Aisin Gearbox cooler problem

[heshamderbala]

Hi
I have Citroen c4 Grand Picasso 2015 automatic 6 speed petrol new shape and i have problem happend that the car temperature got very high and got a warning to stop the engine and after that i went to the service center and they told me that the gearbox cooler is damaged and needs to be changed until that point it is ok but they told me they have to change the gearbox oil for 3 or 4 times to clear any effect of the water that have been interchanged with gearbox oil and i did this for 3 times and everytime the oil comes out mixed with water then they told me you have to change the gearbox as they cant do this forever .My question is this normal that a car heats we change gearbox is that normal i need someone to convince me that this is normal and could happend in any other car
Thanks

[GiveMeABreak]

It can and does happen. If the oil cooler fails coolant will get in and will destroy the gearbox if not repaired immediately - but it will depend on the amount of contamination and how long it was driven in this state before you noticed.

Here is a recent example from another member that has had this happen on his C6:

https://www.frenchcarforum.co.uk/forum/ ... 76#p625376

If you can thoroughly flush it out then great, but if not, the water will react with the various metals and cause rapid deterioration of the components. This will likely lead to premature failure of the box and will need a replacement or a rebuild.

As you are in a very hot country, this has caused the oil cooler to fail sooner.

Unfortunately in the case of the other member (Davis), even after flushing it through, the gearbox failed after a 100 miles, if you read through.

[heshamderbala]

Hi
So every time i got the alarm of overheat i have to know that i will change the gearbox.
I think this is something strange why they do that way of cooling of gearbox like this is that for the sake of not to change gearbox oil liftime i think it will be better to change the oil like many cars than going to a hell scenario of changing gearbox.
I mean to prevent that way of cooling of oil or all of the cars have that way to cool the gearbox oil i dont know but iam seeing that that way is endless specially when you know the reason of fault was the thermostat joint or elbow i dont know its meaning in english as this is the main problem from the begining

[GiveMeABreak]

It is well-known amongst AM6 and other Aisin owners that there is no such thing as 'sealed for life'

We recommend the gearbox oil is part-changed (as you can't drain the torque converter fully) as part of your servicing schedule, as this will help remove burnt oil and contaminants and prolong the life of the gearbox. In hotter countries this really should be done due to the additional heat generated and stresses on the system.

It might be that your oil cooler has failed internally - this can happen in addition, regardless of how often you change the gearbox oil unfortunately.

[white exec]

The oil (transmission fluid) heat exchanger has two pathways through it - fluid and coolant - and they should be separated, and not mix. If corrosion happens inside it, even a small pinhole - it can allow very hot gearbox oil to be injected into the cooling system, or coolant to find its way into the gearbox.

The heat exchanger (oil cooler) can be easily tested on its own, to check whether it has failed.
It will need removing (central bolt and the coolant hoses), and then pressure testing on the bench.

One other way to check it (on the car) is to clamp the two coolant hoses so they won't leak, and then remove them. If the engine/gearbox is then run, if there is an internal leak you should find gearbox oil coming out of one or both of the aluminium coolant pipe connections. It may only come out slowly, if the internal leak is very small.

If in doubt, just replace the cooler. It seems they don't all last for ever.

Gearbox replacement (or a rebuild) should only be necessary if lasting damage has been done by coolant getting into the gearbox. Several posts here describe what is necessary to flush out contaminated fluid.

You are right to say that these devices are not a foolproof and longterm-guaranteed way to cool the gearbox fluid.

It is essential with these aluminium components that a good quality coolant of the correct type is used, and is regularly renewed according to instructions - even if the car is used where there is little chance of frost or freezing conditions. Coolant is not just an anti-freeze, but contains very important anti-corrosion additives to protect the mixed-metal parts of the cooling system.