MG4 Reduction Gearbox Oil Leak

tsedge said:
I think it will remain a mystery until someone external with gearbox design expertise tears down the gearbox and gives us an independent explanation.
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I'm certainly no EV reduction box expert, but I think I can confidently say that the head scratching choice the designers of this box made with the positioning of the breather, is the core issue.

Around 4000 miles on, I still have zero leaks from a 900ml fill. I just used a sump plug adapter and brass elbow with a short tube on the fill hole, but with their resources, MG / SAIC could easily design something more elegant.
Really odd that they continue on this blinkered path with revision after revision. It's like a form of insanity IMO, doing the same thing over and over and expecting to get a different result o_O
 
Macadoodle said:
I'm certainly no EV reduction box expert, but I think I can confidently say that the head scratching choice the designers of this box made with the positioning of the breather, is the core issue.

Around 4000 miles on, I still have zero leaks from a 900ml fill. I just used a sump plug adapter and brass elbow with a short tube on the fill hole, but with their resources, MG / SAIC could easily design something more elegant.
Really odd that they continue on this blinkered path with revision after revision. It's like a form of insanity IMO, doing the same thing over and over and expecting to get a different result o_O
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In other words, common corporate behaviour!

I agree with you.
 
I still don't understand how the modified breather works for some people and not for others. In fact, where it's located (i.e. above the crown wheel) I can't see how it can not leak.

I can't comment on oil leaks prior to the mod, as my car was fitted with the first modification by the dealer before purchase. What I can say is that mine has not leaked - so far. But then, I don't have a bulge in the undertray either, so for all I know all the oil could have leaked out and is now sloshing around on top of the tray!
 
Sloucher said:
I still don't understand how the modified breather works for some people and not for others. In fact, where it's located (i.e. above the crown wheel) I can't see how it can not leak.

I can't comment on oil leaks prior to the mod, as my car was fitted with the first modification by the dealer before purchase. What I can say is that mine has not leaked - so far. But then, I don't have a bulge in the undertray either, so for all I know all the oil could have leaked out and is now sloshing around on top of the tray!
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It would have made itself seen , it will creep through the smallest gap and spread itself as well as dripping onto your drive. You are like me no apparent leak , probably less than 700 ml , but won't be checking just yet.
 
AndyL61 said:
It would have made itself seen , it will creep through the smallest gap and spread itself as well as dripping onto your drive. You are like me no apparent leak , probably less than 700 ml , but won't be checking just yet.
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Admittedly mine has only covered just under 1500 miles, but (touch wood) no drips on the drive yet.
 
Sloucher said:
Admittedly mine has only covered just under 1500 miles, but (touch wood) no drips on the drive yet.
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But like many others here with no leaks especially with recent purchases, we still do not know whether the oil level was reduced 200ml. or so to solve the issue as many have mentioned.

Perhaps I am overly suspicious but it just puzzles me that some do not leak and some do regardless of modified breathers and later models etc.

We all know that the reason they leak is due to the poor placement of the breather rather than the design so why do some leak and some do not?

They are all the same car manufactured in the same plant so they should all leak if they have the correct amount of fluid in the reduction 'box.. :unsure:
 
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wiz043 said:
We all know that the reason they leak is due to the poor placement of the breather rather than the design so why do some leak and some do not?
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Sorry but I think AndyL61 got it right. If it is a one way valve, as it seems to be, then it's very much the fault of bad design rather than placement.
AndyL61 said:
The idea is that there's no pressure build up at all , the only way to achieve that is to allow the cavity to breathe in both directions. That's why I couldn't understand why they would fit a one way ball valve in the original breather. They actually caused a build up then sudden release which will spit oil out as well as putting it in line with the main crown gear. So it became a double effect of allowing pressure to build and fitting the breather in the worst position. Just wrong, bad design.
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Rip Van said:
Sorry but I think AndyL61 got it right. If it is a one way valve, as it seems to be, then it's very much the fault of bad design rather than placement.
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I actually think the placement is also wrong. It is a combination of mainly bad placement, but also breather design. It's just completely wrong.
 
AndyL61 said:
I actually think the placement is also wrong. It is a combination of mainly bad placement, but also breather design. It's just completely wrong.
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The one way ball bearing valve did result in 'slugs' of oil being trapped in my mega tube routed up behind the back bumper, definitely didn't help the situation.
Removing the valve didn't cure the problem though, with 900ml the box still pumped oil all the way up to the end of the long tube and covered the outside of the bumper in an oily mess as it seeped through the gaps ... nice :giggle:

Contrast that with simply going for a side mounting, she's happy with just 5 inches and the tip remains dry at all times ;) Positioning is the key methinks.
 
Rip Van said:
Sorry but I think AndyL61 got it right. If it is a one way valve, as it seems to be, then it's very much the fault of bad design rather than placement.
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Definitely placement in my view. It is right in line with gears revolving quite fast especially as the car speed increases and regardless of breather design which would need some sort of outlet, oil is going to be pushed out there even if the oil is not fully covering the gears.
The obvious placement of a breather is more to the side of the 'box as @Macadoodle discovered with his mod.
 
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wiz043 said:
Definitely placement in my view. It is right in line with gears revolving quite fast especially as the car speed increases and regardless of breather design which would need some sort of outlet oil is going to be pushed out there even if the oil is not fully covering the gears.
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This might be one of the reasons why some cars don't seem to leak. Maybe they are only driven in an urban environment of not very frequently at all.
 
Rolfe said:
I live in a rural area and drive 50 miles into town quite often. I've also driven on the motorway to Yorkshire and back. Never seen a leak.
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Built January, 2023, well after oil leak complaints started.

It's great that it doesn't leak along with many other MG4's that were built in recent times and I do not mean to be negative but to my knowledge they still have the modified breather that was later fitted to older cars with the oil leak issue to no avail in many cases.

As mentioned before regardless of whether the vehicle is an earlier model with the latest breather or a recent model with the same breather if one leaks then they should all leak as they all came out of the same factory.
The jury is still out on whether speed is a factor although it makes sense that they should leak more at speed but it's a bit difficult to look under the car at 70mph. ;)

As many here have indicated it is possible that the correct oil level has been reduced from 900ml. in the newer cars to 'solve' the problem and we won't really know unless someone drains the oil down the track and 'spills the beans'. :unsure:
 
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Rolfe said:
I live in a rural area and drive 50 miles into town quite often. I've also driven on the motorway to Yorkshire and back. Never seen a leak.
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That's great and I hope it stays that way. :) Makes it more mysterious still.

Some time ago I have linked a video showing that really a lot of oil has to spill into the plastic floor cover before it actually leaks to the ground.
 
I thought the fact that my car was a 2023 build might mean it wasn't liable to the leak, but some people seem to think that it could happen nevertheless.

I've gone like a bat out of hell on the motorway more than once, but not seen anything. My old Golf leaked engine oil and all I have seen is the remains of that on the drive and the garage floor, nothing fresh.
 
Rolfe said:
I thought the fact that my car was a 2023 build might mean it wasn't liable to the leak, but some people seem to think that it could happen nevertheless.

I've gone like a bat out of hell on the motorway more than once, but not seen anything. My old Golf leaked engine oil and all I have seen is the remains of that on the drive and the garage floor, nothing fresh.
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Mine has not leaked , now over 5k miles with plenty of motorway driving. I don't even check it every week anymore. What we need to consider is that we don't know if any kind of internal baffle has been installed to stop the oil entering the breather pipe even though it is still in the same place. When this first occurred on the early cars , MG engineers must have come to the same conclusion that we did in that if you are going to position a breather in direct line of oil throw then chances are it will leak. The mark 2 or even mark 3 breathers were an attempt to cure the early boxes , but they will not have enough effect if the fundamental problem is still there. So I think that maybe later batches of gearbox have an internal baffle fitted to stop oil going into the breather in the first place. They have also fitted the modified breather for good measure. Another theory and to explain the early cars that haven't leaked could be that some boxes were manufactured with this baffling missed off (for reasons unknown) and consequently they would spew out oil in the fashion that we have seen. Any reduction in oil capacity was also an attempt to try to help reduce the leaks. Anyway time will tell , in the meantime, us lucky souls who have leak free gearbox's can relax and enjoy the car .👍
 

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