, although the fact that it responded positively to topping up is perhaps a good sign?

Sorry for the long post, but better to be thorough, right?

Cheers in advance,
Adam

In my experience (BW55) it is far better to change the ATF.

The easiest way is to pump 2-3 litres from the fill tube (get a small electric pump, they are not expensive) and refill via the same. 3 or 4 partial changes a few weeks apart should improve the gearbox.

Servicing the transmission with new filters is a pretty good idea (as well as cheap and easy) once you have most of the old stuff out. A service kit like this one was only about £20 (from memory):

https://i.imgur.com/5P3C7fRh.jpg

:-)

Why would you not change it?

At 135k and that age it’s past it’s design life and the fluid will be out of spec.

I would change the power steering fluid (you will be surprised how bad it is!), axle oil, coolant etc etc.

PS (to my post above): a small electric pump like this is good for removing ATF via the fill tube, and also from the PAS reservoir:

https://www.ebay.co.uk/itm/384741523...3ABFBMkOu5lK5g

... about a tenner.

Thanks for the pointers so far, it does seem like the consensus (both here and in previous threads across multiple sites) is to take it slowly with regular partial changes. Generally speaking, maintenance has been carried out on it (I have FSH with it), but just the ATF especially has been neglected, because 'lifetime' fluids, no doubt.

Othren, I do intend to change the filter and clean the pan etc. unfortunately, the lead times are all kinda long, so that'll probs have to wait until September. If anyone has any advice on the dipstick tube removal, that would be great (or should that go in a new thread?). Also, thanks for the link to the pump, looks pretty snazzy :)

I'll make a start in a bit and get a couple of litres out today (hopefully).

September would be a good timescale to change the filter and clean the pan. If you do partial changes in June, July and August you should have about 87% of the old ATF removed (not quite of course because heavier particles will tend to remain in the pan). If you change the filter then you won't contaminate it much at all.

:-)

Have you checked if the auto box has a sump bolt? My 87 AW70/1 has one and it's a doddle to drain 2500ml, refill, drive, repeat five or six times or until the 20l jug has gone. Every change brings back responsiveness to the box, even though the colour cleared up by the third change.

Advice about sump filter all good too, if a little more involved.

BicycleBoy, I'm almost certain mine does have a drain bolt but for now, I'm going to (attempt to) undo the return line at the radiator and drain it out into a measuring jug ~1L at a time, topping up after each litre, for two litres' worth. I know it's slow and inefficient, but it should be one of the easiest to do based on my current equipment. If it's properly seized on then it can wait, but unfortunately, I cannot afford to be stripping threads and stuff when I don't have a replacement bolt (let alone pan) and need the car daily for the next couple of months. I do appreciate what you're saying though, and agree that in theory, it's the simplest method :)

This scenario is very similar to changing the automatic fluid on early V70 & many other cars:~ (gradual change)

If you go for a larger supply (20L) of the appropriate oil from companies like:
https://www.smithandallan.com/
https://www.westwayoils.co.uk/
You can then take out some of the costs whilst choosing the correct specification for the car.
Trust it helps.
Bob.

Hope all of you are doing okay in this moment of temperature-related madness in the UK (36/37°C today, expected higher tomorrow). Just another quick update and I'm glad I have gone for it, still got 4L to go of my 12 originally purchased and I almost completely have 3rd gear hooking up as it should - tightening the kickdown cable a tad for slightly higher RPM shifts also seemed to help a little as well.

I believe my ATF was just incredibly dirty, as opposed to burnt, although it was pretty borderline as it definitely was slipping a little in third once up to temp prior to changing. In terms of a soft drink analogy: clean ATF = Vimto, my old ATF = Pepsi and then some (not sponsored, promise 😁).

Hopefully, the next 4L will continue to yield improvements. I would definitely recommend changing in 4L batches from the outset though, as a 2L change seems to get 'swamped out' by the old dirty stuff and doesn't yield much improvement at all. For future readers: it goes without saying though that you shouldn't attempt to drain out 4L of ATF in one go because that will make the transmission run dry. Drain 2L, refill 2L, drain 2L, refill 2L, etc.

Finally, for anyone intending to drain ATF via the radiator return fitting, a 12mm (approx 1/2" but a bit thinner) inner diameter length of hose is a perfect fit; the diameter of the fitting including threads is 12.3mm. I would recommend a 2m (approx 6') length to be an ideal amount.