ok so this is like my thirs oil change since i got the bone... for some reason i got and put 10w40, not 10w30 in the car...crap! what effects can this have on the car.. i am really more concerned about any problems that might happen?? let me know
its a 98 ssei just so you all know....thanks in advance

If I recall correctly the compounds used to make the molecules change from 10 weight to 40 weight tend to cause deposites in the rings. That was why GM banned that weight long ago. Now???

I'd just bit the bullet change the oil with 10-30 take off the filter and drain it and reinstall it.

You should not have any problems with the 10w40 oil. I have the oil dealer changed at the Pontiac delaership only since they have a Quick Lube outlet; the oil weight they use is 10W40.

I tend to agree with ssei1995, 40 means it will stay thicker at higher temps. If your car has any problems with blow-by this might even help it a bit. If you ever used one of those "stop blue smoke" products you notice that it'* like putting honey in your motor, and the label says good for any vehicle. I might be wrong but I would just say go back to 10w30 at your next change.

No problem at all.
Don't worry about it.
It really means that when the oil is cold (rated at 0*C) it'* viscosity won't be thicker than 10 weight and when warm (rated at 100*C standard) it'* viscosity won't be thinner than 40 weight.
If you can get away with it you should use thinner oil...ideally 0 weight...to keep frictional losses to a minimum in order to maximize hp when starting in cooler weather.

The wider the viscosity range, the better quality oil....usually.

Racers will sometimes use 0W30.
If you drive in warmer temps you should use a straight weight oil like 30.

I use 5W50 in my 6.6L and 5W30 in my 3.8L
I use 75W140 for my rear drive differentials.

About a month ago, I was at the store doing my shopping, including getting some oil for my car. A man stopped me to talk about the oil that I had just purchased. As i turned out, he was a recently retired engineer from GM who worked with their various engines. He mentioned that the Valvoline 5w-30 turned out tops in the tests that they ran. He also said that none of the brands tested 10w-40 weight passed their tests. Unfortunately, as I was pressed for time, I didn't have the opportunity to ask him the 50 or so questions that I would have liked to have asked. I doubt that one use of the 10w-40 is going to cause any long term problems, but based on his advice, I would stay away from using it regularly.

Agreed with the above posts. You might lose 1 mpg but I would keep it in the crankcase until your next scheduled oil change. I go with 5W-30 Dino Oil during the winter months.

ok...i was worried there for a while.. but if you all think it should be more than good.. i will take your word(*) for it.... thank to all, and thanks it will not happen again