Can a car engine begin to burn oil with no noticeable performance or fuel consumption difference / or noticeable white smoke out from the exhaust?
Assuming it loses about 800-900 ml per 1000 km.
I am noticing small drops of oil under engine after parking but I want to make sure where to solve the problem.
First, get the oil leak fixed. You really can't just how much oil the engine is consuming while there is a leak. You could be leaking a lot more than a few drips while the car is moving and not know it.
To answer your question... It depends. If you're burning a small amount of oil, you won't see smoke and might not smell anything. As the amount you burn increases, you will start to smell it and then start to visibly see smoke in the exhaust.
As far as performance goes (and we assume you are burning oil)... Oil is getting into the cylinders and burning so we know that your compression is probably not as good as it could be. You're not going to get complete combustion because of the contamination, and both of those will take away power. Again, maybe its a very small amount that you won't detect in the real world - depends on severity. Long term oil burning could also lead to an exhaust system restriction (assuming catalytic converters) which would reduce power.
Fuel consumption I'm not sure on. With a car that has electronic fuel injection, it makes sense to me that burning oil is going to mess up oxygen sensor readings which is going to lead to less-than-optimal fuel regulation. Because of that I'd assume gas milage will suffer.
You didn't mention it, but some of these problems are going to be accompanied by a check engine light involving the exhaust.
