Why cool your fuel?

[Lonesome7.3]

I noticed lately that some people are cooling their diesel fuel. I know in a gasser that is a good thing and helps performance. But I was under the impression it is better to heat your diesel fuel. Was I taught wrong? What are the benefits of installing a fuel cooler on your diesel powered vehicle?

[THEFERMANATOR]

It mainly depends on the engine. Diesel fuel is most efficient at about 150 degrees, and at 180 degrees or so it becomes thin and loses some of it's lubricating qualities as well as thins out in general and gets harder to compress. Common rail injection diesels use fuel coolers because of the high pressures and it also is used to keep the injectors cooled down some as well. And on the DURAMAX the fuel circulating cools the injector driver module that fires the injectors. It's mostly about checks and balances though, you want the fuel at a certain temp range for peak performance.

[Lonesome7.3]

Is there a way to install a cooler or heater that kicks on when needed? Like the way a thermastat works for your cooling system.