Corrosion to sills by rear wheel arches - is this common?

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My Name: PVR

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Hi Folks,

Well the good old C3 has just passed yet another MOT without any fuss and I have to say we really like our little car.

But.... there's the beginnings of corrosion to the bottom of the sills a few inches in from the rear just before the start of the rear wheel arch. If you push hard with your fingers you can feel the sill moving so the dreaded rot has started. Our MOT chap says that this often goes unnoticed because of the thick layer of sealant that is applied to the sills. It's OK for now but I want to sort the issue out a) before it spreads and b) before next year's MOT.

So here's the questions: Has anyone had this corrosion problem with the sills on their C3? If you have - what did you do - replace the entire sill or just the back section? Was it a good lasting repair?
Anyone got any other advice? Do you know of other areas on the C3 that are prone to corrosion that we should be looking out for, and if so, where are they?

We'd very much like to keep this car, it's great in all other respects :)

Cheers,
Steve.
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Hi PVR
PVR wrote:Well the good old C3 has just passed yet another MOT without any fuss and I have to say we really like our little car.
Great.
PVR wrote:So here's the questions: Has anyone had this corrosion problem with the sills on their C3?
I will be checking mine over the next few days and report back. As for the rest of the C3 on a 2002 the only part with rust was the rear exhaust hanger that has been spotted so far.
My Name: PVR

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Hi C3car and thanks for your reply, I'm looking forward to reading your findings and, of course, hope that all is well and good with your sills ;)

I'm judging by the lack of responses to my questions I'm guessing that this corrosion thing is not a common issue with the older cars like ours - we have a 2003 model. However, it would be helpful to hear from other owners of vehicles this age what as to the condition of their sills.

Meanwhile I am going to visit a couple of local bodyshops this week and see what they say, so, watch this space.

Cheers,
Steve.
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PVR wrote:Hi C3car and thanks for your reply, I'm looking forward to reading your findings and, of course, hope that all is well and good with your sills
I checked my (red) 2002 and the sills are fine. No flexing or movement under the underseal.

PVR wrote:I'm judging by the lack of responses to my questions I'm guessing that this corrosion thing is not a common issue with the older cars like ours - we have a 2003 model. However, it would be helpful to hear from other owners of vehicles this age what as to the condition of their sills.
Its not a very high traffic forum, but you may get some information from Bogwoppit32 who has a topic
citroen-c3-questions/ecu-swap-from-abs- ... 72-10.html

and has a collection of C3 ;)

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I have just also tested a 2003 (blue) and there is some movement in the rear sill !! :shock: :shock:

I can feel the metal move under the underseal and hear the crunching as I push the underseal on the sill near the rear wheel arch.
At 6 seconds you can hear a crunch as the rusty metal moves under the underseal. The car is a 2003 model in blue and has a brand new 12 month MOT.
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Many thanks for posting that video, it shows the exact same thing I am talking about. :( :(

Now, to work out what best to do about it :?


Cheers,

Steve.
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PVR wrote:Many thanks for posting that video, it shows the exact same thing I am talking about. :( :(
I think its going to be a common problem and only just discovered.
PVR wrote:Now, to work out what best to do about it :?
Yes, its going to need the underseal stripping off and an inspection for a start.

It would be great if you get any more information or pictures to keep this topic updated as the info comes in :)
My Name: PVR

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I have found (today) a friendly local place who are well able to do the welding with a view to making it cosmetically good again and halting the progress of further rot rather than just stitching a plate on there and covering it in black gunk to pass an MOT.
After we had a good look and a chat the initial plan is to strip the paint and sealant back to determine the extent of the problem and then to carefully weld in the repair. To rustproof the repair along with the welding and to best prevent any future re-occurrence of the problem, our idea is (after first removing the rear wheel arch liners to do the welding) to drill a hole in the lower front of the rear wheel arch to access the inside of the sill, and then insert a tube and spray the entire length of the sill liberally with a wax rustproofer like waxoyl or similar. Finally, the hole is sealed with a rubber blanking plug and the plastic wheel arch liners replaced. The plug can be removed every so often for 'topping up' if needed.

I'll certainly take some photos and keep this post updated as things progress but for now all is on hold for a while as I have some busy work weeks coming up.

Meanwhile what are folks opinions of the best liquid or waxy rustproofers to use? I'm sort of fancying something a bit softer than Waxoyl as I seem to remember that it dries out and cracks after a while. Someone once suggested to me that mixing a little old engine oil in with it stopped that from happening....

All ideas welcome :)

So more to follow in a few weeks to a month's time.

Cheers,
Steve.
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Year: 2002 (02)
Engine Size: 1.4 (16v)
Fuel Type: Diesel
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Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: No
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Hi Steve, thanks for the work you are putting in :)
PVR wrote:I have found (today) a friendly local place who are well able to do the welding with a view to making it cosmetically good again and halting the progress of further rot rather than just stitching a plate on there and covering it in black gunk to pass an MOT.
This is great news.
PVR wrote:After we had a good look and a chat the initial plan is to strip the paint and sealant back to determine the extent of the problem and then to carefully weld in the repair. To rustproof the repair along with the welding and to best prevent any future re-occurrence of the problem, our idea is (after first removing the rear wheel arch liners to do the welding) to drill a hole in the lower front of the rear wheel arch to access the inside of the sill, and then insert a tube and spray the entire length of the sill liberally with a wax rustproofer like waxoyl or similar. Finally, the hole is sealed with a rubber blanking plug and the plastic wheel arch liners replaced. The plug can be removed every so often for 'topping up' if needed.
This does sound like the 'right' way to do it. Maybe it will take more time but will do a much longer lasting job than tacking a plate over the soft bit and covering in black.
PVR wrote:I'll certainly take some photos and keep this post updated as things progress but for now all is on hold for a while as I have some busy work weeks coming up.
I am sure the rust can wait a while :lol:
PVR wrote:Meanwhile what are folks opinions of the best liquid or waxy rustproofers to use? I'm sort of fancying something a bit softer than Waxoyl as I seem to remember that it dries out and cracks after a while. Someone once suggested to me that mixing a little old engine oil in with it stopped that from happening....
Something a bit thinner than the underbody waxoyl would be good, something like the Dinitrol ML3125 Cavity Wax which is designed for coating inside box section and sills.
Dinitrol ML3125 Cavity Wax wrote:For use in box sections and pre-application of underbody wax. Capable of good penetration into crevices and joints, it penetrates through rust. Dries to leave a brown, waxy, water-repellent protective film giving excellent rust protection.
Its available in aerosol in this link to Amazon sellers Dinitrol 3125 Cavity Wax for application without a compressor which could be better for a preventative measure.
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I've used a cavity wax called M8 Protector, it's a similar idea to Dinitrol, it also comes in an aerosol with a long tube to go inside hollow sections. This product is clear which I found useful when it squirts out of drain holes or other openings in the section you're treating.

How the rust treating properties compare? I've know idea yet, ask me in 10 years :lol:

When we got out C3 I did notice that the paint/seal wasn't so good at the front bottom edge of the rear wheel arches. Along the lip of the metal that forms the arch and just behind (which is a dirt trap) was chipped/worn away. I wonder if this could be where the corrosion starts? I was able to touch up the paintwork and apply loads of underseal on the inside of the arch at the bottom, hopefully that's nipped any problem in the bud.
If at first you don't succeed, destroy all the evidence and pretend you never tried :lol:
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