Exhaust emissions control technology has substantially increased the heat rejection requirements of heavy-duty diesels. OEMs have responded by increasing the pressure of engine cooling systems. This has contributed to higher underhood temperatures, to the detriment of components located in this hostile environment -- a situation that has been addressed by some new design technology. According to experts from The International Heat Transfer Association, the mileage on a vehicle is not as big a factor in the maintenance requirements of a cooling system as is the vehicle's age. There is one area in which fleets have an opportunity to save a few dollars. Leaks from hoses and hose connections have been addressed in many cases by using relatively expensive silicone systems. Coolants are commonly placed into one of two general categories: conventional fully formulated or extended life products.