Gary G Posted December 30, 2002 Share Posted December 30, 2002 My 4-1 exhaust is highly polished and has been a coppery colour (outside the engine bay) since I bought the car in May. Just cleaned it today with Autosol (as I've done many times before) and it is now more of a silver colour. Is there any reason for this? C7 GAR Link to comment Share on other sites More sharing options...
Jason Plato Posted December 30, 2002 Share Posted December 30, 2002 Maybe this time you simply rubbed it a bit harder ?? Link to comment Share on other sites More sharing options...
sieds Posted December 30, 2002 Share Posted December 30, 2002 If you wrun it for a couple of hours the coppery color returns caused by the heat. Keep on polishing Link to comment Share on other sites More sharing options...
Rob Walker Posted December 31, 2002 Share Posted December 31, 2002 Gary, The brown film is just the Stainless Steel oxidizing due to the high temp of the exhaust gases passing through and heating the tube, a good thrashing on a track on a hot day will produce a deeper brown colour. This is the same effect as when you temper steel, as the steel is heated to about 350C a straw coloured oxide forms on cooling if you heat a bit more 450C the oxide turns blue. Therefore if you see your manifold turn blue outside the engine bay this is a good indicator that either you have a weak mixture or your timing is out. Rob Link to comment Share on other sites More sharing options...
Gary G Posted December 31, 2002 Author Share Posted December 31, 2002 Thanks for your replies. The heat thing makes sense, because I've driven the car very little over the last 2 months and the exhaust has therefore not been very hot. C7 GAR Link to comment Share on other sites More sharing options...
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