Car Parts and Accessories

With the petrol price of fuel ever increasing, it is wise to look for ways and means of cutting this cost to a minimum. There are three main factors involved when it comes to saving fuel:

• Vehicle efficiency;
• Driver ability;
• Vehicle use.

Auto Vehicle Fuel Efficiency

Telltale signs of fuel wastage include:

• a black exhaust pipe or black smoking from the exhaust when accelerating or starting;
• slow warm-ups;
• fluctuating temperature gauge;
• Easy cold starts and normal performance from a cold engine;

• hard starting with a hot engine, which tends to misfire while attempting to do so;
• clear spots on the garage floor under the engine, which could indicate the presence of petrol leaks.

Tests carried out by the AA Technical Department show that the biggest culprit is the carburettor. The best way to check this for yourself is to arrange for a gas analysis of your car, an inexpensive test which can be carried out by most garages or any AA Technical Department. If this indicates an air/fuel ratio of less than 13,8:1, or a carbon monoxide (CO) reading higher than one per cent, you are not obtaining optimum consumption when operating on the carburettor’s main jets. Depending on the engine speed and load at which the test was carried out, a rich air fuel ratio is likely to be caused by:

Main jets not correct for the altitude at which the vehicle operates.

• Float level too high.
• Power jets — where fitted — malfunctioning.
• An excessively rich automatic choke setting.
• Carburettor pump stroke set at uneconomical level.
• Incorrect idling adjustment.
• Blocked air filter (at a steady 2 000 r / min there should not be more than 0,2 difference in the air/ fuel ratio when the air cleaner is removed).
• Defective needle and seat.
• Check also that the:
• Compression pressures are normal.
• Cooling system thermostat and manifold heat riser valves are operating satisfactorily. The thermostat speeds engine warm-up from cold and helps to regulate operating temperature.

• Brakes do not bind.
• Clutch does not slip.

• exhaust pipes are not kinked or perhaps blocked.
• ignition system is set and operating properly.

• fuel joints, fuel lines and filter connections do not leak.
• fuel pump diaphragm does not leak (a small hole drilled in the lower housing of the pump allows fuel which leaks past the diaphragm to be noticed at an early stage. Should the hole become blocked, thinning of the engine oil will result).
• fuel tanks which have short filler pipes are not fitted with the correct petrol cap (spillage occurs on acceleration and/or cornering with a full or nearly full tank).

Remember too that:

• Radial-ply tyres offer less rolling resistance than cross-ply tyres and consequently give better fuel consumption (approximately 15 per cent).
• Under-inflated tyres use more fuel.
• A multigrade engine oil will reduce drag.

• Misaligned wheels (causing more friction) increase fuel consumption.
• Use of an air conditioner can increase fuel consumption by up to 50 per cent on small engines.
• It is a fallacy that the higher the octane number of the petrol used, the more power will be obtained from the engine. The only result is increased fuel cost. If unsure, abide by the manufacturer’s octane recommendation for your vehicle and do not try to economise by using a lower octane number than that recommended as this could cause damage to the engine, preceded by a ‘pinging’ noise.

Manufacturers recommend the maximum octane number for ‘wide open throttle’ driving: which most motorists use for less than 12.5 to 25 per cent of driving time. If motorists learn to drive more patiently and prudently, building up speed more slowly and not relying on `flooring’ the throttle, they may be able to use a fuel with a lower octane rating than that recommended.

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