Happy new year to all. I was attempting humor, and agree it's better to feel around radiator, hoses, etc. Diesels aren't really oily, are they?
Barrie, good point that measuring current draw will be definitive. I'd suggest that using current transformers is safer, at least to your multimeter. If you pick the wrong meter scale or unit setting...
Here is an interesting tool for measuring voltage and current which does not require you to break the circuit.
We have one at work, and it is a good tool for approximations. It won't give laboratory-accuracy but it will quickly tell you if circuit is hot and drawing current.