Royal flush

The most important single part of maintaining the liquid portion of the cooling system is using the same type of coolant, with the same protection technology, at all times.

Your truck’s cooling system is in a bigger squeeze than ever before. Creating a narrow, sloped hood with a small front opening is a critical part of building an aerodynamic cab that will save fuel at highway speeds. At the same time, truck engines now throw off more heat than ever before. A system that used to be able to provide reserve cooling capacity for summer’s heat now needs to be in perfect condition.

Air first
Your first step in preparing your cooling system for summer should be to check on the cleanliness and mechanical condition of your radiator and charge air cooler.

The “radiator” doesn’t radiate much heat. It actually transfers heat from a liquid to outside air. It crams the maximum amount of metal surface into the smallest amount of space, then heats as much air as possible with that metal. What results is a heat exchanger that has small, easily clogged passages, both inside and out.

Many years after the radiator was born, efforts at Volvo and Mack produced the chassis-mounted charge air cooler. When a turbocharger pressurizes the air, it heats it well beyond 350-400 degrees Fahrenheit. Engineers soon figured out that filling the engine with much cooler, denser air would not only make it more powerful, clean and efficient, but make it a lot easier to cool. Mike Powers, product development manager at Caterpillar, says that for every degree of the intake air temperature increase, exhaust temperature rises 3 degrees. So a problem with the charge air cooler could cause your engine to overheat even if the cooling system itself is working at 100 percent efficiency.

The charge air cooler also has confined passages that can easily trap dust and debris.
Some forms of debris – especially large bugs – not only fill the small passages and clog them, but stick there and form a heavy goo.

“Just how much effect bugs will have depends upon where you run and the time of year,” says Ed Saxman, powertrain marketing manager for Volvo Trucks of North America. “Love bugs are the worst. If you can hear them hitting the windshield, you know it’s important to be checking the cleanliness of the charge air cooler a short time later.”

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The problem with bugs, or any debris, is that they block airflow and form a barrier that blocks heat flow from the metal to the air. The result is a large downgrade of your cooling system’s efficiency.

Cleaning your radiator and charge air cooler is a job that should be performed regularly. The Detroit Diesel manual recommends checking hoses, piping and connections every 15,000 miles, and the core every 30,000.

Once the truck has accumulated a couple hundred thousand miles, the charge air cooler should be removed and cleaned from behind, and the best time to do the job would be right before summer. First, loosen the clamps and disconnect the hoses that connect the cooler to the turbo discharge pipe and the intake manifold. Then remove the bolts that connect the unit to its mounts.

Clean the cooler gently. Some manufacturers even recommend that the cooler be cleaned only by professionals. Use a radiator fin comb to loosen dirt stuck on the fins. Controlled air or water pressure (30 psi at most) can be used from the rear of the cooler. Especially at high miles or if the unit shows obvious cracks, have it pressure-tested at a dealer. This is done by teeing in a gauge, building up pressure to about 50 psi, and then watching to see how long it takes for the pressure to drop, says Chuck Blake, Detroit Diesel’s manager of customer fuel consumption analysis. If the cooler does not meet the required spec, it should be replaced.

When reinstalling or replacing the cooler, make sure to work the charge air cooler hoses all the way onto their connections. Torque the spring-loaded clamps with a torque wrench to the torque specified in your owner’s or factory repair manual.

Similar checks need to be made of the A/C condenser and radiator. Thoroughly reverse flush all these cores with water or air to ensure cleanliness of the fins and full air flow. A less efficient A/C condenser will make the system less efficient, increasing cooling system load.

Blake also suggests a check of the turbo variable geometry actuator or waste-gate and replacement of any worn linkages. And check the condition of the air cleaner or, if you have a restriction gauge, make sure restriction is within limits. If dirty, replace it because an increase in airflow will help the engine run cooler.

Radiator condition
Mike Masuch, of Mike and Daughter’s Radiator Aid, points out that radiator fins are thinner than ever – so thin a high wind may even bend them. While that charge air cooler is off, check the condition of fins and straighten with a fin comb, if necessary. This will help airflow. Fins on the radiator, as well as those on the charge air cooler and A/C condenser, are subject to corrosion from today’s road salting chemicals. So are the bolts that hold the tanks on. Flushing these heat exchangers with pressurized water in winter as soon as you can after running down treated roads will preserve their performance and life.

Masuch says fins that have corroded away will raise the engine’s operating temperature slightly. That, in turn, will raise system operating pressure and temperature and gradually cause damage to radiator tank tabs or even the main tank structures. Keep those critical cooling fins clean and have a radiator re-cored at the first sign of fin deterioration.

Check mounts for tightness and the condition of any bushings. Replacing bushings that are cracked or crushed down will help minimize vibration and radiator mechanical damage, which can sometimes crack soldered connections.

It’s smart to inspect your radiator core from the inside of the top tank by removing the cap or disconnecting the upper radiator hose and using a flashlight. Always allow the cooling system to cool to well below operating temperature before trying to remove the cap. Grab the cap with a heavy rag and rotate it slowly counter-clockwise to the first stop to relieve pressure. Once pressure is relieved, depress it and rotate farther to remove.

Always allow the system to cool and then drain a couple of gallons of coolant into a clean pan before attempting to disconnect the upper radiator hose. It may also be helpful to drain coolant to get a better look at the radiator tubes. They should be clear of corrosion, offering a completely open passage. If not, drain the system, disconnect and remove the radiator, and take it to a radiator shop for chemical cleaning and a checkup. Partially clogged passages will start a process of deterioration bound to result in failure of a tank seal or other part down the road as pressure and temperature build.

It would also be smart to check (or simply replace) the radiator cap, especially if you have seen signs of coolant forcing its way out of the overflow tank when the engine is hot. Allow the engine to cool, remove the cap, wet the seal and test with a cooling system pressure tester to make sure it holds rated pressure – usually 15-18 psi. Also replace if the seal is cracked or heavily grooved.

Check for coolant leaks
Caterpillar’s Powers also suggests checking for leaks at all hose connections and joints, and plugs installed in the block. Replace hoses that are soft, cracked or bulged out. This includes the long hoses running to the heater core. Turn off the water valves to the heater core once the weather has turned warm, and inspect the connections to the shutoff valve and the valve itself for leaks, replacing parts or tightening clamps as necessary. If you have an APU, check all hoses leading back and forth to the APU and tighten clamps or make repairs as necessary.

Tighten or replace defective clamps, and remove and reseal plugs after draining the system, as necessary.

The thermostat
Detroit Diesel’s Chuck Blake says the thermostat is normally working properly unless there are “coolant temperature swings out of normal ranges.”

A thermostat that is working right will cause the engine to warm steadily until it hits a certain temperature that will vary little. Operating temperature will normally rise slightly during warmer weather or when climbing long hills with the engine under heavy load, but only 10-15 degrees except under extreme conditions.

If the operating temperature drops to below normal, the thermostat is bad. If the engine begins to warm to a higher than normal temperature before leveling off, or the engine suddenly begins to run very hot, and the fan is coming on, chances are very good that the thermostat has failed.

“The thermostat should ideally be replaced every year or two, anyway,” says Shawn Sholly, president of Mike and Daughter’s Radiator Aid. “Maximum life is 5-7 years.” She recommends using only an OEM unit, as some aftermarket units may be unreliable and not keep the engine at the proper temperature. Always use new gaskets and seals with the thermostat.

The cooling fan
Fan clutches take a lot of abuse. According to Blake, wide temperature swings are also a sign of the fan clutch operating improperly. You’ll note that the engine temperature when it cycles on and off will change if it has its own sensor that has begun to fail. If this occurs, replace the sensor.

“Inspect the fan clutch for rust dust streaks, possibly indicating clutch wear,” Blake says. “Check the air supply line, making sure it is intact (no cracks or rubbed areas) and replace it if necessary.” Check the connections at either end to make sure they are tight.
A worn clutch would be indicated by an obvious reduction in noise due to slower-than-normal fan speed during fan operation. This would be accompanied by engine overheating on steep hills during long climbs, or in traffic in warm weather. Also, a fan clutch that is extremely hot to the touch right after shutdown would indicate slippage.

Fan clutch makers supply rebuild kits designed to restore full power. If necessary, rebuild the clutch or take it to an engine or truck dealer for rebuilding.

Blake also recommends checking the condition of the baffles and radiator seals designed to prevent radiator discharge air from recycling to the front of the radiator. Also look at the fan shroud – does it fit the fan evenly all the way around, and is it securely mounted and in good condition? Effective shrouding greatly increases the ability of the fan to move air through all the heat exchangers, so replace any of these parts that is defective.

Belts and tensioners
Inspect the belts to make sure they are free of cracks (the inside surfaces usually crack first). Also, traditional Vee-belts will develop a glazed surface along both sides of the Vee if they have been slipping or have reached very high miles. Replace belts that are cracked or glazed.

Traditional belts should always be tensioned with a tension gauge, available for minimal cost at a heavy-duty distributor or dealer. Tighten all adjusting and mounting bolts till snug. If an accessory is not properly lined up so the belt runs crooked, tighten or repair mounting systems to correct.

Most trucks today use serpentine belts with an automatic tensioner. Test the function of the tensioner by first rotating to loosen and remove the belt. Then rotate the tensioner back and forth slowly through its entire operating range. Rotation should be smooth and steady. If it binds or makes noise, the bearing or spring has likely failed, and it should be replaced.

The coolant
Spring would be an ideal time to get your coolant analyzed by a laboratory. Your engine dealer can help you find a good one. Lab tests will reveal a hard-to-discover problem, like mixing of different types of antifreeze.

“Mixing antifreeze is a problem,” Sholly says. “You just can’t mix the different types. Corrosion often occurs from the inside out. This happens because of neglect of the antifreeze. Take care of the coolant!”

There are two ways of doing this. You can use ELC (Extended Life Coolant) and add only ELC when you have leakage or evaporation, plus adding a bottle of extender in the middle of each change cycle. Or you can use more traditional methods.

The best of the traditional methods is the use of only Fully-Formulated TMC RP-329 Type A coolant – you’ll see this designation on the jug. It contains full cooling system protection. Combine this with some sort of coolant filter that provides a controlled release of SCAs (Supplemental Coolant Additives). The best ones actually adjust the rate at which they add SCAs to the conditions and last more than 100,000 miles.

The SCAs are necessary to keep system protection topped off as the anti-corrosive chemicals in the original antifreeze wear out. You need to test for SCAs at your routine maintenance intervals with this type of protection. But, if you use only the Fully-Formulated coolant and the right SCA-adding filter, you’re likely not to need to add SCAs.

Either of these systems will extend coolant life to at least 600,000 miles with full protection if you add only the right coolant consistently and keep up with necessary filter changes to add those SCAs, or the extender. Keeping the right antifreeze with you in the truck and adding only that is the most important key to making either system work.

Make sure to keep the antifreeze at a 50/50 concentration unless you live in an extreme northern climate, where 40/60 is allowed. Test with a refractometer – a device that reads the level of either type of glycol with light. The best thing is to buy and add only pre-mixed 50/50, which has de-mineralized water to help the additives work. Be careful not to allow the antifreeze concentration to get too high by repeatedly adding straight antifreeze. Sholly says, “Too much antifreeze is like a gel.” The right mix of water and glycol will make the engine run much cooler.

If you don’t maintain the coolant, you can have serious damage to the engine itself. Radiator leaks are also common because untreated coolant acts like an acid. Bad coolant will also clog the tubes, which is one of the classic causes of overheating. Even minimal clogging will gradually lead to higher and higher system pressures and deterioration of the radiator and other parts.

Check how many miles are on your coolant. Add a bottle of extender if you’re using ELC and you’ve reached the recommended mileage. If your coolant has reached the specified maximum life, or if the lab tests indicate a problem, flush and refill the system with either ELC with no filter, or Fully Formulated with the right filter.

Clean coolant in a system that’s been properly flushed, heat exchangers that are clean on the outside, and a fan drive system that is in good condition will carry you through summer’s heat with little to worry about.

For more information:
Mike and Daughter Radiator Aid
(717) 394-0184

Caterpillar Engine Div.
(309) 675-1000, click engines

Detroit Diesel Corp.
(313) 592-5000

Cummins Filtration
(615) 367-0040

The Penray Companies
(800) 322-2143

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