Normally, the smoke coming out of the exhaust is colorless, or sometimes a little bit whiteish but quickly fade afterward. If you see the smoke coming out in blue, your car might have one or more oil-related issues. Now look at the smoke more closely and see if:
1. The smoke comes during start-up and fades away within seconds
The problem might be the valve guides or valve seals. When the car is idling or has not been operating for a while, the oil can slowly leak through a worn-out valve and accumulate at the rear of the valve. The leaking oil will then be burnt when your car is started and turn into the blue smoke that you see.
2. The smoke comes during deceleration
One more situation when a blue smoke stripe could be the result of a damaged valve is at the deceleration time. That's when a volume of vacuum gets guilt up inside the track and could suck some oil through the valve if it's too old.
Oil can leak through an old valve and get burnt in the way through the exhaust pipe
3. The smoke comes during acceleration
On the other hand, if the smoke appears when you're accelerating, the problem might be in the oil control ring. When this part (or the cylinder even in some rare occasion) is damaged, oil can slip through the ring when the piston moves back on forth inside the cylinder. In general, the control ring will come in full contact with the oil, echoing it back to the crankcase.
One common mistake is when the smoke occurs, more often than not, people find a broken PCV valve (positive crankcase ventilation) and immediately attribute the problem to it. Actually, while a damaged PCV can cause a huge loss of oil and failure in the gasket and seals, but it's not the main result of why the oil smoke happens (you still need a new PCV valve though)
A Blue Smoke Problem | Wheeler Dealers
4. The smoke only goes away after oil changes and gradually comes back afterward
Another subtle phenomenon of blue smoke is that it disappears when you change the oil and all of the above components, but out of nowhere it happened again. This might due to a fuel leak in the system. If you want to be certain, pull the dipstick out and smell the fume. If you detect the fuel smell, a leak in the system is possible. There are many reasons such as a stuck fuel injector, defects in the pressure valve that let the fuel to leak into the oil tank.
You can smell the dipstick to see if there's a fuel leak