Hey guys. I have a Ford 1900 tractor, with a 3 cylinder Shibaura diesel engine. It's an 1980 - 82 model. I don't use it a whole lot, maybe an hour or 2 a week. Sometimes longer, just depends. Anyways, early this summer I did an OC, and put in Shaeffers Supreme 7000 synthetic blend oil. It seemed like every other time that I checked it, I was a quart low. I presumed that the oil was too thin. Anyways, I changed it out about halfway through the summer to Rotella T 15w-40. Hasn't seemed to used hardly a drop since. I was semi-amazed. I didn't thing there was that much difference in the viscosity to see a difference. Okay. Question one - winter is soon here. Should I change it back to the 5w-30 for winter? Or keep the 15w-40 in it? Another question. When should I do OCI's on it? Every 6 months? Every so many hours? Thank you all.