1. The IC may cause a slight increase in water temp, but not enought to hurt anything. IF it does, I would suspect the radiator is full of crud and marginal anyway.
2. The IC does drop boost pressure, but it also lowers the temp of the charge air, making it more dense, and carrying more oxygen. This make up for the lost boost, also, you can turn the fuel up more, since the EGT's will be lower and regain some of the lost boost, and and gain even more power than before the IC.
3. Am more efficent engine, even thought it has the ability to use more fuel, the mpg's shoud go up, because the engine is not working as hard to move the load. That is why guys that turn up the fuel, to a point, in any diesel see a slight increase in the mpg, because since the burn of the fuel is more complete in the cylinder, you don't have to add as much for the same output..........