Bests & Worsts Reviews from Amazon

Once upon a time, my car (which I inherited at 120,000 miles) had a significant amount of piston slap during a cold start. After it warmed up, it would go away. I figured it would be an interesting experiment to switch to synthetic oil to see what the hype was about and if it really made a difference in engine longevity, especially now that my engine was "getting on in its days". I got some of this Castrol 5w30 full synthetic purely because BMW and Triumph motorcycles use it as their factory fill. Maybe Castrol pays them to be the factory fill, but hey, if the engineers are happy with it, I'm sure it'll be okay. After the first cold start, I immediately noticed that the piston slap would go away by the end of the driveway, rather than most of the way to my destination. I figured that was a good thing. Oil is slipperier when cold, does a better job lubricating when cold, engine has less wear on cold starts. Brilliant. One day, my friend told me that "all synthetics are the same" so long as they pass the same API certifications, etc. and you should just buy the cheapest one at the time. I found some oil from a company that starts with "valv" and ends with an "e", and it was the cheapest, so I got that. Piston slap came back. Mind you, it wasn't as bad as when I was using dinosaur oil, but it was definitely worse again. After a very short 3,000 miles, I switched back to this Castrol synthetic, and the engine doesn't slap at all when cold, the valves are quieter, it's just generally happy! This Castrol oil seems to like to "stick" to surfaces in the engine, so that even after a weekend sitting in the driveway, come a cold Monday morning, the oil will still be on the metal surfaces to lubricate it even during initial startup. I'll definitely be buying Castrol for a very long time.