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Wednesday, 4 January 2012

What’s the difference between petrol and diesel engine oil?

You’d better believe there’s a difference between petrol and diesel engine oils.

Surely oil is oil so what’s the difference between petrol and diesel engine oils, and why is this important? Can we interchange the two?

In the broadest sense, gasoline and diesel motor oils have the identical composition or makeup. They are developed from the blending together of base oils and additives to obtain a set of preferred
performance characteristics. Nevertheless, from this simple characterization, we start to diverge when evaluating the lubricant’s fundamental performance for each engine kind and in this post we’ll investigate the difference between petrol and diesel engine oils.

The important difference between petrol and diesel engine oils.

Viscosity
Viscosity is the single most crucial difference between petrol and diesel engine oils. Obtaining the right viscosity is of the greatest importance. The chosen viscosity needs to be pumpable at the lowest start-up temperature while still safeguarding the components at in-service temperatures.

When comparing the viscosity difference between petrol and diesel engine oils, by and large, diesel engine oil will have a higher viscosity. If we were to put this higher viscosity lubricant in a gasoline engine, several problems are likely to occur: The first is heat output from internal fluid friction. This heat influences the life of an oil. A good rule of thumb is that for every 10 degrees C you increase the temperature, you cut the life in half.


The second difficulty is the low-temperature pumpability of this higher viscosity. During cold starts, the oil may be very heavy and hard for the oil pump to supply to the crucial engine parts in the top end. This will undoubtedly lead to unwanted wear, as the components will be interacting without the advantage of lubrication.

Additives are a crucial difference between petrol and diesel engine oils.

Yet another difference between petrol and diesel engine oils is that diesel engine oil has more additives per volume. The most prevalent are overbase detergent additives. This additive has numerous roles, but the main ones are to neutralize acids and clean. Diesel engines generate a great deal more soot and combustion byproducts. Through blow-by, these find their way into the crankcase, forcing the oil to cope with them. If you had to put this extra additive load in a gasoline engine, the effects would be disastrous to performance. 

The detergent would perform as it is designed to and try to clean the cylinder walls. This could have an adverse impact on the seal between the rings and liner, resulting in lost compression and efficiency.

Emissions and the Catalytic Converter
A catalytic converter is a housing that contains porous metal filler positioned between the engine and muffler in the exhaust system. Its job is to transform toxic pollutants coming from the engine to stable byproducts before they enter the atmosphere. Some of the byproducts of combustion (lead, zinc and phosphorus) can severely cripple the converter’s ability to perform this job. Therein lies another significant difference between petrol and diesel engine oils.

 Diesel engine oils have a greater anti-wear (AW) load in the form of zinc dialkyldithiophosphate (ZDDP). The catalytic converters in diesel systems are designed to be able to cope with this difficulty, while the gasoline systems are not. This is one of the main reasons you don’t want to use a diesel engine oil in your gasoline engine.

If your car was built prior to 1975, there is a good chance it does not have a catalytic converter, and thus the difference between petrol and diesel engine oils on this point would not be relevant.

So how do you know if an oil has been developed for gasoline or diesel engines? When studying a label, look for the API (American Petroleum Institute) doughnut. In the top section of this doughnut will be a service designation. This designation will either start with an “S” (service or spark ignition) for gasoline engines or a “C” (commercial or compression ignition) for diesel engines.

Now you know a little more about the fundamental difference between petrol and diesel engine oils why not find out more about what synthetic oil change intervals should be? Add your email to our Habot Synthetic Lubricants RSS feed to obtain all the latest information about oils and synthetic lubricants.

6 comments:

Violet Jessy said...

Great comparison between petrol engines and diesel engines

Anonymous said...

this if the best technical comparison i have ever read written in laymans language and to the point.

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Petrol Engine said...

Very interesting post about diesel and petrol engines!

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