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How To Help Your Radiator Keep the Engine Cool

Originally Published in MotorHome Magazine

As you drive your motorhome, the engine generates a tremendous amount of heat. A quick walk behind a rear-engine diesel coach while it’s idling is all it takes to better understand how much heat is produced during operation.

The law of conservation of energy teaches us energy cannot be created or destroyed; however, it changes form and flows from one place to another. As the fuel is combusted, most of that energy moves the motorhome down the road and a smaller portion of that energy generates heat inside the engine. In order to sustain this process, that heat has to be removed from the engine block or the engine will overheat and fail. Some of the heat is lost through the exhaust, but it’s the cooling system that removes most of the heat.

There are passageways inside your motorhome’s engine where the coolant flows. Located in strategic areas, these passageways maximize the cooling effect and make sure the engine’s key components are cooled in combination with the engine oil. It is the job of the water pump to circulate coolant through those areas, which helps pull the heat from inside the engine and move it to the radiator. Smaller gasoline motorhomes have a total coolant capacity of only a few gallons, while a large rear-engine diesel coach could hold more than 15 gallons of coolant.

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During engine operation, the thermostat opens at a specified temperature, which allows the coolant to circulate from the engine and then to the radiator where the real heat exchanging takes place. Once the hot coolant reaches the internal core of the radiator it starts a dramatic cooling process to prepare it for another trip back through the engine. As the heated coolant enters the radiator, a high-capacity fan in front of or behind (depending on engine location) the radiator forces air through the thousands of cooling fins in the radiator. The tiny fins in the radiator create a tremendous amount of surface area, which allows the heated coolant to dissipate its heat into the atmosphere in combination with the airflow of the engine fan.

On a rear-engine diesel motorhome with a rear-mounted radiator (not side radiators) a unique situation makes cooling a bit of a challenge. Since the engine is in front of the radiator (unlike your car) and in the rear of the coach, the cooling fan has to push the air out of the engine compartment across the radiator to keep it cool. In doing so anything dirty originating from the engine bay gets blown into the radiator. Many rear-engine diesel motor-homes also have a charge air cooler and an air conditioner condenser coil stacked along with the radiator, making it even more difficult to clean and inspect.

Some diesel engines have what is known as a crankcase vent or “slobber tube” that, unless properly positioned, will vent its contents into the radiator stack. On newer coaches these have been relocated or redesigned because of increased EPA regulations and this is not an issue. On many older models, however, the tube is vented in front of the radiator. Any residue that is passed through the radiator will start to build up on the fins and over time reduce the efficiency of the radiator to transfer heat from the hot coolant inside to the cooler atmosphere outside. The result is an engine that will run higher operating temperatures until it finally overheats, which is usually in the summer while climbing hills. If your diesel coach has side radiators, they pull air from the outside of the coach in and across the radiator fins so the dirt (not much oil) on them is mostly on the outside, making their cleaning even easier.

The good news is this is a common problem and one that is fairly easy to solve with a little time and some good cleaning products. If you take your motorhome to a repair shop you may be told the best way to clean a dirty radiator/charge air cooler is to remove it and clean it outside of the engine bay. They are right. Once outside the engine bay, both sides of the radiator (and charge air cooler) can be sprayed with the proper chemicals to degrease and clean them. That is very expensive, however, and can easily cost more than $1,000 on a rear-engine diesel coach.

If you don’t mind getting a little wet and dirty, you can handle the cleaning – if the fins aren’t completely plugged up with dirt and oil – using one of several environmentally friendly products. There are a few things you should know before you get started, so make sure you read the entire article before you begin.

One of the first cautions is that although many of the automotive cleaners on the market are biodegradable and nonhazardous, they are not suitable for the aluminum of your radiator. In addition, the high alkali (caustic) cleaners sold at the typical auto parts stores and big box home stores are also not suitable for aluminum. Prolonged exposure to these caustic cleaners will etch or discolor aluminum so they should not be used. 

The HVAC system of your house may have an outside coil that is similar to an RV radiator; therefore some of those cleaning products (coil cleaners) may be safe for use, but check the label or look online to make sure it is labeled for use on aluminum. We picked up a few cans of Frost King Air Conditioner Coil cleaner at Walmart as an example of the many coil cleaners that are on the market. This one is even labeled as safe for automotive radiators.

Another caution is when you are spraying water and rinsing the radiator you must use a gentle spray or stream of water to prevent damaging the radiator fins. If you use a high-pressure jet the tiny fins of the radiator will be bent and actually reduce the airflow of the radiator, which is the exact opposite of your goal.

Although the chemicals we used are safe and solvent free, the residue you remove from your radiator will contain some oil in addition to typical dirt and road grime, so be sure to perform this operation in an area that is not affected by the runoff.

Another important reason to use the correct chemicals is that other parts of your motorhome and engine will also be exposed to the cleaning spray during this process. 

We selected Extreme Simple Green (www.industrial.simplegreen.com), which is specifically made for aircraft aluminum and designed to cut through oil and grease without causing any damage to the fins or the surrounding rubber, plastics and painted surfaces. 

This product was impossible for us to find locally, but it can be ordered online. Do not let the local auto parts store tell you that using other caustic “purple” cleaners or even standard Simple Green are just as good. Yes, they will clean well but they will also etch the aluminum and leave a bad looking surface. If it’s not listed on the label, the product is most likely not safe for aluminum use. The Extreme Simple Green we used was $28 a gallon plus shipping so it’s not expensive and we even had some left over after this project.

Other than the cleaner, you will also need access to a water hose and a pump-up sprayer to dispense the cleaner onto the radiator. If you decide to use an aerosol product, make sure you have several cans as the radiator is quite large and you need to clean from both sides. Once you gather your supplies, block out an hour and a half to two hours of your day and you are ready to perform a DIY adiator cleaning just as we did with no other special tools needed. It is also a good idea to add this to your list of service items once every year or two. 


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