MG4 Reduction Gearbox Oil Leak

[WigglePig]

The big red flag for me was the colour of macadoodles oil after just a few weeks

It's quite common for gearboxes and diffs to produce a little debris during run-in but the oil shouldn't really change colour. Darkening suggests the oil has got too hot which might suggest a poor alignment or preload problem in that particular example. I shall be draining and refilling my 5 soonsih so will see what the oil that comes out looks like.

 

[tsedge]

I’m thinking that this is the first rear wheel drive set up by MG. There has been no oil issues with their front wheel drive cars as far as I can see. Perhaps the transfer box runs cooler on FWD set up? Or perhaps just the designing the RWD transfer box has built in design flaws?

It isn't MG that makes it - contracted out to a 3rd party, hence the early confusion on the right oil level. I don't know who they are but presumably they specialise in transmissions and have done a variety of setups.

 

[Hagen]

It isn't MG that makes it - contracted out to a 3rd party, hence the early confusion on the right oil level. I don't know who they are but presumably they specialise in transmissions and have done a variety of setups.

The gearboxes in Tesla and VW Id.4 are liquid cooled. The Zoe (forwheel drive) has a fan to coole the gearbox I believe. It seems to me that de oil in the gearbox of the MG4 becomes to hot and therefore the pressure too high. I don't think that an expansion container or an longer pipe to the breather solves the problem. The oil in the gearbox must be cooled in one way or the other.
Bad thinking: maybe MG knows this issue and therefore makes an whole in the undertray to let air in for cooling purpose?

 

[tsedge]

The gearboxes in Tesla and VW Id.4 are liquid cooled. The Zoe (forwheel drive) has a fan to coole the gearbox I believe. It seems to me that de oil in the gearbox of the MG4 becomes to hot and therefore the pressure too high. I don't think that an expansion container or an longer pipe to the breather solves the problem. The oil in the gearbox must be cooled in one way or the other.
Bad thinking: maybe MG knows this issue and therefore makes an whole in the undertray to let air in for cooling purpose?

It would make sense that heat is the key factor since oil leaks seem to be reported after long runs and people have discoloured oil.

Pretty hard to retrofit a solution if that's the case unless there's provision already and space for an oil cooler.

But I am a bit baffled, rear drive transmissions are hardly new and the MG4 power and torque isn't huge, so why would this be any different? Is it something to do with regen?

 

[Cocijo]

The gearboxes in Tesla and VW Id.4 are liquid cooled. The Zoe (forwheel drive) has a fan to coole the gearbox I believe. It seems to me that de oil in the gearbox of the MG4 becomes to hot and therefore the pressure too high. I don't think that an expansion container or an longer pipe to the breather solves the problem. The oil in the gearbox must be cooled in one way or the other.
Bad thinking: maybe MG knows this issue and therefore makes an whole in the undertray to let air in for cooling purpose?

Conventional ICE transfer and transaxle gearing is not liquid cooled so I don’t see why an EV needs it. The motors - yes. Where do you get your information on Tesla and VW liquid cooled transfer boxes?

 

[Hagen]

Conventional ICE transfer and transaxle gearing is not liquid cooled so I don’t see why an EV needs it. The motors - yes. Where do you get your information on Tesla and VW liquid cooled transfer boxes?

Sandy Munro Examines Volkswagen ID.4's Electric Motor

Here is a very interesting and technical teardown of the Volkswagen ID.4's electric motor bu Munro Live.

insideevs.com

When you google on Tesla gearbox cooling, you find that these are liquid cooled

 

[Ian Key]

Just to put another thought into the discussion, I suppose MG have specified the correct grade of oil?

 

[WigglePig]

Stand by…I have borrowed a 4 to run some tests with on a rolling road.

But don’t tell anyone as it is a secret. ?

 

[WigglePig]

Just to put another thought into the discussion, I suppose MG have specified the correct grade of oil?

How many have reported discoloured oil due to overheating!

The grade and quantity of oil will have been specified by the gearbox manufacturer.

 

[Hagen]

Sandy Munro Examines Volkswagen ID.4's Electric Motor

Here is a very interesting and technical teardown of the Volkswagen ID.4's electric motor bu Munro Live.

insideevs.com

When you google on Tesla gearbox cooling, you find that these are liquid cooled

I saw a video of the Tesla model S motor and gearbox.
Liquid cooled just like the newer Tesla's.

 

[Macadoodle]

It's quite common for gearboxes and diffs to produce a little debris during run-in. I shall be draining and refilling my 5 soonsih so will see what the oil that comes out looks like.

Yes, the final 'polishing' of the gear teeth is really done in actual use and produces a very fine metallic silt. It will stop eventually but I'm less than convinced it's a good idea to leave these particles suspended in the oil for the car's life.
I must remember to point an infra red thermometer at the gearbox casing after a long run, just to see how hot it gets.
It is totally reliant on the oil for cooling as well as lubrication, a lot of work for a few hundred mil of oil to cope with, my old leaf has 1.4 litres if I recall correctly.
The highest temp I've measured in the 4's motor/ inverter coolant reservoir so far is 42 degrees , that doesn't really help the gearbox though.

 

[Deleted member 9909]

OK, some are external liquid cooled but back to the point...the MG4 which is not liquid cooled other than the interior oil...interesting to see what the rolling road test turns up...and your thermometer

 

[WigglePig]

Yes, the final 'polishing' of the gear teeth is really done in actual use and produces a very fine metallic silt. It will stop eventually but I'm less than convinced it's a good idea to leave these particles suspended in the oil for the car's life.
I must remember to point an infra red thermometer at the gearbox casing after a long run, just to see how hot it gets.
It is totally reliant on the oil for cooling as well as lubrication, a lot of work for a few hundred mil of oil to cope with, my old leaf has 1.4 litres if I recall correctly.
The highest temp I've measured in the 4's motor/ inverter coolant reservoir so far is 42 degrees , that doesn't really help the gearbox though.

Oh, absolutely. I shall be making measurements next week for temperatures, etc for a 4 and comparing it to my 5 over the same speed/distance.

Regarding the gearbox oil, much like any other I would prefer to change it after a few 000 miles just so that break-in debris is removed but I have had cars with gearbox oil that has not been changed until past 100kmiles and it has been fine.

More to come.

 

[dave99]

so I've done 1000 miles and just noticed what could be a bit of oil on the path so investigated underneath - I assume this is proof I have the oil issue (as well as the buckled undertray)

 

[Deleted member 10041]

As far as bulges go that's quite a small one. But definitely a leak

 

[Hagen]

OK, some are external liquid cooled but back to the point...the MG4 which is not liquid cooled other than the interior oil...interesting to see what the rolling road test turns up...and your thermometer

The MG4 is liquid cooled (see page 321 in the owners manual), however it works somehow not good enough for the gearbox?

When 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.

 

[Deleted member 9909]

I stand corrected...interesting to see what pumps coolant around the reduction gearbox in that case....

 

[Cocijo]

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 block.

 

[Ayoull]

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 block.

Every car I've owned has had an oil cooler built into the gearbox with coolant lines to the radiator

 

[Cocijo]

Really? I must have missed that then! I‘ve seen them on auto transmission but not manual.