There appears to be a problem with "long life" or "extended life" coolants used in Cummins engines.

Apparently the "carboxylate" organic acids in these coolants are damaging the silicone seals used in Cummins cooling systems. One source (not at Cummins) claims there have been more than $4 million in warranty claims. In late June, Cummins sent a letter to truck manufacturers and distributors warning against the use of these coolants.
"Based on available data, Texaco's Extended Life Coolant and other similar formulations supplied by Equilon Enterprises, LLC, an affiliate of Texaco, should not be used in Cummins engines," says the letter. Cummins specifically identifies Texaco Extended Life Coolant and its derivatives, marketed by Caterpillar as Cat Extended Life Coolant, by Shell as Rotella Extended Life Coolant, and by Detroit Diesel as Power Cool Plus.
"These organic acid coolants appear to cause degradation of the silicone seals after 80,000 to 100,000 miles," the Cummins letter says. It recommends replacing such coolants immediately with a recommended conventional coolant.
"This action will not affect the Cummins warranty, but failures attributable to the use of these coolants will not be the responsibility of Cummins Engine Co.," the letter says.
Cummins and Equilon will be reviewing the compatibility issue further. Cummins says it intends to support Equilon in the development of a solution. In the meantime, Equilon continues to recommend and support the use of its coolants in all other diesel engines.
Only International has been using extended-life coolants as a first-fill on its assembly lines with Cummins power. It stopped using these ELC factory fills as of July 12. Most other truck builders offer extended-life coolants as an extra cost option on new vehicles.
For more information, see Jim Winsor's column in the August issue of Heavy Duty Trucking.