How To Help Your Radiator Keep the Engine Cool

1: Before starting, we gathered the two types of cleaners and pump-up adjustable sprayer.

E. Don Smith
December 5, 2012
Filed under Resources

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.

Step 13:

13: When you finish the job the radiator should be nice and clean like this one and ready to keep your engine cool no matter how steep the grade. And you just saved yourself more than $1,000.

Step 12:

12: After you think you have the radiator assembly properly rinsed, start the engine and you will likely see soap bubbles as the fan pushes a huge amount of air through the radiator and charge air cooler. If this happens then rinse, rinse and rinse again.

Step 11:

11: Just as with the other cleaner, the final step is to completely rinse the radiator stack. In this photo we are showing the proper fan spray using a hose end spray nozzle. This method is actually more effective at rinsing but you must refrain from using a jet of water or you will damage the fins. Some owners also report successfully rinsing from both sides of the radiator, but if you do this, prepare to get wet since you’ll be lying on the ground.

Step 10:

10: If you decide to pursue the aerosol coil cleaner method, spray the cleaner over the entire area of the radiator and you will start to see the foam appear on the surface. The foam will actually push the dirt and debris out of the radiator because of the mechanical action of the expanding foam. Since there isn’t an extension hose as with the pump-up sprayer, using aerosol cans makes spraying the other side of the radiator/charge air cooler more difficult. If you have access to safety jacks (don’t rely on the leveling jacks alone) you can use them to raise the coach before crawling under to get better access to the other side, which is the dirtiest part.

Step 9:

9: After the solution has sufficient time to clean, we rinsed it completely off using a water hose, as shown here. This method prevents any damage to the coils. Plan on spending a lot of time rinsing to ensure all the dirt and cleaner are removed from the radiator. If the radiator is not clean, repeat the process one or more times until the residue is gone.

Step 8:

8: After spraying the cleaner on both sides of the radiator/charge air cooler stack, you will see it foam up inside the coils and start to dissolve the oil and debris trapped inside the fins. Allow the solution to soak for several minutes but don’t allow it to dry on the surface. (Follow product directions if using something different.)

Step 7:

7: From the driver’s side we removed the air filter access panel and sprayed again from this angle. It may not be possible to reach every square inch of the radiator/charge air cooler, but if you spray both sides and allow the cleaner to run from the top down you will eventually get it all covered with the degreaser spray. If you have easy access to the engine bay from the bedroom, this is another great location to use for spraying the degreaser chemical onto the radiator.

Step 6:

6: Next, after blocking the wheels for safety, we crawled under the rear of the coach on the passenger side and sprayed the radiator stack from this angle as much as we could. The radiator fan is in the way so you will have to change the position of your sprayer to reach as much of it as possible while realizing that in most coaches you may be spraying the charge air cooler or air conditioner coil and not the radiator directly.

Step 5:

5: After adjusting the sprayer nozzle to produce a fan/wide-angle spray, we then completely covered the entire surface of the radiator.

Step 4:

4: Following the directions on the cleaner, we diluted it 50/50 with water in the pump-up sprayer.

Step 3:

3: If you often travel on dirt roads, your radiator could end up looking like this. Fortunately ours did not, but don’t be surprised at what you will see once you crawl under there.

Step 2:

2: Look under the rear cap of the coach to visualize the position of the radiator/ charge air cooler assembly so you can reach it with the sprayer. We also removed the air filter access panel on the driver’s side of the coach so we could spray from two different angles.

Step 1:

1: Before starting, we gathered the two types of cleaners and pump-up adjustable sprayer.

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 (, 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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One Response to “How To Help Your Radiator Keep the Engine Cool”

  1. Michael Grudt on December 20th, 2012 1:51 pm

    Good article. I use a biodegradeable cleaner called “Breeze”, and it works wonders on aluminum mesh screens in oven and microwave vents. It also works on stubborn grease residues on painted cupboards and without harming the surface. It is also great on engines and radiators. I buy it by the gallon and it lasts a long time. I got mine at a local hardware store, although you have to look for it. I use it straight without mixing it with water and it doesn’t take much to do the cleaning.


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