Quoted From Third Gear:
Well, hopefully nothing is damaged, but those places aren’t known for using the best oil. One guy told me they just dump 30wt oil in whatever comes in – they don’t care what it uses. I thought he meant 5w30, but he said, “no, striaght 30wt!” my eyes got as big as golf balls.
I would use what the manual recommends. A 5w20 won’t hurt anything though. The 0w20 is just a little better flowing when the engine is cold – which might be beneficial to you in the winter time. I’m sure anything you get will be better than what they were using.
I don’t know how some of these places stay in business. A coworker of mine had his oil changed on a new Jeep and they didn’t tighten the oil filter properly (or used a defective one). He got about 2 blocks away and oil was everywhere. Don’t even get me started on them stripping the oil drain plugs. I wonder if they charge extra to replace the one they strip? Must be.