In the wake of our recent six-vehicle comparison test in outback South Australia during which the HiLux Rugged X test vehicle dropped into limp home mode four times, Toyota Australia has admitted a design flaw with the air inlet system of the 2.8-litre turbo-diesel engine and that a fix has been requested from Japan. And yep, the same 2.8-litre 1GD-FTV engine fitted to the Fortuner and Prado has the same problem too!
The design flaw allows dust to leak past the air filter and corrupt the readings of the mass air flow sensor, which measures the rate of air entering the engine. The engine control unit (ECU) uses the reading to determine the correct fuel ratio.
The corrupted data prompts the engine to go into limp home mode, a potentially dangerous outcome in the wrong situation, such as when overtaking.
We are concerned that the next stop for this dust is the turbocharger, head, valves and combustion chamber, but Toyota doesn’t share the same worries.
A spokesperson told us:
“The dust that makes its way through the filter is very fine and typically less than five microns in size. What can occur is that these very fine particles attach themselves to the sensor electrostatically. It is not an issue of the dust finding their way into any internal components of the MAF sensor.”
The Toyota spokesperson continues, “The dust particle size that passes through the air intake system can become statically charged and adhere to the MAF sensor. The size of these particles is around two microns. In general, this type of very fine dust is not known to cause engine damage.”
We weren’t so sure about what Toyota said, so we reached out to an expert: Ben Mullins from Curtin University. Ben is an associate professor with special interest in testing and researching automotive filtration systems. Fuel, air, oil, gases, and anything in between; the man knows filters. We asked Ben to pass his eye over Toyota’s statements, and see if they held up with him. Here is what he said:
“I am surprised by the comments from Toyota. Firstly, five microns is regarded as a ‘coarse’ particle in the air pollution world. It has been shown that fine particles (e.g. diesel soot) can cause engine wear. Soot particles are <300nm (0.3 microns) in size – albeit at high quantities in the oil.”
In other words, if those dust particles are making their way into turbochargers and internal engine components, they will definitely be contributing to an engine wearing out faster. Ben continues:
“Also, whomever made the comments about more frequent filter replacement/checks or compressed air cleaning is misguided. The issue here is probably the filter sealing rather than the filter itself, so disturbing the filter more frequently would likely make things worse. Proper tests would need to be done to see if the problem is the filter or the sealing, however flat panel filters can be difficult to seal, which is why heavy-duty engines generally don’t use them except for cabin air.”
In other words, constantly changing the filter isn’t going to help if the filter system is ineffective. There is a chance that the filter housing isn’t sealing correctly, so dusty air is bypassing the filter.
“Another common misconception is that changing your air filter more frequently is better for your engine. Air filters are not sieves, so capture the least amount of particles when new, and get better when they load with dust. So if the filter is the problem, changing it more often will let more dust through! Heavy vehicle manufacturers and filter manufacturers recommend changing filter based on pressure drop as this ensures both the longest filter lifespan and the least dust in your engine,” Ben says.
In other words, thinking of your filter like a sieve or colander is too simplistic – filters have more complex capture efficiency rates for particular sized particles, which often improves as the filter loads up with dust. So, a lightly used air filter will catch more dust than a brand-spanker. Once the filter gets overloaded and you experience pressure-drop (the filter is blocking the correct amount of airflow), then it’s time to change your filter. Black smoke under load is often a good indicator of this.
In the end, we think the takeaway from this is that Toyota’s problem with dust sealing and filtering is more serious than they are letting on. How much of a problem it is depends on how dusty your driving is, and how many kilometres you want to get out of your motor. If you’re driving really dusty roads regularly and want maximum lifetime out of your engine, you might want to look at a replacement filter setup with better specifications.