Towing capacity vs. cooling capacity

Motor, Aug 1998 by Weissler, Paul

Towing capacity is important for two reasons: First, if you're buying a new truck or SUV for the shop, you may have to pull a load, even if towing in customers' cars is not the purpose. Second, if a customer's truck or SUV overheats, there's a chance the towing capacity is being exceeded.

You'd think it would be simple to determine towing capacity, but as we found out in preparing the '98 truck report last February, it isn't. The information on new vehicles may change many times, and even carryover vehicles may get a change in these ratings from year to year.

The case of three Chrysler vehicles-the Jeep Grand Cherokee, Dodge Dakota and Dodge Durango, a new SUV based on the Dakota-is a good example.

From the time of the initial Durango announcement until the final version (with the 5.9-liter V8) rolled out this spring, the towing capacity figures on the Durango were changing even faster than Chrysler's own people could keep track of.

When consumers look at a truck, they tend to look at peak towing capacity. They believe that the biggest engine can tow the most trailer weight. Not true.

The Jeep Grand Cherokee 5.9 Limited (with the big 360 V8) is being promoted as a 0-to-60 performance truck. Its towing capacity is just 5000 pounds, with a 3.73:1 the only rear axle ratio available. The limitation is imposed by the cooling system, which has an electric fan to reduce the power draw for acceleration. The smaller 5.2 V8 has a clutch fan, and its towing capacity is 6500 pounds. But there's a retrofit clutch fan kit available for the 5.9 V8 if the 6500-pound towing capacity is necessary.

The Dakota and Durango are both haulers. In fact, the Durango is being promoted as a high-tow-capacity SUV. So both get clutch fans for maximum cooling. In some trucks, including these, the towing capacity with 4WD is lower because of the limits of the transfer case or the transmission (in this case, some manuals have more, others less than the automatic) and the extra vehicle weight. And if we're talking truck cabs, a club or crew cab that holds extra passengers is obviously heavier than a regular cab, and that can make a difference of a few hundred pounds in towing capacity.

Another key factor that affects towing is rear axle ratio. As you'll see, it makes one of the biggest differences in the Durango. Here are some automatic transmission examples:

Although the Durango is based on the Dakota chassis, the Dakota has much higher towing capacities throughout the range of axle ratios. Here are some examples with the 5.2 VS and automatic transmission:

Bottom line is that lots of buyers of trucks and SUVs (often for the first time) may think they've bought the peak towing capacity, when they haven't. So their introduction to the truth may be when the vehicle overheats and comes into your shop on a hook. You've got to consider everything, particularly if you're trying to diagnose an overheat. This includes trying to determine if the truck is pulling too much weight. If the owner of a Dakota club cab thinks he can pull 6700 pounds with three large friends in the cab but the wrong driveline configuration, an overheat should not be a surprise.-PW