my sentra smokes after it warms up but still runs awsome what can it be?

Is it dark or light smoke? There are many reasons as to why your car could appear to smoke but to name a few: running too rich or lean, oil leak, or blown gasket somewhere. With that being said, look under your hood and check all around the block and oil filter for wet spots. Check to see if it's oil. Let me know what you find(if anything) so I can further help you. Good luck!

the color of the smoke would tell you what it could be. the fuel may be a little stale if white smoke, of the head/head gasket could be bad, but if the head, or head gasket was bad, then your car would not run for long. if it is black smoke, then you may be getting oil into your fuel, of getting oil into the fuel system. if antifreeze is entering your head, through the gasket, it will cause white smoke

it is white greyish smoke but only smokes when getting warm not when cold

it did have a little old gas that we added new gas and fuel addidtive to i beleive this may be the issue it only smokes whe warm and driven not idleing

hmmmm. well, from the sounds of it, you may be getting coolant into your fuel. the head or head gasket may be the cause, but could be other things also. i do not know for a fact that that is it without looking, but from what you are telling me, thats what it sounds like. how far do you drive it? and do you drive it that far everyday?

My Nissan sentra 2000.'engine was welapha overhauled..running well and fresh but after driving for while ...White smoke comes out from exhaust.