Don't forget your long term car maintenance costs like tyres, brake pads, wear and tear parts and servicing.

Your income is unpredictable as it depends on price of petrol, variable terms and conditions and luck.

If you are willing to work 12 hours and day, 6 days a week you may be able to make some decent income but after deducting your short term and long term costs I doubt it will be better than a regular 9-5 job.

Furthermore as a taxi driver you are not learning anything to further your personal development and future earning.

In short you should treat Grab/Uber as a sideline income instead of a full time job. It's hard work for low pay and there is not much future in it.