Traditionally brass nuts were always the material of choice on exhaust fittings and it worked well although you had to be just a little careful about how tight you did them or you could strip the threads. For that reason they were often "longer" than standard nuts thus giving a greater number of threads in engagement. They were also not known for slackening off and I think this was because there was a small amount of thread deformation which took place anyway due to the relative softness of the material. Interestingly, a couple of years ago I removed the cat on my '99 Cordoba TDI so I could weld a reinforcement where the pipe was blowing slightly. I had worried that the 4 nuts holding it to the turbo output flange would be rusted sold after being untouched for some 15 plus years. (I've owned this car since it was a year old so I know that pipe was as fitted at the factory) But, although access to one was difficult, they all undid fairly easily! I think this was due in part to the exhaust being protected running down the back of the engine as it does in this application but also, as I found when I bought new nuts, the nuts themselves were coated with what looked like copper (electro plated). The nuts themselves were also of the self locking type where the top couple of threads are deliberately deformed so they lock onto the male thread as you tighten them. That was actually partially why I decided to renew them as self locking nuts really only work, most effectively, once. Nyloc nuts don't work on exhausts of course because the heat melts the nylon so you might as well use ordinary nuts! Spring washers? Hmm? If they get hot enough they loose their "springyness" so you might as well use ordinary flat washers.
I became aware of ceramic based greases, for use on brakes, a number of years ago (I use Ceratec now a days, but that's mostly because my local factor stocks it). Then, about 4 years ago, there was a special offer of "Silver Hook, very high temperature ceramic grease and brake pad protector" - that's actually what is on the tub! - " operating temperature -20°C to +1500°C, protects metal parts against seizure, heat, corrosion, acid, water and also helps prevent disc brake squeel". Again, that's what is says on the tub! I just had to have some! When I started to use it I found it really quite runny, nothing like as "sticky" as the Ceratec or the more traditional Copaslip. So I stopped using it on brakes but I'm now using it in it's anti seize mode. For about the last 3 years I've been slapping it on exhaust fittings in particular. I used it on the cheap rear box I fitted to my daughter in law's Honda Jazz which, due to its cheap quality has just self destructed by fatigue fracturing it's pipe. (Inspection reveals further cracking and corrosion so a new, better quality this time, component was fitted). The interesting thing was that the ceramic Silver Hook grease which I had applied was still very much there. None of the fixings were seized but not loose either! The greasy component had obviously burnt away leaving a creamy white coloured deposit which was coating the threads and no corrosion could be seen on the mating threads although some was to be seen on the end of the threads where exposure had washed it away. Although not really enough time had passed to give it a really severe test, I am very impressed and will continue to use it for this purpose.
Hope these "ramblings" are helpful?
Regards
J.
