Chronos wrote:Yep, the key with cast is to make sure it's clean including removing any rust and carbon then preheat over 150deg then just weld on a patch. Stainless steel has similar expansion/shrinkage rates to cast steel so it's common to use stainless electrodes on cast.
Chronos
THIS, welding non like metals is always finniky with heat, you really do need to make sure that whatever wire/rod you use is not going to expand or contract at vastly different rates than the parent metal. remembering that exhaust manifolds on diesels can get gasses in excess of 700 degrees when under heavy load. this makes a big difference, also heating up/cooling down, creek crossings, and driving into hail/rain and all that crud can have an effect too and over time, do as chronos says and will be your best bet, that or have a new manifold fabricated that doesn't have that hole/crack on it.