What weight oil to use in the summer in a 2003 pontiac grand am

yes and no your are on border line see link below
http://tire-size-conversion.com/tire-size-calculator/
hope it helps

Here's a link to your oil change. Specifications Engine Oil Type Weight Capacity AutoZone com

Most likely 5W-30. The W is for winter. The numbers tell summer and winter. A quart of this oil will act like 5 weight (very thin) in the winter and 30 weight in the summer (thicker). Let's not go in to how that is done.
If you live up north, a 5W-20 would do well also. Down south 10W-30 is often used.

you can use 10w30 motor oil without any problem.

Does it knock hard or just rattle loud,? A lot of cars are noisy till the oil gets pumped up top. I hate to see people floor when they first start up, very bad idea, no oil up top, anyway, your oil weight goes by the outside temperature. If you live in Florida, it gets hot, I use 10w-40 year round, up north is a different story, 5w-30 in the winter would be fine, but summer time you could go heavier no problem. My brother uses straight 30 weight with a bottle of Marvel mystery oil as the 5th qt. The stuff works great. It cleans the inside of your engine like you wouldn't believe. He is one of these guys that takes the oil filters apart to check them out. Hope this helps.

use a 5/30 synthetic oil..its good for winter and summer.

5w 30 or 10w 30 during the winter. After an oil change... check your oil after 200-300 miles of use. Is the level the same? If so your weight is fine. If it drops, it's to light of an oil and your engine is now "drinking it" like fuel, move to a heavier weight. As far as Changing between winter and summer. Changing Oil weights is not bad for your motor so if the winter you go with 5w 30 and it works, great, shoot for the same during the summer. If it seems to "drink it" during the summer using this weight, go up to the next (10w 30)

That being said. Changing from natural oil, to synthetic, back to naturual , or vice versa... swapping back and forth between these KINDS of oil has been known to cause damage. so whatever weight you decide on, stick with one "type", natural or synthetic.

Check you owners manual.
But should be a 5-30 weight.

Talk to your local tire store an dsee what they recommend. I'm sure they will know what to do.

i use valvoline brand.