antifreeze

maintain the cooling system on a 3126 just like a engine with wet liners with extended life coolant (ELC) or with the proper nitrite concentration do not mix one with the other wrong coolant can and will cause the block to erode just like a wet liner

The test strips are normally reserved for use on diesel engines with cylinder liners or otherwise known as wet liners. The cat 3126 engines commonly found in motorhomes are not lined engines. The whole thing can be avoided tho by using high mileage 50/50 mix antifreeze. The 50% water is deionized water. All of the antifreeze manufacturers offer a high mileage 50/50 product for over the road use.
Regarding the test strips you can use them to if you want to. Be aware that they do have a shelf life.

what other post? Cummins, not Cummings.