MG4 Reduction Gearbox Oil Leak

[troopercooper]

The leak is caused by the large crown gear throwing oil directly at the breather to such an extent that it leaks out of the breather. In theory reducing the amount of oil may reduce the amount that leaks out , but the reality is that if the crown gear is still sitting in oil then it will throw this oil into the breather because the breather is in direct line of the oil throw. So there would have to be very little oil left in for the leaking to stop completely. If the level got that low then the gears would not have enough lubrication as there would not be enough oil throw to lubricate everywhere. I wouldn't be happy to do lots of miles in this situation. Hopefully no one will suffer gearbox problems.

Thats really interesting to hear directly what the issue is. Do you know if this is therefore the case on all models up to now? Is it a defective, missing part or perhaps an isolated moulding error etc? Thanks

 

[Deleted member 10041]

The leak is caused by the large crown gear throwing oil directly at the breather to such an extent that it leaks out of the breather. In theory reducing the amount of oil may reduce the amount that leaks out , but the reality is that if the crown gear is still sitting in oil then it will throw this oil into the breather because the breather is in direct line of the oil throw. So there would have to be very little oil left in for the leaking to stop completely. If the level got that low then the gears would not have enough lubrication as there would not be enough oil throw to lubricate everywhere. I wouldn't be happy to do lots of miles in this situation. Hopefully no one will suffer gearbox problems.

I wonder how long/much before it got to a level that was detrimental to the gear box

 

[AndyL61]

Thats really interesting to hear directly what the issue is. Do you know if this is therefore the case on all models up to now? Is it a defective, missing part or perhaps an isolated moulding error etc? Thanks

It's the basic design, a breather is only to allow for air expansion due to temperature increase, oil should not go into the breather. So either move the breather or fit an internal baffle plate to stop the oil entering the breather. The modified breather is very much a belt and braces fix which simply holds the oil in the swan neck pipe then allows it to flow back into the casing when you stop. It's not an ideal fix but better than nothing.

 

[Cocijo]

I don’t think the discharge has that much to do with oil level too high - up to a point.
The breather is there to prevent pressure build up. If the breather does not do its job properly the pressure will push out oil - usually after a run.
This may be why we are seeing oil discharged after the car is used on a decent run but ok on shorter stints.
Of course if there’s less oil under pressure it might not leak as much or at all. But risks then are it not lubricating as it should.
Perhaps the modification stops pressure build up. All speculation….
It would be great to get an honest answer from MG
Most owners will accept an issue as long as they are told the truth and it is actively put right.

 

[StackH]

It would be great to get an honest answer from MG
Most owners will accept an issue as long as they are told the truth and it is actively put right.

And this, for me, is the crux of it and why I cancelled my order. These days, with internet forums, many more owners talk with each other (virtually, anyway) so the issues are well known. For MG to fail to acknowledge and advise on them, even when a fix is available, is poor customer service. And to simply direct you to your dealer, when different dealers are spinning different stories (I suspect because MG doesn’t tell them either), is even worse.

 

[AndyL61]

I don’t think the discharge has that much to do with oil level too high - up to a point.
The breather is there to prevent pressure build up. If the breather does not do its job properly the pressure will push out oil - usually after a run.
This may be why we are seeing oil discharged after the car is used on a decent run but ok on shorter stints.
Of course if there’s less oil under pressure it might not leak as much or at all. But risks then are it not lubricating as it should.
Perhaps the modification stops pressure build up. All speculation….
It would be great to get an honest answer from MG
Most owners will accept an issue as long as they are told the truth and it is actively put right.

The oil should not be under any pressure. The job of the breather is to do just that , allow the cavity to "breath" to atmosphere to eliminate any pressure. The breather should not have oil directly thrown at it to the extent that the oil leaks to atmosphere. That is the problem. The amount of oil should be the level that the designer deems enough to provide ample lubrication when said oil is being thrown around the cavity during high speed and sustained use. If this oil amount is reduced too much then wear and heat is increased. Hopefully this won't be the case .

 

[WalkingBootWeather]

I think @AndyL61 gives a good explanation that tallies with my understanding, This is Boyle's Law at play. If there wasn't a way to relieve pressure then undue pressure would be applied to seals etc. The new breather is a bit of a bodge but should work by capturing oil thrown outwards and allowing it to return to the chamber rather than be lost to the system.

Speculation on my part, but the ultimate solution is a redesign with internal baffle and/or a relocation of the breather, but as I say the new breather will likely provide acceptable results. Without it I anticipate that EVERY MG4 will eventually leak when driven harder (if sufficient oil to lubricate is in place), or the transmission will fail due to insufficient lubrication.

Many cars have similar design defects that compromise reliability and life of components. Good engineers recognise issues and continuously improve designs.

The correct action IMHO is to fit new breathers to ALL vehicles until such time the component can be redesigned (model refresh?).

In the short term I doubt there would be damage in driving without the new breather but I'd strongly advise all owners without the new breather to monitor the situation and speak to dealer as soon as a leak is identified.

 

[Alb]

This stuff has all been explained before but I suppose I can forgive anyone for not feeling up to reading all 1820 (and counting) posts

 

[Xiao Wazi]

I'm watching this thread with interest as my plan was to replace my current 2018 ZS SUV with an MG4 however there seems to be so many issues with the design of the car.

I am old enough to remember with the issue that affected the original Austin Mini Metro 3 door version were the petrol filler was placed in front of the off-side rear wheel.

Sometimes if you had a full tank of petrol in the tank, after driving around performing right handed turns, some of it would be forced out of the fuel cap and go all over your rear off-side wheel causing your car to spin around.

It was said at the time that Austin Rover blamed the owners for not securing the petrol caps on properly but then the British media somehow got involved.

Austin Rover finally fixed the issue by locating the fuel cap higher up the body but as the late Sir Winston Churchill once said, “Those that fail to learn from history are doomed to repeat it.”

 

[AndyL61]

This stuff has all been explained before but I suppose I can forgive anyone for not feeling up to reading all 1820 (and counting) posts

Yes you're right we should not be still posting about this because it should have been put right by now.

 

[Deleted member 10041]

I'm watching this thread with interest as my plan was to replace my current 2018 ZS SUV with an MG4 however there seems to be so many issues with the design of the car.

I am old enough to remember with the issue that affected the original Austin Mini Metro 3 door version were the petrol filler was placed in front of the off-side rear wheel.

Sometimes if you had a full tank of petrol in the tank, after driving around performing right handed turns, some of it would be forced out of the fuel cap and go all over your rear off-side wheel causing your car to spin around.

View attachment 14161

It was said at the time that Austin Rover blamed the owners for not securing the petrol caps on properly but then the British media somehow got involved.

Austin Rover finally fixed the issue by locating the fuel cap higher up the body but as the late Sir Winston Churchill once said, “Those that fail to learn from history are doomed to repeat it.”

View attachment 14162

It's almost like history has repeated itself

 

[Xiao Wazi]

It should be said that the number 4 in Mandarin Chinese sounds similar to the sound for death. I hope that the on-going problems with the MG4 isn't going to cause MG Motor UK too much negativity. It also explains why the MG4 sold in China is called the Mulan as no one would like a "death car".

It's almost like history has repeated itself

It is strange that SAIC's MG Motor UK have nothing to do with Austin Rover yet the same pig-headed mentality seems to exist. <shrug>

 

[troopercooper]

It's the basic design, a breather is only to allow for air expansion due to temperature increase, oil should not go into the breather. So either move the breather or fit an internal baffle plate to stop the oil entering the breather. The modified breather is very much a belt and braces fix which simply holds the oil in the swan neck pipe then allows it to flow back into the casing when you stop. It's not an ideal fix but better than nothing.

What confuses me though is that if that is the case, surely this has been apparent from the very start and affects every model released?

 

[Deleted member 10041]

I think it has a lot to do with type of journey speed, length, distance at a guess anyway

 

[Ste]

These instances of dealers telling blatant lies are a disgrace.

Had a thought with regards the oil leak,

how fast/much do we think is leaking out?

It obviously manifests its self when driving then continues to drip from the tray when stationary on the drive.

I'm just curious because there is not a lot of oil in there to begin with (900mls)

Has anyone got to the stage where they had the leak and it stopped prior to taking it in to get the new breather fitted.?

Basically what I'm getting at is how much does it have to lose for it to stop/if it stops?

And how much of the 900mls (that the manual says should be in there) would it need to drop to before it could potentially be detrimental to the gear box?

I’ve been thinking the same??? So today I cleaned it all up, done a 40 mile round trip and nothing from leaving to stand??? See if anything’s dripped on the cardboard I placed underneath. My had oil leak from about 70miles from new.

 

[domsim]

I took the car to the dealer today to have the oil leak triaged, along with a chirruping air con compressor.

Speaking to the technician, he was saying that they needed to see it and send the details to MG because there are three different kits to resolve the oil leak so they need to make sure they’re getting the right one.

They’ve just called me back (he seemed surprised that MG had responded so quickly). The new part/kit should be with them in seven to 10 days.

For the aircon, MG have suggested a regas as a first step - worth a shot.

So far, the dealer and MG seem to have been responsive and I’m still loving driving the car.

The balance is definitely still in favour of the car being great but having some resolvable issues thus far.

 

[Ian Key]

For the aircon, MG have suggested a regas as a first step - worth a shot.

It's possible as the gas is also a lubricant which is why if the aircon isn't serviced regularly it can cause the condenser to rust from the inside and the o rings to dry out. Voice of experience and it cost Available Car several hundred pounds on a car I bought off them.

 

[Davemac278]

I took the car to the dealer today to have the oil leak triaged, along with a chirruping air con compressor.

Speaking to the technician, he was saying that they needed to see it and send the details to MG because there are three different kits to resolve the oil leak so they need to make sure they’re getting the right one.

They’ve just called me back (he seemed surprised that MG had responded so quickly). The new part/kit should be with them in seven to 10 days.

For the aircon, MG have suggested a regas as a first step - worth a shot.

So far, the dealer and MG seem to have been responsive and I’m still loving driving the car.

The balance is definitely still in favour of the car being great but having some resolvable issues thus far.

That's interesting as I have not heard of there being more than one style modified breather. I sent photos of leak to dealer and part ordered today. Told MG have them in stock in UK so hopefully dealer will get next day or so but sent out via Royal Mail.

 

[Cocijo]

Strange looking design.

 

[Deleted member 10041]

Bit of hose, bend it in the middle to stop the oil reaching the breather valve, big brackets to bolt it on, hardly anything to it to be fair, it does seem to work though