I took Mrs D's Panda (Nov 2012 registered) for a spin yesterday evening and drove through some (not deep) water. Shortly afterwards I heard a scraping noise and discovered the rusted rear box cover had become half-detatched.
On closer inspection this morning, the actual rear box looks fine (no perforations) and only mildly corroded, but the outer protective cover is clearly defunct.

The last MOT had this 'advisory': "exhaust tail pipe outer skin corroding"

I'll try to get it off (it is still being held in place somewhere), but three questions now:
1. Is the cover an integral part of the rear box ? If not ...
2. Is the protective cover an available part and if so, where is the best place to look ?
3. As we don't actually take the Panda off-road (we have it for steep hills in the snow), is it essential to replace either the cover or the box itself (which currently has no perforations) ?

Think you'll find that the rusted bit is just the outer casing of a twin walled rear box. I removed my rear box completely, and fitted a plastic one with stainless internals. It will outlast the car.

You can also just remove the box and substitute a length of tailpipe, with very little extra noise and no future worries.

NigelDay said:

I took Mrs D's Panda (Nov 2012 registered) for a spin yesterday evening and drove through some (not deep) water. Shortly afterwards I heard a scraping noise and discovered the rusted rear box cover had become half-detatched.
On closer inspection this morning, the actual rear box looks fine (no perforations) and only mildly corroded, but the outer protective cover is clearly defunct.

The last MOT had this 'advisory': "exhaust tail pipe outer skin corroding"

I'll try to get it off (it is still being held in place somewhere), but three questions now:
1. Is the cover an integral part of the rear box ? If not ...
2. Is the protective cover an available part and if so, where is the best place to look ?
3. As we don't actually take the Panda off-road (we have it for steep hills in the snow), is it essential to replace either the cover or the box itself (which currently has no perforations) ?

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1. Yes, but they frequently detach due to corrosion. Once partially detached, they often rattle; if it does, just remove the outer skin.
2. No.
3. No. You can remove the outer skin by any means at your disposal. Provided the box isn't leaking through the inner skin, it will still pass an MOT just fine. They sometimes go on for several years in this condition before failing outright.

I cut one off with a nibbler.

Lasted several years.


I have also used a jigsaw and a metal blade.

Thanks folks. This afternoon I did actually remove the rusted cover. It was only being held on by about 1cm of metal, so I was able to cut through this quite easily. The inner cover is in good condition, with only minimal rust. I wonder if the sleeved design is actually the 'problem'. If it develops any perforation, water can ingress and then remain in situ causing rusting from the inside.
Anyway, I took the car for a long 2 hour drive this evening, over the hills and down the M6. It ran perfectly, and the occasional rattle I had noticed has now disappeared.

NigelDay said:

I wonder if the sleeved design is actually the 'problem'. If it develops any perforation, water can ingress and then remain in situ causing rusting from the inside.

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It's commonly believed that exhausts rust from the inside out (and they do), but the reality is that they rust from both sides. Usually, but not always, the failure point is along a seam, since the protective coatings on the steel stock are burnt off by the welding process when the exhaust is made in the factory (plus the seams are a natural trap for water).

If you do something to give additional protection to the seams when the exhaust is new, it may last a bit longer (though internal corrosion will always get a mild steel exhaust in the end). This may sound bizarre, but rubbing copper grease into the seams is quite effective - just make sure the car is parked outside when you first run it, as the smoke from the initial burn off of the solvents can be spectacular! The residue will fill the seams and forms a useful additional barrier against corrosion.

I did this to the exhaust on my Mk1 Ka when I first took delivery; it was still sound when I sold the car 10yrs and 100,000 miles later.

... and diesel exhaust systems last longer than petrol systems.

Sweetsixteen said:

... and diesel exhaust systems last longer than petrol systems.

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Yeah the Yellow Peril is still on original 12 years and 132K miles on.

Wee Smurf said:

Yeah the Yellow Peril is still on original 12 years and 132K miles on.

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Just another way that diesels are so kind to the environment!