Thursday February 11 2016

Ask the mechanic : Why does my x-trail consume a lot of fuel?

It is important that you replace car parts that

It is important that you replace car parts that are out of service to solve the problem of high fuel consumption. PHOTO BY MICHAEL KAKUMIRIZI 

By Paul Kaganzi

Hi Paul,
I recently imported a model 2001 Nissan X-Trail. It’s a petrol car with an automatic transmission from Japan and the milleage on the clock was 115,000km. The engine light is now on, it loses power on ascent and fuel consumption is high. What could be the problem? What is the fuel econony of a Nissan x-Trail.
Regards, Lawrence

Hello Lawrence, the check engine light on your dash board indicates that there is an emission fault. This can be caused by a couple of factors such as faulty sensors (oxygen sensor or air flow sensor) which regulate the delivery of fuel by the engine computer, worn out spark plugs or damaged ignition coils.
A computer diagnosis at a garage near you will quickly point out the trouble causer. A 2.4 litre petrol Nissan X-Trail will give you an average of 12.5 km/ litre on a combined run (highway and urban).
Word of caution for the X-Trail confirm that your fuel filter has been replaced at the 100,000 km service mark to avoid damaging the fuel pump.It is advisable to use fully synthetic engine oil for prompt lubrication at start up in order to avoid damaging the timing chain and plastic chain guides in the engine.
Discuss my suggestions with your mechanic.

Hi Paul,
Thanks for the good work. I have a Subaru Imprezza N10, 4WD, Non Turbo, Model 2004. It is a 1.5cc but consumes fuel much more than a Toyota Noah 2.0 4WD.
I have tried changing the spark plugs, but it has not helped. I have recently realised that the Thermostat is still fixed.
What do you think is the problem and what is your recommendation?

Hello Ronald, besides bad spark plugs, there are other factors that can cause poor fuel economy on your Subaru. A dust clogged air filter will restrict air intake which affects the volume of air delivered to the throttle.
This will impact on the air fuel ratio causing more fuel to be delivered than burnt in the combustion chamber.
Ask your mechanic to check if there is a faulty fuel injector which delivers more fuel than it should. Lastly, a computer diagnosis will be useful to determine whether you have faulty oxygen sensors.
These sensors monitor and relay information about oxygen levels in the exhaust to the engine computer (ECM).
This will help to determine the efficiency of engine combustion and regulate fuel delivery.
A faulty oxygen sensor will cause a spike in fuel consumption as the ECM guesses how much fuel to deliver.

Hi Paul,
Thank you for the advice that enlightens us about vehicle maintenance. I own a Toyota Land Cruiser Prado 1999 model with a petrol engine. I took it for servicing and the mechanic changed the engine oil and replaced it with 15w40 engine oil with the container labelled engine oil for diesel engines and when I asked the mechanic why he had done this, he said the oil is used for both engines. Is it true?

And if not, what is the effect on the engine and what can be done to correct an anomaly? What is the correct engine oil for servicing such cars and the best servicing stations? Does oil expire before it is used? I need your advice on this before the problem escalates. Thank you

Hello Twinomugisha,
Petrol and diesel engine oils have the same anatomy because they are formulated by blending base oils and additives to give them specific performance features. The difference between the diesel and petrol engine oils lies in the performance requirements of each engine type. The viscosity of diesel engine oil is different from that one of petrol engines. Viscosity is an oil’s resistance to flow and shear. As you increase the engine temperature, the oil viscosity lowers and it flows faster. The selected viscosity of engine oil allows it to be easily pumped up the engine at the lowest engine start up temperatures while providing protection to components and passing through the oil filter and draining back during normal running temperatures.

Diesel engine oil has a higher viscosity index compared to petrol engine oil. This means that if diesel engine oil is used in a petrol engine during cold starts, the oil may be too thick for the oil pump to deliver to vital components promptly.
This leads to premature component wear and tear. Engine oil viscosity rating can help you identify whether an engine oil is suitable for your engine type. The rating of engine oil viscosity produced by reputable manufacturers is done by the Society of Automotive Engineers, who issue an SAE rating after extensive laboratory testing. This is displayed on an engine oil can. For instance, the 15W40 you mentioned has the W which stands for winter. This means that this oil will meet the requirements of cold cranking and oil pumping at below minus 15 degrees centigrade up to 40 degrees summer temperature.

The detergent and anti-component wear additives load per volume of diesel engine oil is higher than that of petrol engine oil. This is because diesel engines produce more soot and combustion by products compared to petrol engines. These additives such as zinc dialkyldithiophosphate (ZDDP) can be destructive to petrol engine emission cleaning exhaust catalytic converters yet they are tolerated by the diesel emission cleaning diesel particulate filters (DPF).
You can also tell the correct engine oil for your car’s engine by reading the API (American Petroleum Institute guidelines). In the top section of the API is a service designation. This designation will either start with an “S” which stands for service or spark ignition for petrol engines or a “C” which means commercial or compression ignition for diesel engines. As an example on the attached picture of Shell Helix HX5 engine oil can, the API classification is SL/CF which means it is suitable for both petrol and diesel engines.

Ask the mechanic
By Paul Kaganzi
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