Is it really important to fill up with premium fuels?

Our tech guru has the answer
Nov 22, 2011

Hi, Ferman!

I'm a regular reader of your column and I find your articles very informative.

I own a Toyota Innova and an Isuzu D-Max. The D-Max is a 2005 model and it's not CRDi. It also had the misfortune of suffering from a choking pump. Isuzu said this was caused by dirty fuel (I've been using regular diesel) and it had to be recalibrated.

Fuel companies tout their premium fuels to cleaner and to offer more power. Aside from the claimed better performance, do premium fuels really have other cost benefits like, perhaps, a longer engine or pump life?

I would appreciate your expert opinion on this matter as some people are not convinced of the benefits of premium fuels.

Thank you and more power.

Al

Hi, Al!

Thanks for being a loyal reader.

To understand the problems that you and many other diesel-engine-vehicle owners encounter, we need to take a quick look at how a diesel-fuel system works.

Like any internal-combustion engine, a diesel engine has a tank, a fuel filter, a fuel pump, and a fuel delivery and metering system. In a gasoline engine, the fuel delivery and metering system can be a carburetor or an injector. In diesel engines, it's the injection pump and injectors.

Fuel is stored in the tank, and it travels to the injection pump and injectors after it passes through the fuel filter. What's critical in prolonging the component life of your engine is the fuel filter. Its job is to catch and prevent contaminants from getting to either the injection pump or the injectors. The contaminants include water, microscopic particles and bacteria, which may clog the fuel system over time.

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When any of the components gets clogged, you get poor engine performance because there is no longer sufficient fuel getting to the engine.

On the other hand, when orifices inside the fuel metering system wear down, you are getting much more fuel than required. When that happens, you will see black smoke coming out of your tail pipe.

Either way, you need to get to a diesel center to check the condition of your vehicle's injection pump.

This is what happens during calibration: The line to every injector is checked for pressure and flow-rate capacity. They are calibrated to standard specification as required by the engine manufacturer. Anything that is out of spec is rebuilt, reconditioned, and parts are replaced when necessary.

Unfortunately, injectors are often neglected. Why do they need to be replaced? The answer is simple. They are part of the fuel delivery and metering system, and they are subject to a much harsher operating environment compared to the injection pump. If you are not going to check them for flow rate, volume and spray pattern, and if you don't rebuild them as necessary at the same time you have your injection pump calibrated, you're wasting resources and time, particularly when there's a drivability problem with the vehicle.

Recently, fuel companies have been coming out with diesel fuels claiming to offer better performance while being cleaner and less harmful to the environment. To my understanding, these products have been blended with additives that enhance certain properties of the fuel for the engines to run smoother and cleaner. Do note that if the mechanical aspects of the engine mentioned above aren't in proper working order, then fuel can only do so much.

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To minimize clogging and contamination I would use a very good fuel filter, choose where I get my fuel and change the fuel filter at a much shorter interval than required by the vehicle manufacturer. It's cheap insurance against a much more costly fuel system failure.

Hope this helps!

Regards,

Ferman Lao
Technical editor

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