Raggles said:
The exhaust is blowing a bit and I think needs replacing, which would provide the oxygen perhaps? I was not aware of the problem before the exhaust noise increased. Any tips on how to ensure that there are no leaks when fitting a new exhaust ... it would be the standard set up from VW heritage.
Few things... Get a small mirror and some fine GOOD QUALITY(the cheap stuff will just fill the area with bits of sand) sand the mating faces on the exhaust flat, and if you're careful, the outlets on the cylinder head too.
Make sure that the studs are wound in properly- they should be all the same length coming from the heads, and they shouldn't wobble.
I don't use any exhaust paste, these things were designed not to need it.
Replace the nuts with brass ones so you can remove them next time- they should have more than enough strength in them to torque up properly.
Don't be afraid to fit, bash, fit, bash, refit. They never go on properly the first time.
Don't do them up tight until every nut/bolt is in, as otherwise you'll find one part (usually the inlet manifold heat riser) just won't go on. It's terrible engineering practise working like that but hey, I don't make exhausts.
The main problem you're going to face is the quality of new exhausts- I put a new one on my bus less than six months ago, and wouldn't be surprised if the tailpipe showed a couple of pinholes in the next few months. Paint just burns off, so if you can go stainless I'd say it's worthwhile.
Oh=- and the burble is because of the exhaust. Especially since you mentioned it happening in enclosed spaces, tunnels etc. I have no idea why a holed exhaust sounds different when you're in places like that, but it does.
