1st round of fluid exchange (made simple?)

[Shel155]

02 S8. Please excuse the potentialy blasphemous nature of the post. Ready to do new filter and fluid exchange. Could I not... for first round, when good and cold and the fluid is not expanded, merely drain whatever drains, measure precicely, and replace that? Then a day or so later do it right? Trans is running perfectly right now, but it's pretty brown looking. Thanks

[spannerrash]

The problem is, you will not be able to put back the same amount as you take out without running the car. If you get 5 litres out you will only get 3 litres ish back in.

If what you mean is to take out the 5 litres ish whilst cold, replace the 3 litres and then start the car and replace the other 2 litres? It's a bit rough but it should be no worse than it already may be. By that I mean if it's low on oil now, then it will still be low on oil afterwards.

If you in intend to do it correctly in a couple of days, why not just do it correctly now. The only thing I can guess is that you want to run around in it for a couple of days to circulate the new oil. I personally don't think it's necessary to drive the car to achieve this. Simply running the engine / gearbox whilst stood still will circulate the oil.

Make sure you do your research before attempting this. It's a high risk procedure if you get it wrong.

[The_Laird]

It really is a high risk DIY procedure! Some succeed, and some leave well alone, but the DIY approach can lead to the crud being disturbed and circulated, resulting in a shot gearbox. If you plan on making the car a ‘keeper’, take it to Mackies in Glasgow for a proper gearbox service.

[spannerrash]

100% agree with the Laird. Do your research and plenty of it. A tired old box with high milage and a poor service record could suffer if given too aggressive an oil change.

There is nothing wrong with changing fluid regularly on a good clean box, it will keep it that way. But as the laird has said, changing the oil on a box with a ropy service history may do more harm than good. The fresh detergents may free up crud that may then circulate and cause other problems. Some owners have claimed "clutch slip" after an oil change on an old un-serviced box.

It's a controversial subject. This is one of those rare examples of where you could kill a car with kindness.

I can't emphasise enough. Do your research before going forward. Learn from what others have experienced. This is a D2 killer if it goes wrong.

[Shel155]

I was overlooking that it has to be running to refill, I'll heed the warnings on the short-cut, thank you. Bout the fluid, yes have read the pros and cons (and the tragic outcomes), the fluid is nothing like some I've seen as far as grunge so I'm pretty sure it's been serviced before. If it kills it then it kills it but I had one kind of hard shift today which makes me think I should be dropping the valve body, cleaning it and probably replacing at least that one valve with the modified "no ream" version. Don't worry so much "I got this" Btw I'm in WA state US, Scotland sounds nice tho. Haha, I can imagine you guy's rolling your eyes at me, really it'll be fine and if not, I'll fess up- waiting for parts.

[MikkiJayne]

I tried the 'if it ain't broke don't fix it' approach with one of mine and it broke anyway

Personally I am sceptical of the dislodged crud theory as all the auto boxes I've opened up have been spotless inside. I suspect it is more to do with running the box low on oil on startup, which is inevitable due to the stupid filling procedure. A gearbox which is just on the limit of working properly could be tipped over the edge by running short on oil for the minutes it takes to top it up. I have no solid evidence for either theory though. Just that all 5HPs will fail eventually whether you service them or not, and servicing may or may not shorten or extend their life.

However, as the guys have said, this is not something to be bodged or short-cut because if you get it wrong (even to the tune of a litre or so) you're pretty much guaranteed to break it. The converter is first to suffer from low fluid and it'll burn out its lockup clutch. Next is the oil pump, which will cavitate on hard acceleration or corners. Cavitation leads to metal fragments being circulated through the valve body and clutch cylinders and then its all over. If the pump survives but the clutch cylinders can't get full travel, and the clutch packs are already worn, then the clutches start slipping and burn out.

Side note - don't believe the Wheeler Dealers episode where they magically fixed a broken Porsche Boxster 5HP19 gearbox by doing an oil change! Not only did Edd show an incorrect filling procedure (the engine wasn't running because it messed up the audio), but no 5HP in recorded history has been fixed with fresh oil. I guarantee they put a replacement gearbox in that one and glossed over it because it meant Mike's imaginary profit went up in smoke

Do it properly or don't do it at all

Edit - I took too long writing that! Hard shifts can also be caused by the MAF failing. Check the engine load at idle fully up to temperature with accessories off. Should be no more than 16-17%. Above 20 means a bad MAF. If you're in the US then at least its easy enough to get the Transgo kit and possibly a rebuilt gearbox if it does go bang.

[tintin]

Originally Posted by The_Laird

It really is a high risk DIY procedure! Some succeed, and some leave well alone, but the DIY approach can lead to the crud being disturbed and circulated, resulting in a shot gearbox. If you plan on making the car a ‘keeper’, take it to Mackies in Glasgow for a proper gearbox service.

This.

I took my S8 to another "reputable" service outlet for this, and they still managed to make it worse. So only Mackies for me too, even though it's a 500 mile round trip - an essential preventative investment.

[spannerrash]

When I did mine last year I replaced the front lower valve body. Got Nat Wentworth (think that's right) at Ericssons in the US to make up a full unit with new parts and housing for me. If you're in there anyway it's a fairly simple unit to swap. I haven't noticed any difference in operation at all but having a new housing and updated pressure regulator valve makes me feel I've done my best.

These boxes do have multiple failure modes though so I've only addressed one of them. Fingers crossed.

[spannerrash]

This may seem a little left field but IIRC someone on this forum has filled there gearbox via the oil cooler pipe at the radiator. It may allow you to get the extra 2 litres in without having to run the engine. I will be giving it a try the next time I do mine. It may help with the initial low oil issue when first starting the car after putting the first 3 litres in.

[MikkiJayne]

I've replaced the 250ml of oil which is lost from the heat exchanger when removing the radiator that way, but I haven't tried filling it. I don't believe there is a free-flowing path in to the sump from either of those ports as I think they are between the pump and the valve body, although that is something I have always meant to investigate.