Discovery Transmission Oil

[repton]

Whilst towing a trailer of about 2.5 tons up a longish steepish hill yesterday a red light came on just above the engine temperature gauge which, going by what it looked like I assume was telling me that the ATF was getting a bit too hot in the autobox.

Assuming I'm right about what it meant, are there some servicing type things I can do to help keep the temperature down (fresh ATF? is there a filter?) or do I need to consider fitting a bigger oil cooler for it? The old Disco never did it but I never towed anything quite that heavy with it. The problem I guess in part is that on the roads around here you never get it into lockup with a trailer on (especially when it has two horses in it) and so the 'box is working hard the whole time.

TIA,
Paul

[Bo]

There is a filter in the gearbox that can get overlooked. If you have cooked the oil it will need to be changed so do the filter at the same time. The filter is located within the sump of the auto box. It's not complicated but make sure you get a new seal for the sump before starting just in case.

[repton]

The light was only on for about 30s as it came on just as we crested a hill so hopefully I haven't cooked the ATF but I will plan to change it (and the filter) in the near future as I've no idea when it was last done so it could already have been cooked by someone else.

Ta,
Paul

[dave willard]

The light was only on for about 30s as it came on just as we crested a hill so hopefully I haven't cooked the ATF but I will plan to change it (and the filter) in the near future as I've no idea when it was last done so it could already have been cooked by someone else.

Ta,
Paul

Hi
When you change the oil you will not be able to remove all of it as some will stay in the TQ
I suggest you change the oil, run it for a few miles then drain remove the sump (note you may need to remove a mounting to do this)
I suggest a new mesh filter but you can clean the old one, on mine the screws holding the filter in place were tight may have been sealed in, they rounded off so I had to find replacements so make sure you have a well fitting driver on these screws you may want to use locktight when putting back the filter, problems if they come loose
I held the rubber gasget in place with a little grease but it should be a self holding fit.
Fill with oil then select all gears several times to fill up as per the manual.

I know that changing the oil twice costs more but it is worth it

I seem to have read in a manual that when in slow moving traffic selecting low box if the temp light comes on

I used low box when going up a hills in hot weather with a heavy trailer as this helps to prevent heat being generated in the auto box also lock up occures at a much lower speed which keeps the heat down & gives more power to the wheels
You could also select a lower gear as this means the TQ not working so hard
My problems were not heat from the auto box but the engine getting warm, I did have a digital readout of the engine block temp

I also put in a switch to manually turn on the fans as the auto one switches on when the engine starts to get quite hot, switching on earlier keeps it cooler
Does yours have aircon if not the above may not apply

Suggest you also look at the autobox oil cooler is it clean to allow it to dissipate heat

If you have aircon clean the radiators as there will be one in front of the engine cooling one which restricts air flow

Have fun D

[davew]

There is a school of thought that the last thing you want to do, particularly with a high mileage box, is change the oil and filter. As the clutch plates wear they cause a build up of sludge in the gearbox and by flushing the oil all you end up doing is encouraging the sludge to migrate to the valve block where it causes more issues.
I seem to remember there being an article about this on the Ashcroft web site as many people were changing the oil in the hope it would improve things and it was actually making things worse.
Not for the squeamish but I believe disconnecting one side of the oil cooler and running the engine is a very good way of emptying the gearbox. I've done it as a result of pipe failures in the past but I know of at least 2 garages that do it as a way of getting as much oil out as possible. Obviously don't run it for very long and don't rev the engine !
Anyway, it sounds like your gearbox got a bit warm, probably nothing to worry about but a bigger or additional oil cooler might be a worthwhile investment if you're towing regularly. You can never over cool an auto.
As well as low box you can also reduce the temperature by locking the box down into a suitable gear, particularly if it's "hunting" for the right gear.

[repton]

Thanks for the replies, I'll pass the comments about low box / locking down a gear to Lindsey as the heavy trailer in question is our horse trailer which comes in at around 2500kg with both our horses in it.

Regarding fitting a bigger oil cooler - is there an easy drop in replacement cooler I can source? It'll be doing quite a lot of towing so given DaveW's comments about it being impossible to overcool an autobox I figure it would be sensible to fit a bigger one if I can do so without breaking the bank.

On the subject of sludge in the gearbox (as mentioned by DaveW) if I take the sump off to change the filter will I not be able to clean that out? Is the theory still valid if you're doing the filter too rather than just doing an ATF change?

Ta,
Paul

[Matthews]

It's the sludge build up in the valve block and upper case galleries that cause the problem , once disturbed they can block the valves , as far as removing the oil filter it uses T27 torx head bolts not the more common T25 in most kits (the T25 will work but if the bolts are tight then you can strip them , this is why I have a t27 bought separately !).
Matthew

[repton]

I've decided to take the risk and change the fluid. I'll do the fluid once, and then do it again in a month or two and do the filter at the same time (having noted Matthew's point about the T-27 bit required).

So next question - what fluid do I need? The manual says "Dextron IID" but everything I can find seems to be different to that.

Here are two different ones from Millers with quite different prices:

Firstly, at £20.70 for 5l:
http://www.ebay.co.uk/itm/150981525509

Or at £29.99 for 5l:
http://www.ebay.co.uk/itm/171232694798

The first one says it's "Dexron IIIH", the second "Dexron III". From the description it looks like the cheaper one is part synthetic, the dearer fully synthetic.

I assume these would both be OK, with the fully synthetic one being a better bet?

TIA,
Paul

[Matthews]

As long as it's Dexron either 2 or 3 in any variety, just not the Ford whatever it is spec . I run 3 in the disco and 2 in the 90 (will put 3 in the 90 if I ever have to change it ).

[mpblandrover]

http://m.ebay.co.uk/itm/300896904723