Originally Posted by Irishbleueye
So Kamafly, this post was very interesting to me. This last weekend we took a trip to L.A. County fair. It's only two and a half hours away. However we got stuck in traffic for 2 hrs and it was 100 degree day. The exhaust super heated and I assume the 02 sensor to the point where it shut down the fuel injection. We had to pull over and let it cool. All was fine after 30 minutes. After reading your post I realized these MH's can't get the heat out while sitting and I think this is the reason for all the cracked exhaust manifolds. Our MH only has 17,000 mi on it and so far the exhaust is ok. However I will now buy exhaust heat wrap and do the entire exhaust pipe to keep this from happening. Or hope anyway.. Thanks for posting..
I'd think wrapping the exhaust will do little to stop it from cracking. The stock manifold is a large cast iron piece of metal that is fastened by studs and bolts the length of the head. Expansion and contraction cause the cracks, especially if a bolt is rusted or too tight and stops the normal expansion/contraction movement from happening.
A header is a whole different animal, it's pipes allow for the expansion/contraction by being fastened separately at each exhaust port.
Wrapping the exhaust will only hold the heat in until further down the pipe, it will not stop the manifold from cracking. Proper slow warm up and a chance to cool after highway miles are far better to preserve the manifolds. To prevent the issue you had with an overheated O2 sensor you should have increased the idle speed occasionally to have the fan blow the heat away from the radiator and exhaust, not trap it in a 'blanket.'