Years back when I thought I was an oil expert, I convinced my buddy to use 20W50 in his car, a Firebird of unknown year and engine. I specified in no uncertain terms that this should be done in summer only. No starting below 50 F. (At that time I thought "Shell Super Plus Artic 0W30" was best for Canadian winters) I cannot recall if it was dead dinosaur or synthetic. Anyway, he took his car into a shop and when he came back they had an engine (he cannot be 100% sure it was his engine) dismantled on a bench, they said it was toast and the likely culprit was 20W50. He was never asked to sign a thingie saying they could do whatever they want, and that got him out of his pickle, but I still think about it some times, and since I have you all to chime in on how wrong I was, I thought I'd ask. On a related note, I used 20W50 in lawn mowers for years. I consider it totally bad to start a mower at under 50 F, and I usually allow them to warm up, anyway. The young man at the mower shop once said that 20W50 was "abusive" and to always, always, use straight 30. Our latest mower says that on the oil cap and on the side of the engine, so fine, but the previous one was a used B&S with 6:1 comp ratio, air cooled. I KNOW you have seen them around. Why would 20W50 be bad? I have a B&S repair manual with a viscocity vs temp guide that shows 20W50 would be the stuff to use! I will try my best to not be too defensive to those that tell me I was wrong, especially on the car.