Son has a '10 Prius serviced at a local to him dealer. Happened to be at his house picking up granddaughter the other day and noticed spots of oil looking stuff where he parks his car. Didn't have a chance to mention it as he was already driving to my house. After TG dinner, I did mention it and we took a flashlight out and looked at the dipstick. Noting on the cloth using the lay it on a cloth and look for the contrast trick. So at first light I got a quart of oil and added it. Still nothing visible on the dipstick. Trip to my dealer, up on the lift and 10 minutes later the drain plug and its installation is determined to be the culprit. $6 part and a change of oil and no labor cost and we are good to go. Gosh only knows how long it would have been before the engine seized as he didn't even know how to open the hood. Moral of the story: the glance you give your parking space could save your engine.
