Replacing the coolant at recommended intervals and maintaining the system helps to ensure trouble-free travel.
By Brett Wolfe, F252125
I just changed the engine coolant and replaced all the water hoses and belts in my diesel-powered motorhome and thought I would share the experience.
To my knowledge, all RV manufacturers use a low-silicate coolant for diesel engines with supplemental cooling additive (SCA). The coolant needs to be changed per manufacturer’s instructions (usually every three years). Also, the SCA, pH, and freeze point need to be checked at regular intervals using test strips, and more SCA should be added as needed. The test strips are inexpensive and easy to use. When the replacement interval is reached (the time starts when the coolant is installed in the cooling system, not when the motorhome is purchased), or when testing reveals that the pH or freeze point is not at the proper level, it is time to change the coolant. You can avoid all the testing and SCA adding by switching to an extended-life coolant that allows six-year change intervals and better cooling system protection as well. Whichever coolant you choose, most of the steps are the same. The job is reasonably time consuming to do correctly, but low-tech.
The first step is to determine the total capacity of the cooling system. The chassis maker or coach manufacturer — not the engine manufacturer — is the proper source. Buy enough coolant (concentrate, not prediluted) to make up 50 percent of that volume. If your system uses coolant that requires additional SCA, purchase that as well. Also purchase 1.5 times the system capacity of distilled water for a final flush plus the final fill (50 percent).
When you are ready to begin, turn the dash heater to the highest temperature setting with the fan off for the rest of the procedure. With the engine cold or at least cool, drain the coolant. Some cooling systems have a drain petcock. On others, you will need to detach the lower radiator hose. I suggest using two 10-gallon plastic storage bins — lined with black trash bags so they don’t get dirty — to collect the used coolant. At the end of the entire process, use a coffee can and a funnel to pour the old coolant into the now-empty new coolant/water containers for recycling. Our city maintenance shop recycles coolant for free.
Refill the cooling system with tap water. It’s important that you remove any air lock from the thermostat housing. Some systems have a hose set up for this — on my motorhome I just loosen the coolant line to the air compressor and bleed the air out. Allow the engine to warm up. Using the cruise control to select idle speed of 1,000 rpm to 1,100 rpm will speed this up. Allow the engine to run for approximately 10 minutes at regular temperature. If the temperature gauge does not rise as normal, you likely have an air block and need to bleed the thermostat housing. Allow the engine to cool for 20 to 30 minutes and drain the system again. Repeat until the effluent color of the tap water being drained is clear.
If this is the first coolant change on a 2-year-old to 3-year-old motorhome and you are not changing coolant brands/types, skip right to “Last rinse.” If your motorhome is older or if you’re switching the type of coolant used, add a cooling system cleaner. Follow the product’s directions. Run the engine; allow it to cool; drain; and again flush the system until the effluent is clear. The flushing can be markedly sped up by pulling off the heater hose (usually 5/8-inch to 3/4-inch lines going to the dash heater/motor-aid water heater, etc.) from the water pump. Put a nozzle in the hose and let it run until what comes out is clear. Run the engine to temperature at least once with tap water.
If your hoses are more than 3 or 4 years old, this is a good time to change them as well (before the last rinse). The same holds true for the thermostat(s).
The last rinse should be done with distilled water. Since distilled water costs less than $1 a gallon at big box stores, it is silly to skip this step and leave your system full of high-mineral water (there will be several gallons of residual water that you cannot easily remove). Run the engine for 10 minutes after it reaches operating temperature. Cool and drain. Also drain and flush your coolant overflow container and refill with new coolant/distilled water.
Add the proper amount of coolant concentrate (not prediluted coolant) to make up 50 percent of the cooling system capacity. A cooling system with a 20-gallon capacity would require 10 gallons of coolant concentrate (plus fill the overflow container halfway). Top off with distilled water to achieve your 50-50 mixture. It doesn’t matter whether you have to add 1 gallon or 10 gallons of distilled water; by combining the coolant and water in this fashion, you will know you have the proper 50-50 mixture.
This is also a good time to clean the outside of the radiator/aftercooler, whether you have a rear or side radiator. On a rear radiator, most of the debris will be on the front of the aftercooler (accessed from under the bed inside the motorhome). On side radiators, most debris is on the outside of the aftercooler (on the side of the motorhome). If it is just dirt, a hose and regular nozzle is all you need. If you find greasy or oily buildup, use a solution of dishwashing detergent mixed with water in a spray bottle. Be sure to rinse it off completely. Simple Green and others offer products that are safe for cleaning aluminum aftercoolers and radiators. You need to ensure that the perimeter is as clean as the center. It is easier to see the center, but the fan blades “sling” the dirt to the perimeter.
While you’re in there, make sure to check the belts as well.
Performing these maintenance routines should help you and your motorhome to keep your cool.