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Old 17th October 2020, 13:35   #1
Londonsteve
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Default Recent new 75 CDT owner - autobox oil change

Hi all,



I bought my 75 CDT (not sure if it's an 'i' or not - first registered 07/03) about 6 weeks ago and it's a wonderful car. In fact, I'm kicking myself for not having bought one sooner! They've been so affordable for so long, I feel like I've missed out by jumping on a 17 year old car that has unfortunately led a hard life in recent years, but carefully maintained before that.



So far it has had a fair bit of work, starting with an oil and filter change, AC gas recharge during which time it was diagnosed that the electric cooling fan had failed, so the front end had to come off the car and I had one of Jules' fans fitted, while an intercooler hose and AC condenser was renewed at the same time. Jules kindly supplied some new intercooler seals which were replaced at the same time as the hose. The plenum chamber covers were removed, the chamber was vacuumed clean of debris and they confirmed there was no evidence of standing water having been there recently, although they didn't test the hoses or prod something in to poke them clean. Was this perhaps a mistake? Last but not least, it had a new bonnet alarm switch.



I procured 5 litres of genuine Land Rover ATF402 and we set about changing the autobox oil. My garage are Citroen and Peugeot specialists, working mainly on the rare classic and esoteric stuff. I've always had hydropneumatic Citroens of some description so they are my go-to garage and are very helpful.



They had never done the job before and checked on Autodata before starting. The gearbox wasn't misbehaving but at 101k miles, it had done a fair amount of mileage, I couldn't be sure when the gearbox oil was last replaced and I wasn't entirely happy with the shift quality. It would shudder slightly when first entering 'D', some degree of shudder was also tangible while holding the car stationary at the lights with the gearbox in Drive and the downshifts when slowing to a halt were not smooth, particularly when re-entering 1st gear. Changing up was fine and there was no flaring between gears or any serious misdemeanours.



With the box at ambient temperature, after a 15 mile drive to the garage but having had 20 minutes for the car to cool down, they opened the drain plug and precisely 4 litres of not excessively dark or malodorous oil came out. After replacing the drain plug, they put in precisely 4 litres of ATF402. Despite what Autodata was telling them, my box didn't appear to have a level plug on the side, so there was no way of telling if the old and new level were correct.



My understanding is the change process was correct, that 4 litres is the expected drain volume, thus indicating that the existing level was fine and I now have 50% diluted ATF in my box. I would be grateful if someone could please confirm that this is all correct and we didn't miss a step or make a big mistake, e.g. by not paying attention to the gearbox temperature, etc.



The oil change specified at 60,000 miles, does it include another 4 litre drain, to leave 75% fresh oil in the box? I struggle to imagine that every 60k miles the manufacturer only advises a 50% dilution. I have another 4 litres of new oil so I'm planning another 4 litre drain soon, unless an expert on here advises a different approach.



Many thanks for your time and expertise!
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Old 17th October 2020, 14:22   #2
Brunty
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My mechanic changed fluid and told me to come back after a week and do the same again, now smooth as new. He suggests changing it every 4 years.
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Old 17th October 2020, 16:13   #3
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A bit of reading for you which will have all the info you need. Do read it all as there are lots of useful bits re drain and level plugs, capacities etc.


https://www.the75andztclub.co.uk/for...d.php?t=124816
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Old 17th October 2020, 16:25   #4
Londonsteve
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Fantastic! As you write, everything needed, thank you!


Looks like we were on the right track with the first 4 litre drain but the oil cooler trick would have significantly increased the % of clean fluid in the box. Alas, now that the dirty and clean fluid has mixed, when doing another 4 litre drain and refill we might as well just using the simple drain plug solution, unless someone is willing to buy another 5 litres of oil to increase the dilution beyond the 75% clean oil it will be. I think I'll settle on 75% for now and follow the procedure at the next change.


Does anyone know what was the official dealer change procedure? 4 litres and be done with, or more like the process photographed, achieving maybe 85-90% fresh oil?



There SHOULD be a level plug on mine but we couldn't find it. Perhaps later CDTs came with a different spec and they deleted the level check as surplus to requirements? My mechanic is VERY thorough and diligent, I cannot believe he wouldn't have looked very carefully and only reported back the fact that I don't have a level plug if that is in fact the case. He was as surprised as I was.
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Old 17th October 2020, 16:28   #5
Londonsteve
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Quote:
Originally Posted by Brunty View Post
My mechanic changed fluid and told me to come back after a week and do the same again, now smooth as new. He suggests changing it every 4 years.

4 years sounds wise. That appears to be the advice too in the factory service checklist. 60k miles or 4 years.
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Old 17th October 2020, 16:57   #6
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Hello Steven and thanks for a very clearly written account. I particularly noticed your use of the specialist term "flaring".
Quote:
Originally Posted by Londonsteve View Post
... my box didn't appear to have a level plug on the side ...
That's correct because the level plug is on the bottom. It's at the base of a vertical tube inside the gearbox so that fluid ceases to flow and starts dripping when you've reached the right level.

A fluid temperature is specified and it's possible to detect it using the resistance reading of the sensor. However, before the arrival of computerised diagnostics the instructions were to measure the level with the gearbox at "normal working temperature". That method seemed to work satisfactorily for many decades so you need not worry unduly.
Quote:
Originally Posted by Londonsteve View Post
The oil change specified at 60,000 miles, does it include another 4 litre drain, to leave 75% fresh oil in the box? I struggle to imagine that every 60k miles the manufacturer only advises a 50% dilution.
Yes, obtaining a mix of half used and half new fluid at every change is how it's been since automatic transmissions were invented! If you now discard 50% of that mix and add an equal quantity of new fluid the 4 litres of 50:50 mixture is now combined with 4 litres of new fluid. What happens to the concentration of used fluid now? Whatever the answer, all 8 litres still contains a proportion of used fluid.

The link which roverbarmy has supplied gives Beinet1's method of replacing all 8 litres of ATF which is most likely the best solution.
Here's another slightly different procedure by Caskin.

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Last edited by SD1too; 17th October 2020 at 17:03..
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