OE exhaust corrosion

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plip1953
Posts: 400
Joined: Mon Aug 13, 2018 4:15 pm
Location: Leeds

OE exhaust corrosion

Post by plip1953 »

Probably around 10 years ago I decided to treat my '88 635CSi Highline to a new OE exhaust. But in fact I only needed the middle rear section as the front part, although the original, still looked ok.

But within a year or so the bottom front most part of the new rear box was showing signs of corrosion on the casing. And yet the car had hardly been used and was dry stored whenever off the road. All I could think was that the occasional starting of the engine during laid up periods must be leaving acidic water residue in this part of the silencer, and that in future I should either run the engine longer to get everything properly warmed up or not bother at all. The corrosion continued, and worsened, but strangely there was no sign of exhaust gas getting out (it passed it's MOTs no problem).

Moving on quite a few years i decided the only thing to do was buy another OE system before they become N/A. So I did this, both parts, and stored it away for eventual use.

A few weeks ago I got the car out of long-term hibernation and took it along for its MOT. And again it passed no problem, bit I could see that by now the exhaust corrosion was really extensive, and yet still not blowing!

Nevertheless I thought it was probably time to bite the bullet and put the new unit on the car. So off came the old system - what a heavy lump! - and ready for the new one to slot in. But then I started taking a closer look at the areas of corrosion and made a surprising discovery. In the first pic you can see that a large part of the outer casing of the back box has corroded away. And immediately below the skin is lot of crumbly rust. But having scraped away the worst of it there seems below that to be shiny metal which I assume must be stainless steel?
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The centre box has a similar, particularly bad, section of corrosion on its underside, but here again there appears to be a layer of shiny metal below.
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By contrast the front section of the exhaust, now 30 years on the car, appears totally serviceable and with no real corrosion of the front silencer box whatsoever!! So I might even give it a lick of paint and use it a while longer :-)
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Phil
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1988 Highline 635 CSi
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