ASK THE MECHANIC: Is morning the best time to fuel a car?

Hello Paul, is petrol denser when it is cold and therefore do I get more petrol when I fuel in the morning? Jackson.

Hello Jackson, theoretically, petrol is denser when it is cold and it seems to make a solid case for the budget-conscious motorists to fuel their cars when it is cold as they hope to get more fuel than when the weather is warmer. However, this is a myth and the reality is that you may not experience any difference in your petrol miles or fuel quantities when you switch from fueling during the day to fueling in the morning when it is still cold.
Whereas the science that drives this theory is true, in reality most petrol stations keep their stocks of fuel in well-insulated underground tanks. The soil underground is cold and so the underground fuel tanks will keep the petrol or diesel cold at underground temperature until it passes through the pump nozzle.
This will be the case regardless of the warming up ground temperature.
The small amounts of fuel picking up ground temperature in the pump will be insignificant to the value of fuel you buy or the petrol miles you get out of it. The opportunity cost of going out of your way and the inconvenience of cuing up to fuel in the morning may not be worth your while in terms of fuel saving. Rather, fuel at any time of the day morning or evening according to your convenience.

My ABS fault light keeps flashing

Hello Paul, my Toyota Camry ABS fault light keeps flashing and when it does, the brake pedal makes a rumbling noise and shakes even when I brake slightly. Mechanics have failed to fix it. What can I do? Jacob.

Hello Jacob, your ABS (Anti-Lock Brake system) is faulty. You need to start with a computer diagnosis to identify whether it is an electrical or circuit problem with the wheel speed sensors, harness to the ABS controller or the ABS controller (ECU and Modulator). Occasionally the hydromechanical ABS modulator may fail and needs to be replaced.

The ABS system is designed to help a motorist avoid skidding and loss of control when braking on a wet surface. ABS works by applying the brakes in a pulsating motion to avoid wheel lock and skidding. The system relies on sensors at each wheel to monitor speed and the 4 channel electro hydraulic pump to deliver the brake fluid to each wheel. It is important not to ignore a faulty ABS system because it plays a crucial role as a safety feature during hard braking.

A faulty ABS system may cause poor brake performance or catastrophic brake failure because brake fluid is routed through the ABS modulator. Symptoms of a faulty ABS system include permanent display of the ABS warning lamp, an intermittent pulsating and rumbling motion when you apply brakes or intermittent loss of brake hydraulic pressure.

What is wrong with my Pajero?

My Mitsubishi Pajero 3.5 V6 GDI has started showing a check engine light. While it seems to be running well, I think the fuel economy is poorer and the engine seems to falter slightly when driving uphill. Might this be the beginning of many problems? James.

Hello James, the check engine light is switched on when the engine computer detects an emission (exhaust) system fault. If there is a fault in any of the areas or components which affect the engine performance or emission system, the engine will pick up this fault and display it when a qualified mechanic carries out a computer diagnosis. I suggest you find a garage equipped with this diagnostic tool.

My steering wheel becomes stiff

Hello Paul, I drive a BMW Mini Cooper with a failing power steering which makes it stiff. Could this be a service issue or do I need special steering fluid? Kezia.

Hello Kezia, the Mini Cooper has an electronic power steering pump which will sometimes fail at about 100,000 kilometres. BMW released a bulletin about this and covered the steering pump under an extended 10 year warranty for models built around 2006. This steering pump comes with an electric fan which sometimes fails due to circuit failure or mechanical breakdown.
This will lead to overheating and damage of the steering pump. Symptoms include intermittent power steering failure or difficulty steering. Before you attempt fluid service carry out an inspection to confirm that there are no fluid leakages on the steering system causing loss of steering ATF fluid.
This can cause poor steering performance. Carry out a computer diagnosis and inspection to rule out blown fuses or short circuits to the steering pump or fan. If found faulty you need to replace the pump and possibly fan.