Two stupid oil questions

[grandkodiak]

I know that the lower the number the more fluid the oil, but what is perfered during hot weather? Like in the summer, would one pick 5w or 10w -30? The hot weather will make all the oils run more fluid, but do you counter act that with thicker oil or do you want to enhance it by using an already runnier oil?

and, can you mix oil of different rates or will that cause problems? reason i ask there is because i dont remember what oil i had in there the last time it was changed, and i got a low oil warning, but cant figure out which of the two to put in?

[GP99GT]

usually its 5w30 for below freezing temps, and 10w30 for above

[grandkodiak]

so if there is 5w30 in there now, is it ok to add 2 quarts of 10w30? there is probably only 1-2 quarts in the actual motor, but i'm guessing it was 5w thats in there for some reason.

[BonzoHansen]

Yes, it is fine.

[bubba428]

taken from How stuff works....Should help you out a bit
mixing oils is never good...but it doesn't hurt as long as its a small amount


Multi-weight oils (such as 10W-30) are a new invention made possible by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature. This page from the Sci.Electronics.Repair FAQ offers the following very interesting description of how the polymers work:

At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-vis oils is to think of a 20W-50 as a 20 weight oil that will not thin more than a 50 weight would when hot.

[grandkodiak]

yea read that