Switching a high mileage motor to synthetic with no preparation is kinda risky. Since they are so good at cleaning up junk they can dislodge pieces of carbon and stic them places where they shouldn't be, like in our piston cooling jets. Oldmisterbill had this happen on one of his engines after a switch to synthetic with not so good results. Don't get me wrong I love synthetics. I switched my truck to amsoil at around 205,600 on the clock. I used the auto-rx treatments, 1 treatment followed by a normal oil rinse cycle followed by another treatment with regular oil, followed by another rinse with mineral oil. Altogether from inception to the synthetic switch it was about 8 months and 4 oil/filer change cycles. Even at that I realized it was an experiment and had the whole thing blown up there would have been no ill will towards RL or Amsoil or even Auto-Rx. I did it in the understanding that it was an experiment. Now the jury is still out on the results, but at least I didn't blow anything up or have massive oil leaks. I still have good oil pressure. Oil consumption may be slightly improved, but I still have a fair amount of blowby. Not terrible but certainly noticeable. I can't wait to see what Caterpillar's oil analysis says about the wear numbers. I pay careful attention to oil analysis but don't take it as the gospel truth. I've seen people get a clean bill of health with oil analysis and then throw a rod and other people, myself included get a very alarming oil report and then have many relatively trouble free miles ahead. I think the 5W-40 would be a little thin for anybody that has a lot of miles and the usual wear. Being synthetic it probably does have enough protection since it's only that 5 weight when cold, but couldn't that create a lot of wear and oil consumption on cold startups??? Anyway I can't wait to hear from CAT about my oil but I'm beginning to think the USPS lost it which would suck.
