Synthetic oil

[Intuit]

Many years ago I tried switching over to a synthetic blend.

Even though it was the same weight rating, the oil seemed much thinner in the engine.

I had more power because it was "lighter" oil, but the engine was noticeably louder and that made me uncomfortable with it.

So I got rid of it after about a week or two. Friction, makes an engine louder.

Currently have ~232k, no smoking or signs of impending failure; and drove with a cracked head for some time. In that time it has only been necessary to replace a few roller lifters.

For the Winters and Summers, the only oil I've ever used is Castrol 5w-30. I can tell the difference between different brands of oils just by running them through my fingers. Castrol is better. I don't like Penzoil and Valvoline. During the particularly hot months, I'll blend in between 25% and 50% 10w-30. Engine is a little quieter with the blend.

In short, let your ears tell the story. Louder during starts, go lighter. Louder during running, go thicker. Gets louder after some time, change the brand of oil that you use; it's failing. In the past I've heard it recommended that older cars continue using mineral-based oils as opposed to synthetic and synthetic blends. The reason for the thinner oil in newer cars is for the tighter tolerances (and cooler running temps) built into today's all alloy engines.