Chevrolet Express

I have a 2004 Chevy Express Cargo Van
that has the 4.8 L engine, and is a HD rated 2500 version.

The vehicle is being used for construction use, and has about 65,000 miles. Lately its been about 90 degrees here in NYC, and I feel as if the engine is getting to hot, and the car is not driving quite the same. I know on 80's older cars usually at about 70,000 miles I used to go with a 10w-40, and things were fine. However I know engines have changed.

I was wondering, what type of oil should I use for summer, and should I use the 5w-30 in the winter?

Or should I keep the oil the same throughout the year?

Currently I am using a 5w-30 Castrol Startup oil
July 10, 2007.

My opinion/experiences I'll stay in one grade oil 10W30 or 40 thru out the seasons. When that battery/starter kick that engine over and fires up am gone-Hello coyote bar. Lol

Unless you stay in the Artic when you need to heat the oil thru the dipstick so it won't thicken up on you.

I use Pennz oil that's my best of all-yellow bottle!

For preventive maintenance change it every 2500 miles its good for the internals oh! Don't forget the filter that needs changing too.

Good Luck

Aug 26, 2007.