Hi, I have a 2003 RR HSE, 4.4L & 5 Spd ZF Auto. Several times when towing the boat , the trans seems to get hot & "derates". It will change down to 3rd , & not change up. Changing to manual/sport mode doesn't help. Do l need a Trans cooler or should I get it flushed ? It has done about 103,000kms
Any help/advice appreciated
Thanks

The bottom of the radiator which I believe operates the transmission cooler is known to get blocked up with sludge and debris. Either flush your radiator or get a new one. The oil cooler could also be the culprit ?

Check any service history for new parts but unless they have been changed recently you need a new radiator and transmission cooler as they get blocked,you also need transmission oil as it deteriorates.there is plenty of info on this site about it .

As both people said before, new radiator and gearbox cooler.

If you keep running the gearbox hot it will be damaged and you will need your gearbox reconditioned.

Make sure you get the gearbox oil changed at the same time 2003 Range Rover 4.4 Litre V8 - Adriatic blue

2003 Range Rover 4.4 Litre V8 -Maintenance History Click Here = http://www.fullfatrr.com/forum/topic39687.html

Within the plastic manifold that the gearbox oil cooler attaches (which is on the left hand side of the main radiator when viewed looking into the engine bay) is a separate thermostat for the oil cooler, this can get blocked of break as well so it's best to change the whole lot, also the oil cooler pipes back to the transmission can delaminate and collapse preventing the oil from getting cooled.. If you can afford it it's best to change the lot, if not, take it all out and give it a good looking at and cleaning. It is virtually impossible to clean out the main engine radiator or oil cooler well enough to make any difference...

To sort the issue completely change

Main engine radiator (check and replace all hoses if the are at all hard or the plastic has gone from black to brown)
Oil cooler radiator
Manifold and thermostat
Oil cooler pipes.
Coolant
Transmission oil (the correct fluid, not generic stuff)

Then fit the cooler thermostat modification.

http://www.fullfatrr.com/forum/topic39362.html

Job done...  Pete
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Goodbloke1 wrote:

Hi, I have a 2003 RR HSE, 4.4L & 5 Spd ZF Auto. Several times when towing the boat , the trans seems to get hot & "derates". It will change down to 3rd , & not change up. Changing to manual/sport mode doesn't help. Do l need a Trans cooler or should I get it flushed ? It has done about 103,000kms
Any help/advice appreciated
Thanks