Cooling Fans/Fan Drives

For this edition, we will be covering cooling systems and how to adapt a Cummins B series engine to an existing radiator. Often when engineering a cooling package, the complete package is engineered as a system. That is, the interaction between the fan, shroud, and radiator is optimized to minimize power consumption and noise and provide proper cooling under adverse conditions. To demonstrate this point, we can simply look at the fans used on the Cummins powered White American and 100 series tractors. Each model of tractor used a different fan that was optimized for each engine's specific heat rejection rate and the radiator that it was matched to.

To develop a cooling package, an equipment manufacturer will first obtain the heat rejection values from the engine manufacturer. Then a radiator will be selected that will fit the given envelope and have the fin and tube configuration needed to properly dissipate the heat generated by the engine. Finally, a fan will be selected where the restriction of the radiator is matched to the fan performance curve. This is a very simplified example of the engineering required to design a cooling package. It is not uncommon for several iterations to be required to achieve optimal system performance.

Without the analytical tools used by OEM's, it can be difficult to achieve the same level of optimization when performing a conversion; therefore some level of performance may be compromised. The components recommended in this article are general recommendations, but do not guarantee success. If problems are encountered, it is recommended to contact your local Cummins distributor and discuss your project with an application engineer who has experience designing cooling packages.

One option that can help overcome some of the unknowns when performing a conversion is to use a viscous fan drive which will modulate fan speed based on air temperature. One word of caution with viscous fan drives is that attention needs to be paid to hydraulic oil temperature when hydraulic intensive operations are being performed at times when engine loads are low. What can occur is that the heat rejection from the hydraulic circuit may not provide enough of an air temperature rise to trigger adequate fan lock up. Without enough fan speed, air flow may not be sufficient to extract enough heat from the hydraulic cooling circuit and overheating will result. In general, even a loosely coupled viscous drive will still move enough air to provide proper cooling, but it's important to watch out for such a condition.

Below are a number of general recommendations to assist with proper fan installation:

• Fan Depth Relative to Shroud:

  • The fan should be placed such that 60% of the width of the fan is forward (inside) of the shroud.

• Minimum Distance from Radiator to Front of Fan

  • It is recommended that the fan be a minimum of one fan thickness away from the face of the radiator.

• Maximum Gap Between Fan and Shroud

  • The radial gap between the fan and fan shroud should be no more than 1/3” to 1/2”.

• Fan Tip Speed

  • To minimize noise, fan tips speed should be less than 15,000 ft/min.

• Fan Power Consumption

  • Roughly 5-10% of gross engine power will typically go towards driving the fan.