In article <1151097772.803097.296190@u72g2000cwu.googlegroups .com>,
stevenqrdh@gmail.com wrote:

> 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

The first number is the cold viscosity (compared to cold oil) and the
second is the hot viscosity (compared to hot oil). The wider the range,
the more stable the viscosity is. The wide range is often accomplished
by adding polymers that reduce other qualities of the oil. Sometimes
synthetic oil is stable on its own.

The problem with using too thick of an oil is that it pries apart moving
parts, flows slower, and generates more friction heat. 10W-30 is
probably fine in hot climates but I'd drain the 10W-40.