I use a Toyota sienna 1998 model using 1MZ FE Engine. I have used this vehicle for about 3 years. Any time I do an Oil change, within 2 weeks the oil level would drop to half the level. And there is no leakage anywhere on the engine. Usually every 2 weeks I top up the engine oil with 1 litre of Oil and in another two weeks I do same.

I have talked with my mechanic, he advised that I change the engine outrightly. However the vehicle still accelerates very well and it is not smoking. Every other unit viz AC, Radiator and others works perfectly well.

What should I do?

Ur piston rings are definitely tired. I suggest a change. Ur engine might not smoke cos d rate at which its burning oil is minute.