There are heavy duty fan clutches and light duty fan clutches. The light duty ones are used on the pick-ups and light duty trucks with the 8.1 engine. The same goes for water pumps. There are many pumps that will fit the 8.1L engine but the correct one is extra heavy duty and has a much larger bearing to support the weight of the very heavy fan clutch. Use a light duty water pump with the heavy fan clutch and it will soon fail. Use a light duty fan clutch on your RV and it will not cool properly and will probably lock up much sooner so you can enjoy the engine roar sooner during your trips. The Workhorse fan clutches were made by Hayden and I would try to find a Hayden distributor that can find the exact replacement. Use a pick-up fan clutch and you will save money and be sorry for the noise that you will have to endure.
