I suspect you're referring to oil that drips onto the road or parking lots. I doubt you're going to dump your drain oil in your neighbor's yard! The last thing I would want in my engine is something that is going to degrade into something else. We change oil because of the carbon that collects in it, and the additives that wear out in about 3,000 miles. Those additives are what differentiates good-quality oil from cheap stuff. (I run the cheapest stuff I can find in my '88 Grand Caravan, and it's been over 13 years since I changed it). Obviously I'm not suggesting anyone else do this, but it shows what oil is capable of. Even the cheapest farm and home store stuff is much better than anything we had 20 years ago.
Be aware too that you haven't heard of anyone living next to a highway, and their well is contaminated by engine oil. It actually evaporates. That's why you can smell hot or burned oil. It had to vaporize to get to your nose. I spilled a bunch of fuel oil in my basement years ago when switching the furnace. It only took about a week and a half before the smell was gone. If oil didn't evaporate, there would be a pile of puddles in Walmart's parking lot, and I could mop that up and wring the rag out over my engine! What you're seeing is the carbon and other dirt that doesn't evaporate.
Be aware too that very often an engine will develop a leak when switching to synthetic oil. I'm sure that doesn't happen to everyone, but I've seen it happen to enough of my students to be wary.
Saturday, July 25th, 2015 AT 7:59 PM