MG4 Reduction Gearbox Oil Leak

[Deleted member 9909]

Manual gearboxes in the past did not need coolant, they were air cooled via external fins. Cannot comment on more modern manual transmissions. Automatics are different kettle of fish due to torque converter creating excess heat I believe, so the MG4 transmission coolant makes sense given it handles the torque?

 

[Cocijo]

Manual gearboxes in the past did not need coolant, they were air cooled via external fins. Cannot comment on more modern manual transmissions. Automatics are different kettle of fish due to torque converter creating excess heat I believe, so the MG4 transmission coolant makes sense given it handles the torque?

I’m not sure. Plenty of ICE produce more torque. Plus it’s not an automatic either obviously - it works more like a final drive assembly. It must need cooling though otherwise it wouldn’t be there. Still not sure why though.

 

[Deleted member 9909]

I was under the impression that the reduction gearbox manages the torque, which I would imagine creates heat similar to an automatic torque converter, was the assumption I was making. Apologies if I am getting this wrong as I am no expert on this subject matter but it opens the door re is the coolant system doing a good job at managing the heat?

 

[Cocijo]

I don’t know how efficient cooling is on the MG.
A conventional torque converter on a ICE uses a fluid flywheel type arrangement that manages the rotational output from the engine and transfers (and torque multiplies) this to the gearbox. This can create quite a lot of heat.
These torque converter type gearboxes come in various forms.
Another popular automatic gearbox is a twin clutch gearbox that works differently again to the epicyclic type gearbox. This does not need a conventional torque converter.
A transfer box and differential gears work much the same as an axle or final drive do. Transferring and reducing the gearing of the power produced from the electric motor through the differential and out to the road wheels via the drive shafts. Because of the way the electric motor produces power only one fixed reduction gear is normally needed.

 

[Hagen]

I’ve never seen a passenger vehicle ICE with a liquid cooled gearbox/axle - I wonder why EV‘s need it? Also in some ICE vehicles the gears are very close to a hot engine blo

Indeed, although all it would really need is an expansion bottle type arrangement at the top, perhaps with the breather valve mounted on top of that, so that wouldn't be expensive at all.

Perhaps something like this at £12 with the original ball-valve breather cap fitted into the lid?

As a note, it wouldn’t need to be anything like this big as the amount of oil at any one time is small, it just makes a mess over time.

Its a good idea for cooling fluid that is expanding. I guess that MG4 has somewhere in the liquid cooling system, an expansion bottle. However the oil in the gearbox has 1 function only: lubrication. It can only do that job well, when it stays in the gearbox. I think MG is facing a serious problem with the leaking gearbox. I sincerely hope that they find a solution otherwise there 'winner' car changes maybe to a 'loser' car.

 

[WigglePig]

Its a good idea for cooling fluid that is expanding. I guess that MG4 has somewhere in the liquid cooling system, an expansion bottle. However the oil in the gearbox has 1 function only: lubrication. It can only do that job well, when it stays in the gearbox. I think MG is facing a serious problem with the leaking gearbox. I sincerely hope that they find a solution otherwise there 'winner' car changes maybe to a 'loser' car.

Let me be clear...every gearbox with a breather tends to lose oil very slowly, either as a mist or sometimes as small droplets. The 4 is no different in that regard but the design and layout means that it ejects more than would be desirable. Many gearboxes use an expansion vessel of some type to counter exactly the same issue. This is not a massive technical issue but has been handled very poorly by MG themselves; the dealer issues noted are common across many brand dealers and are not MG-specific.

The amount of oil a 4 'box pushes out is very small but it happens consistently over time. With an expansion vessel this will retain the few ml that get pushed through and it will drain back into the box as everything cools again. You would not end up with 200ml in the expansion bottle and insufficient in the 'box...the worst likely would be a few ml until the 'box starts to cool again, then it would drain back.

 

[Macadoodle]

The MG4 is liquid cooled (see page 321 in the owners manual), however it works somehow not good enough for the gearbox? View attachment 15316When the oil in the gearbox is warming up, then its expands. Therefore the air in the box escapes via the breather. Obvious it isn't normal that also the oil escapes via the breather. The only reason I can think of: the oil is getting too hot, despite the liquid cooling.

I'm 99% sure the reduction gearbox is not water cooled. The 5.6 litre circuit comprises motor, inverter, charger. Runs through the lower under the hood reservoir and the main radiator.

Battery and battery heater are exclusively on the 4 litre circuit, runs through the higher coolant reservoir and down to an evap heat exchanger unit in the air con circuit .
I think the use of 'electric drive transmission coolant' was just to keep it simple, they weren't literally meaning the transmission or gearbox.

 

[Deleted member 10041]

Let me be clear...every gearbox with a breather tends to lose oil very slowly, either as a mist or sometimes as small droplets. The 4 is no different in that regard but the design and layout means that it ejects more than would be desirable. Many gearboxes use an expansion vessel of some type to counter exactly the same issue. This is not a massive technical issue but has been handled very poorly by MG themselves; the dealer issues noted are common across many brand dealers and are not MG-specific.

The amount of oil a 4 'box pushes out is very small but it happens consistently over time. With an expansion vessel this will retain the few ml that get pushed through and it will drain back into the box as everything cools again. You would not end up with 200ml in the expansion bottle and insufficient in the 'box...the worst likely would be a few ml until the 'box starts to cool again, then it would drain back.

To be fair there are instances of members losing 300mls of the original 900mls. The picture macadoodle posted of the colour of his oil after 7 weeks proves there is a fair bit of heat going on in there.
As has been said it's just poor design and longer faster journeys certainly seem to bring it on.
As far as dealer/MG experience goes I can honestly say I have never had as poor service as some members have experienced and nobody has posted a positive MG customer service interaction

 

[AndyL61]

To be fair there are instances of members losing 300mls of the original 900mls. The picture macadoodle posted of the colour of his oil after 7 weeks proves there is a fair bit of heat going on in there.
As has been said it's just poor design and longer faster journeys certainly seem to bring it on.
As far as dealer/MG experience goes I can honestly say I have never had as poor service as some members have experienced and nobody has posted a positive MG customer service interaction

That's because they c##ked it up but don't want to say they c##ked it up and are desperately trying to play it down , hoping bodge will fix it , hoping less oil will fix it . Instead of fixing the design c##k up they made in the first place.

 

[Macadoodle]

I've just noticed the MG 5 gear oil motor specs seem to be the same as the 4's, 900ml of Shell SL2808.
Is this actually the same unit, repurposed for the RWD 4 ?? Would make perfect sense from an economies of scale perspective.
If it is, it just proves that the advice to reduce the oil volume to 750ml is a total panic measure.
Space in the FWD application to install a breather of a decent length is maybe the only difference?

Anyone with access to a 5 care to have a poke around ?

 

[Eber]

The amount of oil a 4 'box pushes out is very small but it happens consistently over time. With an expansion vessel this will retain the few ml that get pushed through and it will drain back into the box as everything cools again. You would not end up with 200ml in the expansion bottle and insufficient in the 'box...the worst likely would be a few ml until the 'box starts to cool again, then it would drain back.

Mmmh, I wouldn't call a completely soaked undertray or puddles on the driveway "small". And I'm not talking about my specific vehicle only, those pictures and videos can be found all over the net - many in this thread alone.

 

[Macadoodle]

Mmmh, I wouldn't call a completely soaked undertray or puddles on the driveway "small". And I'm not talking about my specific vehicle only, those pictures and videos can be found all over the net - many in this thread alone.

With the factory breather it seems to eject 300ml before slowing to the point of not being noticeable.
That's pretty much a full can of coke. Small wonder it makes such a mess on the car and parking spots

 

[Ayoull]

Mmmh, I wouldn't call a completely soaked undertray or puddles on the driveway "small". And I'm not talking about my specific vehicle only, those pictures and videos can be found all over the net - many in this thread alone.

I think you misinterpreting what is said.

Essentially it is being said the amount lost at any point in time is small but as it is happening on a regular basis it amounts to a larger problem.

That's what is being said by "small"

 

[Eber]

I think you misinterpreting what is said.

Essentially it is being said the amount lost at any point in time is small but as it is happening on a regular basis it amounts to a larger problem.

That's what is being said by "small"

Alright, I got that wrong then, sorry!

With the factory breather it seems to eject 300ml before slowing to the point of not being noticeable.
That's pretty much a full can of coke. Small wonder it makes such a mess on the car and parking spots

Is it really agreed upon that it does stop leaking below a certain filling level? Mine never did. It's a real shame I forgot to ask the dealer how much oil was left in there.

 

[AndyL61]

Alright, I got that wrong then, sorry!


Is it really agreed upon that it does stop leaking below a certain filling level? Mine never did. It's a real shame I forgot to ask the dealer how much oil was left in there.

It is my guess that because the oil is being thrown at the breather by the main crown gear then in theory it will keep doing this until the crown gear is no longer picking up oil . But obviously it will not throw as much as the level drops. It could get to very low level indeed but hopefully not to catastrophic level.

 

[Macadoodle]

It is my guess that because the oil is being thrown at the breather by the main crown gear then in theory it will keep doing this until the crown gear is no longer picking up oil . But obviously it will not throw as much as the level drops. It could get to very low level indeed but hopefully not to catastrophic level.

The breather does have ball bearing in its 4mm tube, it lifts in response to pressure from the box, exposing a little slot in the tube.
I guess at some point gravity pushing down on the ball will be greater than the pressure of oil pushing up.
At what point we get to this is anyone's guess

 

[WigglePig]

I think you misinterpreting what is said.

Essentially it is being said the amount lost at any point in time is small but as it is happening on a regular basis it amounts to a larger problem.

That's what is being said by "small"

^This^

 

[Hagen]

If too hot temperature of the oil in the gearbox causes the breather to leak oil, then there could be some longterm problems. Thats because lower operating temps mean longer lasting fluid and internal components increasing your transmissions life expectancy.

I don't no the specs of the Shell oil, but I expect this automatic gearbox diagram is about the same for Shell oil.

An expansion vessel or a tube to place the breather higher, isn't the solution in mine opinion, because that won't lower the temperature.

If I am right (I hope not), the only longterm solution is to replace the gearboxes with those better cooled.

 

[WigglePig]

If too hot temperature of the oil in the gearbox causes the breather to leak oil, then there could be some longterm problems. Thats because lower operating temps mean longer lasting fluid and internal components increasing your transmissions life expectancy.

I don't no the specs of the Shell oil, but I expect this automatic gearbox diagram is about the same for Shell oil.

View attachment 15364

That is for a traditional automatic gearbox and doesn't really apply here...the reduction drive is much more like a differential in operating conditions.

An expansion vessel or a tube to place the breather higher, isn't the solution in mine opinion, because that won't lower the temperature.

Well, preliminary indications from the rolling road tests at the weekend are most interesting...under the conditions invoked by the tests (70 mph continuous from 100% SoC to 20%) neither the 5 nor the 4 reduction drives suffered any outlandish heat issues, developed any significant pressure or exhibited any unexpected behaviour. Both 'boxes ran at around 90-95degC at peak and had been checked and topped up with the correct amount of the correct grade of oil.

The 4 'box ejected about 1.5 ml of oil over the test whereas the 5 ejected none (not a surprise) but there was a tiny touch of noticeable oil mist when fully heated.

As a comparison/control, the Citroen Ami was subjected to a similar test (100% to 20% at continuous full rated speed) and nothing untoward was noted, although it was much more relaxing and took a while...

If too hot temperature of the oil in the gearbox causes the breather to leak oil, then there could be some longterm problems. Thats because lower operating temps mean longer lasting fluid and internal components increasing your transmissions life expectancy.

I don't no the specs of the Shell oil, but I expect this automatic gearbox diagram is about the same for Shell oil.

View attachment 15364

The issue is NOT caused by excessive heating but by the positioning of the breather fitting directly in line of the crown wheel oil fling. As things heat up the expansion of air/oil in the 'box seems to push tiny blobs of oil out of the breather after they are thrown into the channel.

If I am right (I hope not), the only longterm solution is to replace the gearboxes with those better cooled.

I would suspect that the unit which was reported to have discoloured oil may be suffering from excess heating due to misalignment, damage or poor setup during assembly.

 

[Cocijo]

Well, preliminary indications from the rolling road tests at the weekend are most interesting...under the conditions invoked by the tests (70 mph continuous from 100% SoC to 20%) neither the 5 nor the 4 reduction drives suffered any outlandish heat issues, developed any significant pressure or exhibited any unexpected behaviour. Both 'boxes ran at around 90-95degC at peak and had been checked and topped up with the correct amount of the correct grade of oil.

The 4 'box ejected about 1.5 ml of oil over the test whereas the 5 ejected none (not a surprise) but there was a tiny touch of noticeable oil mist when fully heated.

As a comparison/control, the Citroen Ami was subjected to a similar test (100% to 20% at continuous full rated speed) and nothing untoward was noted, although it was much more relaxing and took a while...

That test must have taken hours on the rolling road.