2001 Civic LX - Supposed to use 5W-20 (I think that's what it says on
the cap). I used 10W-40. It's what a mechanic recommended.

Not the 1st time I've used a diff oil than spec. Just wondering if
there can be bad consequences if I use the wrong motor oil?

Also, what exactly do those numbers and letters stand for? I think it
refers to viscosity but I don't remember which number?

Steven