I had same problem. I thought im using wroing oil coz b4 this im using shell normal ones, the yellow bottle.
then i change to 15/50 coz I cant find any 10/40 at local shop. it still made white smoke and i had to top up around a litre each time I went to Kedah or go back to Terengganu.
Maybe because I always shift down the gear from gear 4 to 3 when entering downhill at Grik which made the rpms suddenly high and took all the engine's oil.
But after put 50/50 Toyota Coolant/Water it only consume less than before, the engines oil.
*High RPMs engine never should use ordinary engine oil,some says it slowly broke down the engine performance.