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Coolant Flushing For Cummins ISC 8.3 That Requires SCA Coolant

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I have a 1999 American Dream with a Cummins ISC8.3 diesel engine. It requires SCA type coolant. I've seen postings that indicate there are ELC (extended life) coolants that don't need to be tested as often as the standard types. Is a thorough flushing of the cooling system required to change from one to the other? And in general, what is the procedure to do a coolant change/system flush on an engine like this?

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There are no differences in Caterpillar or Cummins engines coolant requirements/both have the same mil specs for coolant requirements. Also, Caterpillar ELC or Fleetguard equivalent have the same characteristics-- OAT-based coolant with no need to check or add SCA.

BTW, neither Caterpillar nor Cummins "require" an SCA type coolant. The correct statement is: Low silicate for diesel coolant with added SCA that is routinely tested and SCA level replenished" is an acceptable coolant. The new generation OAT-based coolants are also approved and both Caterpillar and Cummins (Fleetguard)-- both sell it. The advantage of the OAT-based coolants is that there is no need to ever test or add SCA and instead of the common 3 year coolant life, at least Caterpillar ELC (and likely true for Fleetguard product as well) have a 6 year life WITH NO MAINTENANCE in an RV application. Even in OTR trucks they have a 6 year life, with an added extender after 3 years/300,000 miles.

Could you use a Cummins coolant in a Caterpillar or Caterpillar coolant in a Cummins-- I guess so, but my recommendation would be to use the OAT-based coolant marketed by YOUR engine manufacturer. That way, if you ever have it in for engine service, they will have the correct coolant.

Here is an article I wrote a on the "proper" process to switch from "standard low silicate for diesel coolant with SCA" to Caterpillar ELC. Again, the steps for a Cummins would be the same:

Cooling System 101

I just changed out my coolant and replaced all water hoses and belts. Thought I would share the experience.

To my knowledge all RV manufacturers use a “low silicate coolant for diesels” 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 need 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 cooling system, NOT when purchased) or testing reveals an 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.

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 system capacity of distilled water for a final flush plus final fill (50%). Also a good idea to change the engine thermostat and thermostat gasket as these are a wearing component and it involves very little more work while you are there. I know Caterpillar recommends thermostat (they call them regulators) every 3 years.

Turn dash heater to full hot for the rest of the procedure—fan off. With the engine cold or at least cool, drain coolant. On some, there is a drain ****. On others, pull the lower radiator hose. Two Rubbermade 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 cooling system with tap water. IMPORTANT: Be sure to remove any air lock 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 engine to warm up (using the cruise control to select 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 engine to cool, drain and again flush until 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 clear. Run the engine to 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 last rinse). Same for thermostat(s).

Last Rinse is 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 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 rear or side radiator. On rear radiator, most if 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 coach). If it is just dirt, a hose and regular nozzle is all you need. If greasy or oily, use Joy liquid (dish washing detergent) in a spray bottle. Be SURE to rinse it off completely. You need to insure 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.

Check belts while you are in there.


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