c o l u m n

Jim Winsor • Executive Editor
On Equipment

Be Careful With Winter Fronts

Improper use shortens life of fans, fan clutches and charge air coolers.

With cold weather now on the scene in large parts of the country, winter fronts, sometimes referred to as radiator covers, are showing up on more and more rigs.
Many drivers seem to feel that when the temperature drops below freezing, the best way to keep the engine and cab warm is by blocking air flow through the radiator. What most drivers either don’t know or don’t care about is the costly damage and shortened life that improper blocking can cause.
From a technical view, winter fronts are not necessary except in extremely cold temperatures or with very light engine loads and with a high rate of engine idling. Today’s cooling systems, with vastly improved coolant circulation controls and thermostats, usually will keep coolant temperatures in the 160° to 180° range. Virtually all diesels, small or large, now have fan clutches or viscous fan drives as standard equipment. Fans are either disconnected or turning slowly when cooling isn’t required.
Today’s systems are a far cry from the “old days,” with fixed-drive fans that pulled the same air volumes through the radiator core, hot or cold. Old-timers like me remember automatic radiator shutters that were closed much of the time to keep cold air out of the engine compartment. Shutters are still available as special-order equipment for the rare situation of constant subzero operation.
Almost all diesels today have charge air coolers, which are air-to-air heat exchangers mounted on the front side of radiators to cool the hot pressurized turbocharged air before it enters the cylinders. It’s vitally important that a minimum amount of air, as specified by the engine manufacturer, pass through these coolers or turbo air will be too hot, in which case performance, fuel economy and emissions all suffer.
To protect your company’s trucks when winter fronts are being used, make sure they are the right size and shape so equal air flow is passing through from the top, bottom and each side. Here’s why this is important:
If air flow is blocked off unevenly, fan blades pass in and out of dead air and moving air so the load on the blades is constantly changing. This causes the blades to flex. The fan also needs sufficient ram air passing through the radiator core so the fan clutch isn’t engaging unnecessarily. Air must pass over the temperature sensors on viscous drive fans. If cool ram air is blocked from reaching the sensor, it sees hot air and engages the fan.
Another factor, now being studied by a new task force of The Maintenance Council, is the effect blocked air flow has on the life of the charge air cooler. There is a major change in the expansion rate of tubes in the cooler when they are blocked by winter fronts. The differential expansion rate, which is as high as 3-to-1 when ram air is blocked, causes joints in the cooler to fail prematurely.
Charge air cooler manufacturers report that upward of 100,000 coolers fail annually, and they think that air blockage from improper winter fronts is a major contributor to these failures.
Each engine manufacturer has a minimum air-flow requirement for the charge air cooler. All manufacturers of 10- to 14-liter truck diesels call for a minimum of 120 square inches; that’s equivalent to an 11-by-11 opening.
As a rule of thumb, drivers should be instructed to never close off an area less than 1 foot square, and that area should be centered in the middle of the radiator/charge air cooler. NEVER allow cardboard or other homemade covers to block air flow. If drivers complain about cold cabs, find the problem and correct it. Maybe it’s a stuck thermostat or air leakage through holes in the firewall or around the pedals.
Blocking off air flow through the radiator is not a solution.