immrchevvy

I recently sold my 1996 Lumina APV. It has the 3.4 V6 and the 4t60e transmission. The person who bought it just called me and told me that he was driving it and the temperature hand was going up real high, then it would come down, then go back up. He says there is water in the oil now and that they have "lost" three gallons of coolant in the motor. Heasked me what I am going to do about it. I sold it as is. I never had a problem with this van the whole time I owned it. He hashad it 1 month and has had 2 problems already. I don't know what to do. Any suggestions?