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Information > W124 information & history > Petrol vs Diesel vs LPG
Petrol vs Diesel vs LPG vs Alternative Fuels
The vast majority of UK cars are petrol-engined but the comparatively rare diesel-engined cars have a very strong following. As a result diesels attract a premium which often makes them less attractive financially than a petrol car - particularly when annual mileages are not significant. The premium paid for an LPG or diesel car may make no sense if your annual mileage is low - and petrol cars are much, much easier to find... Alternative fuels are becoming more mainstream now and offer an environmentally-friendly way of powering diesel cars

Average fuel consumption
There are lies, damned lies and then there are fuel consumption figures. Below are average figures based on a normal mix of town / open road use, plus the maximum figure you might achieve when crusing at around 70 mph. These figures are based on our experience and reports from owners

Fuel consumption for the six-cylinder petrol cars is directly related to your right foot - used with care they will exceed 30 mpg easily on a run

E300 Diesel  3336

Petrol-engined cars offers a number of benefits - they're easy to find, competitively priced and acceptably economical as well as being good to drive. The range of engines is large (see our Model Range page for details) with capacities from 2.0 to 3.2-litre. The 2.0-litre four-cylinder engine is surprisingly willing and not as underpowered as it might first seem.

The four-cylinder 2.3 and later 2.2-litre multivalve engines offer a very acceptable balance of economy and acceleration and lack only the torque and refinement of the six-cylinder cars. We recommend the four-cylinder cars for economy, general town, country and touring use, but not for towing or heavy loads

The original six-cylinder 3.0-litre engine came in 12 and later 24-valve versions; both are effortless, smooth, punchy engines but the 24-valve engine gives more bite while staying acceptably economical. The 2.8 and 3.2-litre six-cylinder multivalve engines were introduced, along with the 2.2-litre four, to replace the older 2.3 and 3.0-litre engines. The sixes are markedly punchier and smoother than the fours and we recommend them for long-distance, high-speed cruising, for towing and for carrying heavy loads

The longevity of Mercedes diesel engines is legendary and well-deserved. Heavy, low-revving and simple, these engines will run forever if scrupulously maintained. Mileages of 200k are commonplace and 500k-plus not remarkable

The original diesel models, the 250 and 300, have non-turbocharged diesel engines of 2.5-litre (five-cylinder) and 3.0-litre (six-cylinder) capacity. The 2.5-litre produces 93 BHP and 117 ft/lbs of torque and the 3.0-litre, 111 BHP and 140 lb/ft. These cars are slow to accelerate but, once up to speed, will cruise all day at a useful pace. There is surprisingly little difference between the early 250 and 300 diesel engines in terms of economy and acceleration and both are smooth and quiet - and capable of cruising at 80+ mph all day whilst delivering 33 mpg average

The late-model multivalve diesel was a short-lived model that appeared for a couple of years before the turbodiesel 3.0-litre was launched in the W210 (see model range). The 3.0-litre six-cylinder multivalve "606" diesel engine produces 134 BHP and 155 lb/ft torque but still delivers 30-32 mpg average. Compared with earlier diesels the multivalve offers a big improvement in terms of driveability. As a result multivalve diesels are very sought-after and command a significant price premium

Mercedes diesels are undeniably relaxing to drive - but that's partly due to their lethargic acceleration. Drivers used to modern turbodiesels may struggle to come to terms with an early W124 diesel but for long-distance work they are superb. A multivalve diesel is as quick as an E220 but the engine is smoother and as good as - if not better than - a Mercedes petrol engine

All diesel W124s are great long-distance cruisers with a huge range - just over 500 miles on a tank is possible - but the multivalves offer a blend of torque, performance and economy that is difficult to beat

There are no "official" LPG cars from Mercedes-Benz UK but cars have been converted using a variety of systems. Conversions differ wildly in price, quality and sophistication, making an informed choice difficult. Great care should be exercised when buying an LPG car and considerable thought given to the economics of a conversion

Some conversions install the LPG tank behind the rear seat thereby blocking access to the additional seats (if fitted) and destroying the carrying capacity of the car. Other installations mount a small toroidal tank in place of the spare wheel. These installations give a very modest range of around 160 miles - ideal for town use or to extend cruising range - but they do require tyre sealant to be carried or the spare wheel to be relocated (and bolted down) in the load area

Unfortunately the W124 estate doesn't lend itself easily to LPG conversions. The shape of the spare wheel well and the requirement to keep the loadspace clear mean that neither conversion is ideal. By contrast W124 saloons and coupes are ideal candidates for spare-wheel tanks as the spare wheel sits flat under the floor, not one side like the estates

If you're convinced of the need for LPG we suggest finding an installer who has experience of thse cars. Some installers mount the filler on the nearside for easy access to a spare wheel well tank but an LPG filler mounted behind the fuel flap is much neater

Alternative fuels
There is increasing interest in running cars on alternative fuels, either to reduce greenhouse gas emissions, to reduce our dependence on oil, to save money or all three

The CO2 produced when burning biofuels does not add to the net amount of carbon dioxide in the atmosphere as the carbon in the fuels was extracted from the air by the plants that were use to produce the fuel. Rapeseed oil, palm oil, sugar cane and wood pulp are common sources of alternative fuels. The oils go to make up a vegetable oil alternative to diesel, and sugarcane (Brazil) and wood pulp (Europe) are processed to produce Ethanol. Ethanol-powered cars are available in the US (4.5 million cars can use up to 85% Ethanol, Ethanol-only cars are rarer) and Sweden (SAAB 9-5 Ethanol and others). Many US petrol brands are blended with Ethanol

The only W124s that offer the possibility of using alternative fuels are the diesels. The punitive UK tax regime makes it almost impossible to make savings when using alternative fuels but that hasn't stopped people from experimenting and converting cars

The simplest alternative fuel conversion involves pouring cooking oil into the fuel tank (of a diesel car) and turning the key. The Mercedes non-turbocharged diesels respond well to this approach but it's not recommended for long-term use as cooking oils are thicker than diesel, and so more likely to cause fuel problems in cold weather, and more corrosive

More complex conversions include bigger injectors with a different spray pattern, heated fuel feeds and additional filtration. Some use a twin-tank system where the engine starts on diesel and switches to alternative fuel when warm. Others rely on manually varying the diesel/vegetable oil blend to run in all weathers

Running with SVO (Straight Vegetable Oil), rapeseed oil, filtered (used) cooking oil or new cooking oil is not as straightforward as it may seem. We advise prospective users to research the topic thoroughly

In a surprise move in 2007 Customs & Excise removed the requirement to account to them for duty on vegetable oil, and other alternative fuels, if you consume less than 2,500 litres a year. On an E300 Diesel that equates to about 17,000 miles making alternative fuels a viable and legal alternative