Haven't seen that particular problem YET. How old are these units? Do they have the russian radiators? Is the coolant red? Probably Fleet brand coolant. How old is the coolant? Have you taken a DCA/Sca test strip on the coolant to check the ph level? Are you seeing any white powdery corrosion? Looking forward to a resolution to this mystery.
The units have a mfg. date of 08. but were not put into service until 09. So far they are the ones with the Russian radiators. The coolant is the factory coolant as they are just now hitting 2 years old and haven't been changed yet. The problem I have had so far is a crystal build up on the goose necks on the block. The build up swells the hose to the point the clamp cuts the hose. Have been told that it is due to a cheap aluminum mix in the plate with the goose necks but Generac nor JD will admit to a mfg. defect. The hoses are clean as the day they left the factory on the radiator side.