Almost every driver who installs LPG asks the same question sooner or later: why does the car use more litres on gas than on gasoline? The answer is straightforward and not a reason to worry, but there is a threshold above which higher consumption stops being normal and becomes a symptom of a real problem. This guide explains where that threshold is, what to look for if it is crossed, and how to measure LPG consumption fairly.
Why LPG Always Uses More Litres Than Gasoline
LPG has a lower energy content per litre than gasoline. One litre of LPG contains roughly 73-78% of the energy in one litre of gasoline. To produce the same power, the engine must burn more litres of gas. In practice, this means 10-20% higher consumption in litres, depending on the engine, the system and the driving conditions.
In concrete terms: if a car uses 8 litres of gasoline per 100 km, on LPG it will typically use 8.8-9.6 litres. The savings do not come from consuming fewer litres but from the price per litre. LPG is significantly cheaper than gasoline, so even with 15% more litres the monthly fuel bill drops. That is the entire point of an LPG installation: not lower litre consumption, but lower costs at the end of the month.
If the difference exceeds 20% under stable conditions (same routes, same temperature, same driving style), something in the system is not working properly and needs to be checked.
Map Calibration as the Most Common Cause of Excess Consumption
The LPG controller manages how much gas the injectors deliver based on electronic maps. Those maps are configured during installation and recalibrated at service intervals. If the maps are set to deliver too rich a mixture, the engine runs but wastes fuel.
The problem arises in two typical situations. First: something changes on the gasoline side (new spark plugs, intake manifold cleaned, MAF sensor replaced) and the LPG maps are not recalibrated. The old maps were tuned for the old engine state and no longer match. Second: the calibration was simply never repeated since installation, and parameters have drifted over time.
Map recalibration is a standard part of LPG system servicing and in many cases is enough on its own to bring consumption back within the expected range. That is why every major gasoline-side intervention should be followed by an LPG map check.
LPG Filters and the Reducer
The LPG system has filters for both the liquid and the vapour phase that catch impurities from the fuel. When these filters clog, gas flow drops and the mixture becomes unstable. The engine compensates in various ways, and the result is higher consumption, sometimes accompanied by mild hesitation or power loss. Filters are replaced every 10,000-15,000 km, but many drivers neglect them and run twice as long on the same set. A simple filter replacement often solves the problem entirely. More on intervals and what a routine system check includes can be found in the LPG service guide.
The reducer (evaporator) converts liquid LPG into vapour and regulates outlet pressure. When the membrane weakens or the spring loses tension, pressure fluctuates and the injectors do not receive a stable supply of gas. The effect is similar to clogged filters, but usually worsens under higher engine load or when the engine is cold (especially in winter). Reducer health is checked by measuring outlet pressure under load.
Spark Plugs and Coils, the Silent Culprits Behind LPG Consumption
This is the cause drivers rarely guess on their own, yet in practice it accounts for a large share of visits. LPG requires a stronger spark to ignite the mixture than gasoline does. When a spark plug is worn or a coil is weak, the spark may be strong enough for gasoline but not strong enough for gas. The result is incomplete combustion on LPG, which directly translates into higher consumption, while on gasoline the difference is barely noticeable.
Many drivers assume the problem is in the LPG system, when in fact replacing the spark plugs or checking the coils would fix things immediately. If you notice that LPG consumption has risen while gasoline consumption has stayed the same, spark plugs and coils are the first candidates to check. More on intervals and how to choose spark plugs is covered in the spark plug guide.
Driving Style and Leaks as Special Cases
Driving style affects LPG consumption just as much as gasoline consumption, but on LPG the difference is felt more keenly. High-rpm driving, sharp accelerations and frequent city stop-start increase consumption on both fuels, but on LPG this shows up as an extra litre or two per 100 km because the baseline consumption is already higher than on gasoline.
A gas leak on hoses, fittings or valves is a serious case that goes beyond consumption. Even a small leak reduces the amount of gas reaching the engine and raises consumption, but more importantly it is a safety risk. If you smell gas in the engine bay or near the tank, an inspection is urgent, not just because of consumption but because of safety. More on symptoms that point to LPG system issues can be found in the guide to poor LPG performance.
How to Measure LPG Consumption Fairly
To know whether your consumption is genuinely outside the normal range, you need a fair measurement. Fill the LPG tank completely, note the odometer reading and drive your normal route (a mix of city and open-road driving). When the tank is empty, fill it again to the top and note how many litres went in. Divide the litres used by the kilometres driven and multiply by 100. Repeat the same procedure on gasoline over the same or a similar route. A difference of up to 20% in favour of gasoline is expected.
Causes that are not specific to LPG, such as low tyre pressure, a stuck thermostat or worn brake mechanisms, raise consumption on both fuels equally. If you notice that gasoline consumption is also higher than usual, the cause is in the engine or the chassis, not in the LPG system. Those general causes are covered in detail in the guide to increased fuel consumption.
If you feel that your LPG consumption is too high and you are not sure whether it is normal or a fault, book an appointment and we will check the entire system, from maps and filters to injectors and the reducer.