by Brett Wolff
Cooling System 101– the step by step on properly replacing coolant.
Wrote this for the Caterpillar RV Engine Owners Club, but most will apply to other applications:
I just changed out my coolant and replaced all water hoses and belts. I thought I would share the experience.
To my knowledge, all RV manufacturers use a “low silicate coolant for diesel” with included or added SCA. Coolant needs to be changed per manufacturer’s instructions (usually every 3 years). Additionally, the SCA, pH and freeze point needs to be checked on regular intervals using SCA test strips and SCA added as needed. The test strips are inexpensive and easy to use. When either the time lapses (time starts when coolant is installed in the cooling system, NOT when purchased) or testing reveals out-of-line conditions like pH or freeze point, it is time to change it. You can avoid all the testing and SCA adding, and go to 6 year change intervals by going to an Extended Life Coolant and get 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 RIGHT, but low-tech.
The first step is to determine your total cooling system capacity. Your chassis maker or coach maker, not your engine manufacturer is the proper source. Then buy enough coolant (concentrate, not pre-dilute) to make up 50% of that volume. If going back with a 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 final fill (50%).
Turn dash heater to full hot for the rest of the procedure—fan off. With the engine cold or at least cool, drain the coolant. On some, there is a drain cock. On others, pull the lower radiator hose. Two Rubbermaid 10 gallon storage bin lined with black trash sacks so they don’t get dirty work well. At the end of the whole process, use a coffee can and funnel to pour old coolant into new coolant/water containers for recycling. Our city maintenance shop recycles coolant for free.
Refill the cooling system with tap water. IMPORTANT: Be sure to remove any airlock from the thermostat housing. Some systems have a hose set up for this—on ours, I just loosen the coolant line to the air pump and bleed the air out. Allow the engine to warm up (using the cruise control to select the idle speed of 1,000-1,100 speeds this up). Run for about 10 minutes at regular temp. If the temp gauge does not rise as normal, you likely have an air block and need to bleed the thermostat housing. Allow engine to cool 20-30 minutes and drain again. Repeat until the effluent color is clear.
At this point, if this is the first coolant change on a 2-3-year-old coach and you are not changing coolant brands/types, skip right to “Last rinse”. For older systems or when switching types of coolant, add a Cooling System Cleaner. Follow the directions. Run, allow the engine to cool, drain and again flush until the effluent is clear. The flushing is markedly sped up by pulling off the heater hose (usually 5/8” to ¾” lines) going to dash heater/motor-aid water heater, etc from the water pump. Put a hose nozzle in the hose and let it run until it comes out clean. Run the engine to the temperature at least once with tap water.
If your hoses are over 3-4 years old, this is a good time to change them as well (before the last rinse). Same for thermostat(s).
Last Rinse it with distilled water. At $.62/gal at Walmart, it is silly to skip this step and leave your system full of high-mineral content water (there will be several gallons of residual water that you can not easily remove). Run the engine for 10 minutes after getting to 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 PRE-DILUTE) to make 50% of cooling system capacity. So for a cooling system with 20 gallons capacity, add 10 gallons of Coolant CONCENTRATE (plus 1/2 overflow container capacity). Top off with distilled water to achieve your 50/50 mixture—it doesn’t matter if you only have to add 1 gallon or 10 of distilled water, you KNOW you have the proper 50/50 mixture.
This is also a good time to clean the OUTSIDE of the radiator/after-cooler whether you have a rear or side radiator. On the rear radiator, most of the debris will be on the FRONT of the after-cooler (accessed from under the bed). On side radiators, most debris is on the outside of the after-cooler (side of the coach). If it is just dirt, a hose and regular nozzle are all you need. If greasy or oily, use Joy liquid (dishwashing detergent) in a spray bottle. Be SURE to rinse it off completely. You need to ensure that the perimeter is as clean as the center. Ya, I know it is easier to see the center, but the fan blades “sling” the dirt to the perimeter.