Why Is My Car Using More Petrol Than Before?

Short answer: Start with the free checks: tyre pressure, air filter and how you drive. If those are fine, the usual causes in an older car are carbon deposits in the injectors and combustion chamber, worn spark plugs, extra engine friction from old oil, or an automatic gearbox that slips and wastes power.

First, measure it properly

Fill the tank to full, reset the trip meter, drive normally, then fill to full again. Divide the kilometres by the litres. Do this for two or three tanks before deciding anything, because traffic, aircon use and load make a big difference from week to week.

Free checks to do first

• Tyre pressure. Low pressure is one of the most common causes, and it costs nothing to fix.
• Air filter and spark plugs. A clogged filter or worn plugs make the engine work harder.
• Brakes dragging. A wheel that feels hot after a drive may have a sticking brake.
• Load and driving pattern. Extra weight, roof racks, more city driving or long idling all raise consumption.

Engine causes

• Carbon deposits in the injectors and combustion chamber, common with higher mileage and short trips. You may also feel hesitation or a rough idle. KM+ Nano Decarbonizer deep-cleans over one tank, or use KM+ Injector Cleaner for the fuel pump, injectors and intake valves.
• Engine friction from old oil. KM+ REVO Nano reduces friction and can be added to your oil at any time. At the next service, flush with KM+ Advanced Engine Flush and change to KM+ 900GT or KM+ 650GT.
• A dirty catalytic converter or oxygen sensor, often with a check-engine light or a failed emission test. A trained workshop can treat it with KM+ Nano Catalytic Cleaner.

Gearbox causes

If the engine revs rise but the car is slow to pick up, or the gearbox jerks or engages late when cold, the automatic gearbox may be slipping and wasting power. See KM+ AT Fix-IT for gearbox problems.

A simple plan for an older petrol car

1. Do the free checks above.
2. Clean: one bottle of KM+ Nano Decarbonizer or KM+ Injector Cleaner.
3. Keep clean: KM+ Advanced Fuel Additives at every refill. Reported results include a 2010 Perodua Myvi going from 320 km to 400 km per tank. Results vary by car and driving.
4. Reduce friction: KM+ REVO Nano now, or Nano Ester oil at your next service.

Common questions

Will a fuel additive alone fix high consumption?

Only if deposits are part of the cause. Tyre pressure, a clogged air filter or a slipping gearbox will still waste fuel, so check those too.

Should I see a workshop?

Yes if the check-engine light is flashing, the engine misfires or knocks, or consumption jumped suddenly. Those point to a fault an additive cannot fix.

Not sure which applies to your car?

Send KM+ your car make, model, year, mileage and what you notice. We will tell you honestly whether a KM+ product will help, or whether you need a workshop first.