Tips for keeping the cooling system free of the dirt and grime that can impact its efficiency.
By Brett Wolfe, F252125
By its very design, the cooling system on motorhomes equipped with a rear radiator tends to clog up fairly quickly. Imagine the amount of dirt stirred up from the road by a 40-foot motorhome with its six tires driving at highway speeds. That dirt-filled air then passes over the hot, sometimes oily, rear axle, transmission, and engine before it is sucked up by the cooling fan and forced through the aftercooler and then the radiator. No wonder this cooling equipment becomes clogged. Driving in extremely dusty environments will accelerate the problem. At a minimum, all coaches with rear radiators need to have their aftercooler cleaned once a year.
Most rear-radiator motorhomes have a sandwiched cooling system, with the aftercooler first in line (closest to the engine) and the radiator behind it (toward the rear). Note: the aftercooler, intercooler, and CAC (charge air cooler) are different names used for the same device, which serves as an air-to-air radiator between the turbocharger and the intake manifold. Very few coaches have a stacked aftercooler and radiator.
The vast majority of dirt will be on the front side of the forward-most component in the system, since cooling air flows from front to back. This would be the aftercooler. The problem with a sandwich-type cooling system, however, is that there is no way to effectively clean the front of the aftercooler from the outside rear of the motorhome.
You may be tempted to use a pressure washer, increasing the water pressure enough so that the stream will go through the radiator, air gap, and aftercooler with the necessary force to knock off dirt and grime from the front of the aftercooler. Doing this would most certainly bend the radiator fins, so do not do it.
The only safe and effective way to clean the aftercooler is from inside the motorhome, with access to the engine gained through a panel located in the bedroom or a rear closet. Shine a strong flashlight inside the fan shroud, between the fan blades. The fan blades will “sling” the dirt toward the perimeter, so verify that the perimeter is as clean as the center. If it is just dirt, a hose with a regular spray nozzle is all you need. If you find the dirt to be greasy or oily, saturate the areas with dishwashing detergent in a spray bottle and allow the cleaner to soak in before rinsing it off completely.
While you have the engine cover open and are getting dirty, check the condition and tension of all belts. And it may be time to change the engine coolant and thermostat(s) as well (three years is the normal change interval for regular low-silicate coolant for diesels with added SCA).
All diesel engines (Caterpillar, Cummins, etc.) built prior to January 1, 2007, were designed to have the crankcase vent to the atmosphere. However, if this vent is in front of the air intake for the cooling system, it will put oily vapor as well as dirt into the front of the aftercooler. For less than $12 you can purchase a blow-by tube that attaches to the vent and can be extended to behind and below the fan shroud intake, eliminating the discharge from the crankcase as a source of cooling system contamination. Verify that the extension tube remains fairly straight from the engine, with no dip, loop, or sag in the tube. One of the by-products of combustion is water vapor, which can freeze if allowed to collect in the extension. Should the extension tube become clogged and block normal crankcase venting, serious engine damage could result.
Also, make sure that you are not overfilling the engine oil, as excess oil is expelled via the crankcase breather.