Kings of Cool

| April 07, 2005

Deposits, or “scale,” that come from cooling system neglect work as an insulator, holding heat in the radiator tubes – exactly what you don’t want. Even a very thin layer will mean the coolant’s temperature will drop less as it flows through, reducing radiator capacity. Deposits also slow down flow and can easily reach the point where they fully clog the thin passages inside the tubes.

This will soon result in a high operating temperature and, eventually, engine shutdown by the ECM. Another consequence: “The pump pulls the coolant through. It’s not a problem till the radiator tubes really get stopped up,” Erikson says. “With flows in the range of seven gallons per minute, the restriction will mean the water pump will start to pull in air because the seals in the cooling system are designed to keep coolant in, not air out.”

There are two low-maintenance ways to keep your cooling system clean inside to prevent this kind of trouble. Easy maintenance of both systems depends critically on adding only the right coolant. The worst thing is to add coolant designed for a car, not heavy-duty trucks, which will quickly leave the system unprotected against corrosion and may even foul it with silicates, an additive designed for the aluminum parts used in car cooling systems.

Darrell Hicks, the national truck OEM manager of Penray’s Power Fleet Division, says it can be difficult to get the proper coolant on the road, even at some truckstops. Keeping leaks to a minimum greatly increases the chances of making sure you’ll be able to top up with the right stuff. When you don’t have much leakage you’ll likely be able to carry enough of the right stuff with you.

The first step here, says Hicks, is simply to refill the system properly. Most trucks today use an overflow tank that allows you to see the coolant level right through it. The tank contains the coolant but without a pressure cap, so as soon as the level rises too high, it is lost. Often, drivers will fill the tank to the top. “Then,” says Hicks, “In only 25 miles, the coolant in the system expands and the fresh coolant is pushed out.” They keep filling the tank with any coolant they can get their hands on and soon the system has a significant amount of the wrong coolant in it.

“Fill the tank only to the level line,” Hicks say. “If you’ve overfilled it, and it’s pushed some coolant out, don’t refill it.”

If the truck uses a conventional radiator with only a top tank, fill it only to the correct level as specified in the owner’s manual – usually a couple inches below the cap opening even when warm.

Whenever you’re adding coolant repeatedly, “Find the leak,” Hicks says. “Why are you losing the fluid?”

The first thing to check is the radiator cap. You could be pushing fluid out through the cap, Erickson says. “The rubber seal can be so deteriorated a 7-pound cap will no longer be a 7-pound cap at all,” he says.

Remove the cap and inspect the seal. If it’s obviously cracked or grooved, replace the cap. Even if not, install a pressure tester, pump it up to the rating of the cap, and then watch to make sure the pressure is retained for two full minutes. If not, replace the cap. Erickson suggests replacing it every year or 120,000 miles. Check the rating carefully when replacing.
A good radiator cap will not only cure a common type of coolant leak, it will help keep coolant from boiling along the cylinder liner outside walls, helping to minimize cavitation erosion – a destructive acne-like pitting away of the cylinder liner. Erickson adds that keeping leakage to a minimum so the radiator stays full will also help minimize hot spots in the engine that can cause head gasket failure or even cracked cylinder heads.

Radiator repairs

“It shouldn’t be necessary to check for loose bolts in a modern cooling system,” Gary Falendysz of Modine says. “Most often, these fasteners have a self-locking feature that keeps them tight throughout the life of the product.” Erickson agrees such mounts have been made about as maintenance-free as they can be with a life of 300,000 to 400,000 miles.

But the high temperatures under the hood (often exceeding 275 degrees Fahrenheit) age rubber components over time. “Hoses, belts and rubber isolators can become dry and crack due to this heat,” Falendysz says. “Ozone also attacks these rubber components. Belts, hoses and rubber isolators should be replaced if they become hard or cracked.”

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