Low tyre pressure has a good suspension feeling as it suppresses defects and body rattle, while high tyre pressure gives a false impression of better engine performance. At times, engine oil is mixed with thicker oils to give a smoother feeling to the engine. Only an accomplished mechanic can detect this. Mark the following- 1. When the engine warms up, check the exhaust, preferably while driving behind the car.
Blue smoke indicates a weak engine while black indicates excessive unburnt fuel.
Ideally, there should be no smoke. Ask for the Pollution under Control Certificate. Stop the car and open the bonnet. Remove the oil filler cap with the engine at idling speed. The presence of smoke is an indication of serious trouble.