Those engines aren't used in trains through. They are used in boats.

A large industrial diesel engine is about the size of a house and displacement is measured in cubic meters.

No. Large industrial oro marine diesel engines are not truck engines.

The engine isn't in the trailer. That is in the tractor, which pulls a trailer.

If OP meant "fueled by unrefined oil" then sure, but I didn't even consider that to be an option.

The heavier crude grades cannot be (realistically, at least) put into trailers or tanker cars - which is what I thought was being implied here for the Gulf oil sources.