..... The old Focus is still on its original exhaust (2007) although about fours years ago the metal support rusted through but the local garage I use for servicing welded it for a tenner.

Probably the same item my indy welded for the same price on our Focus at 16yrs old! No further problem till sc***ped at 21yrs old.

Many years ago, a vintage MG owning instructor at technical college explained how he rust proofed a replacement exhaust for it.

Plugged one end, filled it with (used I think) engine oil and left it for a couple of hours. Drained the oil, fitted the exhaust to the car and gave it a good blast on a quiet road (lots of smoke till the oil had fully dried on). No idea how effective it would be, but he was certainly convinced by it!.

Hmm...I suppose the areas it burns off off quickly are not the areas that will suffer worst from condensation -induced corrosion, and *providing it isn;t VERY used, the base in the engine oil will have an antacid effect., so it might work, though these days a vintage MG exhaust replacement would probably be stainless steel.

Still think my aluminium / cement treatment is likely to be better, though I suppose one could do both, I wonder how vegetable oil, which will set, (or a mixture) would compare.

I would be a bit concerned about the possible effect of the oil on the HC reading in the MOT emission test, though.

Of course I wouldn't risk either on a cat-equipped system, but I've never had one of them

Edited by edlithgow on 05/10/2023 at 08:53

Many years ago, a vintage MG owning instructor at technical college explained how he rust proofed a replacement exhaust for it.

Plugged one end, filled it with (used I think) engine oil and left it for a couple of hours. Drained the oil, fitted the exhaust to the car and gave it a good blast on a quiet road (lots of smoke till the oil had fully dried on). No idea how effective it would be, but he was certainly convinced by it!.

70s Japanese 4-stroke bikes used to rot their OE exhausts from the inside out because of acidic condensates in the exhaust gas.

So some fastidious owners preserved their OE systems by plugging one end, pouring in about half a pint of smooth Hammerite, plugging the other end and then shaking/tipping the pipes so the paint covered all the internal surfaces. The pipe would then be hung up overnight with one end open to drain the excess paint and dry off.

My mild steel non cat exhaust was still fully intact when The Man got it recently, though it had lost the original surface treatment on the front half. Car was 1986. I had it about 15 years, and I dont remember any exhaust replacements listed in the partial translation of the dealer service record I got when I bought the car..

Of course no salting and high ambient temperatures here in Taiwan are probably a factor

I did get the downpipe replaced (with a used one) because it got clouted by a brick and had cracked, GF's mechanic uncle did the job, and screwed up the flange bolts (I let a Taiwanese mechanic touch my car so got what I deserved) and I had to bodge it fairly regularly until I finally got around to fixing it semi-permanently, a non-trivial job.

tw.forumosa.com/t/exhausting-all-options/193821

The regular bodging meant I could regularly apply my internal protective treatment. some beer can aluminium in the downpipe, which I fondly imagined would flame-spray the inside, and a teaspoon of Portland Cement to neutralise acids.

Latterly I wrapped the front half in aluminium aircon pipe cladding, with another layer of overlapping beercan on the straight section. In combination with a bit of an oil leak this seemed to have stopped the surface rusting

Looked like it would probably have lasted for a long time

I think most if not all modern cars come with stainless steel exhausts.

Not my experience! Can you imagine the penny pinching manufacturers going to that extra expense?