[Drake]

At my shop we had problems with certain coolants causing more electrolysis than others. It might pay to try some different types of long life coolants. Everybody seems to have a little different recipe. We had a lot of trouble with Toyota Tundras and 4-Runners until we switched over to factory Toyota coolant. One customer was getting pinholes in his radiator inside of 3 months using the Sierra brand of coolant. We had been using that brand for years without problems. It's one of the recommended brands for VW because of the type of aluminum alloys they use. We had checked the grounds which were ok.We had to replace 2 radiators before a friend at a radiator shop suggested using a different coolant.