OK, OK, ALMOST nothing. In a practical sense they do nothing. Trust me, I understand the theory behind them and how they are supposed to work, but honestly don't think they make much difference. Colder fuel means longer runtimes. In theory the coolers keep the fuel colder. But in practice the fuel tank sits right next to the exhaust anyway which puts a lot of heat into the fuel. It also picks up heat right off of the chassis(engine warms the chassis). Unless you insulate the tank and I mean more than just some aluminum heat tape, I really can't see there being a big heat reduction. Not by simply passing the exhaust gas through a 2 inch piece of finned aluminum. I understand the theory but I don't think what we have right now makes a big difference in practice. Maybe some day we will have more effective techniques to keep heat out of our fuel, but with what we have right now, I don't see it.