When was the last time you checked your air filter?
The air filter in your 4WD does a very, very important role. If you were to remove it and drive on any dusty roads, your motor would live a substantially shortened life.
Given replacing and repairing 4WD motors is not cheap business, its worth taking the time to understand and look after your air filter.
What does an air filter do?
The air filter in your 4WD takes air from outside, removes any particles and sends the cleaned air into your motor. This is used in the combustion process, and a lot of air is required.
What happens if dust gets through or around an air filter?
If your air filter happens to leak dust or somehow dust gets around it, or enters after the filter, the particles enter your motor and cause wear to occur at an extremely high rate. If you are running a turbo, it will attack the turbo ‘blades’ first, and start to wear them out.
If you don’t have a turbo, it enters inside the motor, and starts to wear out internal components. In a way, its much like rubbing sand paper up and down pieces of your engine.
If your 4WD doesn’t leave the city, your worries are reduced dramatically. The air around town is substantially cleaner than when 4WDing, and your mechanic will clean or replace the air filter as required.
That said, dust is everywhere; building sites, empty blocks, pollen and general rubbish, and your filter is still very important even if you only drive on bitumen roads.
In the bush
Its out in the bush where your air filter does the most work. Gravel roads, bull dust and even in sand the air sucked in by your 4WD contains huge amounts of nasty particles just waiting to damage your motor.
If you are doing a lot of work off the bitumen, your air filter will not last the service interval given by your manufacturer.
This means it becomes full of gunk, and will eventually get damaged, or cause your engine to run poorly. Excess fuel consumption and a lack of power are both results of air filters that are not able to breath properly.
Its good practice to remove the air filter on a regular basis, and clean it or replace it if required. Follow the instructions on the filter if possible, or that of your vehicles manufacturer.
Some filters are washable (but must be completely dry before you put them back in), some are OK to bang against a tyre to knock the dust out and others must be blown out with compressed air.
If you are going to blow them out with compressed air, you should always, and only, blow the dust from the opposite side that the air goes through, so you aren’t forcing any particles into and potentially through the air filter.
Is your air filter sealing properly?
I’m sad to say this, but there are some vehicles out there that have poor sealing air boxes. I have heard this from several 200 series Land cruiser owners (and the 70 series too!), and other makes. Essentially, after some dusty driving, you can see dust on the clean side of the air box.
Pay attention to this, and if you see any dust at all getting past the air filter, jump up and down at the manufacturers nearest location; its just not good enough. No amount of visible dust is acceptable when it comes to your air filter, despite what they might tell you.
Unfortunately, often the dust isn’t getting through your filter, but around it. In many cases, the filter lip doesn’t get pressed down with enough force from the air box, and dust just bypasses the filter all together. It’s been suggested by a number of people that the use of a good rubber grease around the rubber part of the box or air filter will increase your air boxes sealing arrangement significantly.
It’s also very easy to install air filters incorrectly, and if you twist or damage the seal on the air filter when closing the box, you can be up for some extremely expensive repairs.
Air boxes can wear out
If you’ve had a plastic air box for some time, there’s a chance that its not doing its job properly anymore. The clamps lose their ability to apply proper tension, plastic expands and contracts (and can crack) as the motor warms up and cools down and ultimately they become the problem, and not the air filter.
I personally know of a 79 series owner who ruined a nice new engine because they re-used an old air box that wasn’t sealing properly!
It pays to have a good look at your air filter box, and ensure that things are working as they should be.
Cracked or damaged hoses
One of the worst things that can happen off road is you get a split hose. If this is on the suction side, you can be in a world of pain; dust and grit will get sucked in after the air filter, and your motor has no protection.
Take the time to check your hoses for damage, and replace them if its suspect. This should be done regularly on your trips, but also as a pre trip inspection.
Consider fitting a snorkel
Contrary to popular belief, a snorkel is not only fitted to 4WD’s for water crossings. You see, just a teaspoon of water going into your 4WD’s motor can destroy it, so it makes sense to raise the air intake and thus reduce the chance of any water going in. This is just one way to avoid drowning your 4WD.
However, one of the major benefits of installing a snorkel is that your raised intake sits above where a lot of the dust hangs while driving.
Instead of sucking air from just under bonnet height, which is often where you’ll find dust on a gravel road, you are sucking it from near roof height, where the air is much cleaner. This preserves your air filter for longer, and reduces the chance of dust getting into your motor.
You can buy a number of socks that fit over your snorkel, or just inside it, and are quick and easy to install and remove. These are often run on very dusty roads, and removed at the end of each day and cleaned or replaced.
A lot of them are mildly oiled, so the dust sticks to them. Anything you can do to stop dust getting to your air filter in the first place is a good idea, just watch the oil mist and suction; you don’t want to cause any restrictions.
Some vehicles come with pre cleaners installed prior to the air filter. These use a cyclone arrangement, where the air is spun around in a circle before going into the motor, and any dust is trapped. A lot of people swear by these, and they will make your air filter last a lot longer.
Aftermarket air boxes
Along with stainless steel snorkels, the newest fad is to ditch the factory air box and put something shiny in with a clear top. Whilst there are some legitimate reasons for doing this, you need to be 100% certain that the filtration is not being affected, both in the quantity of dust being let through, and the particle sizes. There’s no point having a nice looking air filter if its going to dust your engine.
Don’t use cheap air filters
One of the dumbest things you can do to a 4WD being used off the bitumen is to fit a different air filter to it. Filters that are fantastic for good air flow are often absolutely terrible for filtration.
You will end up with dust in your motor, and it will cost you a fortune. The best filter is either OEM, or a quality replacement one that exceeds OEM specifications. Don’t try and save a few bucks on an air filter, as a poor quality one will cost you heaps more in the long run.
I see people all the time trying to swap air filters so they can get more air flow, but if it comes at a loss of filtration, then you are making a very, very bad decision.
The stupid thing is that most air boxes will handle much more flow than what you need (unless you have done some pretty serious engine modifications) and fitting an air filter that would allow more air flow is completely pointless anyway.
Inspect your air filter and box regularly
There are lots of ways you can get dust into your motor. At the end of the day, it comes down to regular checks. Every time you open your air box, make sure you wipe a finger around the clean side of the filter. If you can see dust there, you’ve got a problem.
If in convoy, leave a big gap
On dusty, gravel roads, the quickest way to fill your air filter up with muck is to sit close behind another vehicle. You should not be driving in their dust cloud, and sometimes that means sitting a kilometre or more back.
Not only is this safer, but your motor will thank you too!
Carry MAF cleaner on modern cars
After the air box on most modern vehicles lies a MAF sensor, or Mass Airflow Sensor. This is linked to the vehicles computer, and reads the air flow to the motor. Over time, these can become faulty, and will not read correctly. This is especially the case if it gets dust on it.
A lot of modern vehicles do very well with having their MAF sensor cleaned periodically. You can buy a spray from your normal auto shops, unscrew it and spray it, wait for it to dry and put it back in and you are good to go. A MAF sensor that reads poorly will make your motor run inefficiently.
What filter do you run? Have you noticed any dust getting past?
Yep. Fine outback dust gets past the element gasket on my MUX. Doesn’t seal properly.
Unifilter replacement is the solution.
I think I’ve read one of your posts on this some time ago. I’ve had no issues with anything getting past my Dmax, but it is a worry. Is the unifilter finer?
No, the panel element gasket is thicker so there’s no blow-by.
Centre dust gets down to 5 microns.
It’s wise to use rubber grease as well.
Thanks for clarifying that. I might take a look next time I’m up for a new filter.
I purchased a k&m filter but decided not to use it after finding out it’s low filtration levels so I use the paper oem filter off-road and when off-road in heavy dust I use a unifilter sock with the K&M air filter. I figure this gives me a better chance to trap fine dust twice and a better air flow then a sock and paper filter would
I would never use the K and N filter off road, period. Stick with a good quality (genuine or equivalent) paper filter, and keep using the snorkel sock as needed. They will stop the paper filter from getting too caked, but there should be no reason you’d ever need more air flow than the factory setup, unless you’ve changed turbo’s or have done other substantial power upgrades.
All the best