Since this winter doesn't want to go away (Spring officially started yesterday, but it's still snowing, 25cm expected tonight, and it'll be below freezing for at least another week), I have lots of time to think about engine insulation, cold starts, etc.
I really liked how Brucepick
insulated his valve cover with (what I think is) a rubber foam. After reading through his thread I had a long look at my engine and had to frown: The valve cover has plastic on it, plus everything (injectors, glow plugs, cables) is so close together that it would be hard to squeeze any insulation in between. So I looked at the engine block itself, but I can't see it - there are so many things hanging on it, too close to put insulation under them. The only place that has some free surface area is the oil pan, which looks like this:
Over the summer I'll try to insulate the sides to keep more heat from the heating pad in. Also it should keep the oil warmer after killing the engine. I've found rubber foam in all sorts of thicknesses, from 3mm to 25mm, I'll probably settle for ~7mm. I'd like to cover the bottom as well, but the heating pad's instructions warned against that, though I wonder if a thin layer (3-5mm) would do any harm.
Maybe I could insulate the cat converter's housing also, to keep it warm? It is in front of the engine, so it gets hit with cold air coming in through the grille (when open).
Another thought: Since I normally have the intercooler unblocked, the air that goes through it cools the engine bay down. I guess that some fresh, cool air is good in the summer, but what about deflecting that air away from the engine itself - right now it hits the alternator, A/C compressor, and the timing belt cover. This is the end of the engine that needs insulation, I can see this is where most of the heat escapes when preheating.