Skip's 4x4
Skip's 4x4
Diesel vs Petrol

by Mark Peacock

One of the many choices you have to make when buying a 4WDrive is whether to have a diesel or petrol engine. There is a lot of folklore and myth that a "real" 4WDrive HAS to be a diesel, but there are some good arguments for a petrol engine. Now, before any diehard 4WDriver complains that I must be biased if I even dare to consider a petrol 4WD, let it be known that I drive an 80 series 4.2 diesel cruiser.

Although many diehards may disagree, the main thing to remember is that both fuel types have advantages and disadvantages and there is no definitive answer on which is "the best". At the end of this article is a summary on the advantages and disadvantages, so if you want to cut through the "waffle" click here to go to the summary.

Perhaps the most common (and only partially correct) conception for the diesel is that they are slow compared to a petrol engine (note, I am always comparing similair capacity engines unless otherwise stated). But when you add   a turbo to a diesel, then the equation changes. A turbo diesel has the equivalent top end power of a petrol while still having the low down torque of a diesel and the same good fuel economy. While this may sound like the perfect solution, the problem is the extra cost. One of the advantages of the diesel is it's good fuel economy but the extra cost of the turbo would more than pay for the increased fuel cost.

A diesel engine is built stronger than a petrol as ......

A diesel will always have better engine braking due to its design.....

Paramater

Diesel Petrol
Purchase Price Typically $1,000 - $3,000 extra, and up to $10,000 extra for a large capacity turbo.  
Maintenance Requires more frequent oil changes, but otherwise significantly longer periods between major maintainence. Generally longer intervals between services (10,000 kms vs 5,000kms), but often more costly when they are due.
Engine life (between overhauls) 350,000 to 500,000 kms between rebuilds
(varies significantly with maintainance and use)
200,000 to 350,00 kms between rebuilds
(varies significantly with maintainance and use)
Fuel Economy Generally 10% to 35% better  
Power Only a turbo diesel engine comes close to a similair size petrol. Normally has a significantly lower redline. Typically 25% more for a similar size engine.
Torque Better at low revs and generally a "straight" torque curve. Can be peaky in small capacity turbo engines. Although most 4WD engines are designed for good low down torque, a diesel is still superior
Fuel volatility Volatile, but significantly less than petrol. Highly volatile, vapour will ignite up to 20m from a flame source
Engine braking Very good in manual, OK in auto. OK in manual, poor in auto.
Engine weight Typically 10 to 20% heavier for a similair capacity engine  
Exhaust Temperature approximately 600 degrees celsius approximately 800 degrees celsius
Water rating Excellent, provided water does not get into the air intake. Ignition prone to shorting when wet.
(c) 4WD Encounter 1998

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This page was last updated on 17 Oct 2003