It's probably not a diesel rated coolant...meaning it doesn't have SCAs or DCAs (supplemental or diesel coolant additive) which is specifically added to reduce the detrimental effects or cavitation in diesel engines. If you don't know I'm talking about, use your favorite search engine and search for "diesel cavitation" and you will have plenty of interesting reading. This is not a problem that happens overnight or even after 20,000 miles...it takes a while but when it does happen the affects will ruin the engine. It's a long term insurance policy.
If you want to know if the coolant is rated for diesel engines...it will say so on the bottle. It will also say made for heavy duty trucks or engines. Not light duty trucks. Also look for the specifications on back of the bottle from engine manufacturers or ASTM (see attachment).