Good points guys.
I know many assume that German tanks ran on diesel. It is a very common myth. The main disadvantage of a diesel engine is the high weight involved with it vs the German Maybach engines, that used roller bearings on the mains, and a very light engine.
I forgot all about the S-boots to be honest with you! Heat can be an issue for sure. I know that the IXD1 used the engines from an S-boot to make a high speed sub on the surface, but the heat and white smoke they emitted was really bad for them. I found this segment most interesting from the study of German type IX's after the war-
http://www.uboatarchive.net/DesignSt...eIXC-S41-5.htm