Air Filter Research 1:
Air Filter Testing
Seal, flow and dust test of
Genuine Vs Ryco Vs Unifilter
Vs Donaldson FHG Cyclopac
Update October 2022: Donaldson have released a PowerCore air filter kit for the LandCruiser 200
Read a review and test HERE.
Paper vs Cotton vs Foam: How do air filters work?
Cellulose fibre filters (eg: factory filters, Donaldson etc) are made of various grades of dry porous fibre or synthetic materials, although they are generally known as 'paper' filters (and that's what I'll call them). Air passes through 'holes' in the 'paper', while particles are trapped, so it's the fibre material itself that stops the dust getting through, as opposed to an oily coating which is applied to foam and cotton filters. The filtering performance of paper filters doesn't degrade as more dust accumulates on the filter, although airflow restriction increases. Almost all cars, trucks and 4WDs have 'paper' filters from the factory.
Oiled-cotton (eg: K&N) filters are made of much more porous material, but have a coating of oil which captures the particles as they are drawn into the filter. They deliver greater air flow than 'paper' filters, although whether that results in better real-world engine performance is hotly debated. Because these filters depend on the oily coating to capture dust, their filtration performance can decline as they accumulate dust and/or if they are inadequately or improperly serviced. To my knowledge, this type of filter is not used in any OEM applications.
Oiled-foam (eg: Unifilter) filters operate in a similar way to oiled-cotton, although they are made of open-cell foam instead of cotton. Again, coated with a tacky oil to capture the dust as it passes through. The filter media is much thicker than oiled cotton though. As with the cotton filters, filtration performance deteriorates if the dust load overwhelms the oil, and it's vital that they are regularly and properly serviced. Oiled foam filters are used in the vast majority of dirt bikes, but very rarely found as OEM equipment on cars or trucks.
Testing methodology
Test 1: Airbox seal testing
To test the hypothesis that the 200's airbox has a poor seal, allowing dusty air from the engine bay to bypass the air filter, I decided to subject the airbox to a vacuum test and check for leaks.
I removed the airbox from the vehicle and sat it upside down. I completely blocked the inlet of the airbox. I then filled the overlapping join of the airbox/lid with water, then applied a vacuum to the outlet. The objective was to see whether the water would be drawn past the seal and into the airbox.
Test 2: Filter element testing
This test measures the amount of dust (talc*) that travels through the filter element itself. It does not measure the seal of the airbox, and therefore whether any dust can get 'around' the filter.
- I hooked up a Stihl blower/vac to the 'outlet' of the airbox. This machine will draw around 10 m3/min (375 CFM) through a standard filter. This is similar to the ISO rate for this size filter and roughly what 200's engine draws at full throttle/1800-2000RPM;
- I then installed a filter into the bottom half of the airbox and weighed the lower assembly and the bottles of talc;
- I then fitted the lid of the airbox and started the air flow, measuring the airflow through the filter;
- I then gradually fed 800g of talc into the airbox inlet over a period of approximately 6 minutes. Once the bottle was empty and the 6 minutes had elapsed, I re-measured the airflow then shut it down;
- I then removed the airbox lid, and re-weighed the lower assembly and 'empty' talc bottles.
Subtracting the 'post-test' weight from the 'pre-test' weight measures how much of the talc has passed through the filter. The airflow measurements indicate how much the dust restricted the flow of each filter. See the table below for the results.
I also took photos of the airbox lid after testing each filter, and washed the airbox and lid between each test run.
* See the sidebar about why talc was used.
Pros and Cons of the methodology
Be warned, this testing is not a scientific ISO standard test. But it is a comparison of the different filters under the same conditions, using the same dust. In the absence of a half-million dollar ISO test bench, it's the best I could come up with. Take the results with this information in mind, and decide for yourself how valid the results are.
Good points of this test:
- The testing uses the 200's factory airbox and filters;
- It uses a natural dust (talc) that is very similar in particle size to standard ISO dust;
- It uses suction rather than pressure;
- It uses an appropriate airflow rate;
- All filters were tested under the same conditions.
Limitations and issues with this test:
- The seal test used water, which obviously flows through a gap more easily than dust;
- The seal test applied a vacuum level far higher than would likely be expected to exist in the airbox;
- Weight measurements are to the nearest whole gram and airflow measurements are extrapolated/calculated from flow over a smaller area. Both are therefore much less accurate than an ISO test, although they are consistent across all filters;
- The dust test is unrealistically severe. You would have to drive for many hundreds of kilometres in very dusty conditions, to expose your filter to the amount of dust injected over a ~6 minute period. This factor is particularly applicable to the Unifilter because of the way it operates. More info on this below the results.
Why use talc,
and why 800g of it?
Talc is a readily available natural dust. It's extremely close in particle size distribution to ISO test dust, sitting between A2 fine and A4 course dusts (closer to course). See the graph below for typical particle size composition.
Its suitability is reinforced by comparing the results from my test to the official ISO5011 results (where available) of the paper filters tested. They are within 0.5% in each case.
800 grams was an arbitrary amount I chose to use, based on the size of available talc containers and on the amount of dust used in other tests. The Duramax ISO test used 574g on a filter slightly smaller than the 200's. The Unsealed test used 600g on a much smaller filter. I felt that using 800g would not only test the efficiency of the filters and reduce potential margin of error from using a small amount of dust, but also test the dust capacity of the filter and the result if that capacity is exceeded.
LandCruiser 200 air filter Test Results
Seal test
| This table contains affiliate links for which I may be compensated | |
| Filter | Seal result |
| Toyota genuine 17801-51020 | Pass |
| RycoA1634 (NEW) | Pass*(See text) |
| Ryco A1634 (USED) | Fail |
| Ryco A1634 (USED, w/ greased seal) | Fail |
| Ryco A1634 (USED, w/ extra seal) | Pass |
| Unifilter TT275 265S | Pass |
Results Analysis
The tables above don't tell the whole story. Please read on for my assessment and explanations of the results.
Toyota Genuine (17801-51020)
The genuine Toyota filter was the best overall performer of the filters tested in the factory airbox. The seal test was a solid pass, with no leakage and no movement of the lid against the base. The fact that the genuine filter has such a thick seal is most likely the key factor in this result.
In the dust test, the genuine element had the second-highest initial airflow (behind the Unifilter) and the highest post-test airflow. It also captured more dust than any other filter in the factory airbox, at 99.13%. This is a reasonable result, although not as good as a premium aftermarket airbox and filter assembly, such as the FHG.
See the photo to the right of the inside of the airbox lid after the test. Keep in mind that this layer of dust comes from just 7 grams of dust passing through the filter during the test.
I have asked Toyota for the details of the changes that have occurred in the factory element, and also for their claimed ISO5011 efficiency. I haven't received a reply as yet, but will update the article when/if the information is supplied.
Ryco (A1634)
As I'd been running a Ryco filter up until the testing, I decided to test both this used filter and a new one, to see what difference 6 months/10,000km makes to the seal, filtration and airflow performance of the filter.
In a brand-new state, the Ryco passed the seal test, but there was some movement of the lid and the base. I suspect that any deterioration/deformation of the airbox would have caused the result to be a fail.
There was nothing uncertain about the used filter result, however. It failed completely, with water flowing past even before the vacuum was switched on. Once vacuum was applied, additional water was quickly sucked in, and air could clearly be heard moving past the seal. If you run a Ryco in a factory airbox, then I strongly suggest a strip of sealing foam on the base of the airbox, to ensure a good seal is maintained over the life of the filter.
The dust capture performance of the new Ryco measured slightly below that of the genuine filter, but there was only 1 gram in it (less than 0.2%), which was certainly within the margin of error. So there is likely little or no performance difference between the two. The used version measured exactly the same as the genuine filter. The only potential issue with this filter is the thinner seal.
Effect of greasing the seal/adding an additional seal
- Greasing the seal: This made little difference to the seal performance on the used filter. It held water before the vacuum was applied, but quickly failed with suction. I would not recommend this as a 'solution' to poor sealing.
- Adding an additional foam-rubber seal: The addition of a foam-rubber door seal strip to the mating surface was highly effective. With the seal in place, the used filter passed the seal test under vacuum. It made no difference whether the seal was applied to the lid or base of the airbox. Although applying to the lid would theoretically offer a better seal, it also presents a danger as there is no downstream mesh filter on the 200-series (unlike the 70-series). So if the seal were to break or be dislodged, it would be drawn into the engine, potentially causing severe damage. This risk does not apply if the seal is added to the base of the airbox.
Unifilter (TT275 265S)
The Unifilter's dust test result requires some detailed explanation, so please bear with me if an oiled foam filter is something you're considering. Let me begin by saying that -before I began testing- I thought the Unifilter would do pretty well. Not because I had any evidence that foam was better than 'paper', but because I considered the 200's airbox and/or filter was possibly worse than typical automotive filters, given the dusting reports. I even went so far as to buy the complete Unifilter service kit for the test, because I thought there was a good chance that's what I'd be running afterwards.
However, very early in the dust test it became apparent that the Unifilter was not going to perform well. With less than 1/4 (<200g) of the talc applied, a fine mist of dust could be observed coming from the blower outlet. This had not occurred at any stage with the other filters. At this point, I considered ending the Unifilter's test. However, to remain consistent with the other filters, I continued to inject the remaining 600g, much of which passed straight through the filter.
The Unifilter's result comes down to the way oiled foam filters work compared to a 'paper' filter. With a 'paper' filter, dust continues to accumulate in the filter, no matter how much is added, or at what rate. The only negative effect of 'overloading' a paper filter is that eventually the airflow is completely blocked. However, because a foam filter depends on its oily coating to trap the dust, overloading the filter causes both the airflow and filtration performance to rapidly deteriorate. The dust then passes straight through the open-cell foam, with the oil content either having been totally dried up, or unable to recover fast enough to capture the dust.
Unifilter argue that the test I performed was invalid for three reasons:
The type of dust: I disagree. See sidebar/graph above.
The volume of dust: It's certainly true that it would take many hundreds (if not thousands) of kilometres driving in heavy dust for a vehicle to ingest 800g of the stuff. However, the filter began to pass obvious amounts of dust before 200g had been ingested, and that sort of load is quite possible in the 'real world'. Ryco, for example, say that their 200-series filter has a capacity of over 540g before restriction exceeds specifications. The purpose of using such a high volume of dust was also to test the capacity/restriction of the filter.
The feed rate of the dust: I agree that the feed rate I used (approximately 130g/10m3/minute) was very high compared to the ISO standard of around 10g/10m3/minute. While the high rate didn't negatively effect the 'paper' filters, it would hurt an oiled foam filter, and is not representative of sustained real world driving conditions, with the possible exception of brief periods driving through bulldust patches.
After speaking to Unifilter and pondering these factors, I decided to exclude the Unifilter's dust capture result, although I do believe the test identified some key drawbacks of oiled foam filters, namely their relatively low dust holding capacity and deteriorating filtration/airflow as the dust load increases.
I cannot say with certainty how well the Unifilter performs at more typical dust rates, although it would likely have been better than it performed in this test. Unifilter and some of their owners say they outperform paper filters, while some owners disagree.
Based on ISO5011 testing, oiled foam (and cotton) filters do not filter dust as well as 'paper' elements, and I am more inclined to accept this scientific evidence rather than anecdotes. Unfortunately, Unifilter also dispute the validity of the ISO5011 test regime when used with oiled foam or cotton filters, claiming that the dust application rate is excessive/unrealistic. On that I have to disagree. The ISO rate is only around 1 gram of dust per cubic metre of air, and I'm sure we have all driven in convoy conditions where the dust is well above those levels. The lack of any agreed scientific testing regime makes it very difficult to conduct an objective comparison of their filters compared to others. On their website, Unifilter reference a test which makes claims on the dust micron size captured by foam Vs paper Vs cotton. I asked them to provide a copy of the test, but have been advised that it's old/out of date.
I asked Unifilter if they would like to provide a response, and you can read it here.
Donaldson FHG Cyclopac (complete)
As expected, the stand-out performer in the dust test was the complete Donaldson FHG air cleaner. Despite being a 30-year-old superseded design, it let through around 1/4 of the dust of the best flat-panel filter. Just 2 of the 800 grams of talc introduced into the filter made it through, for a capture rate of 99.75%, compared to its official ISO efficiency rating of 99.9%. It also had the highest airflow rates both before and after the testing.
One very interesting aspect of the Donaldson result was how much of the dust ended up in the in-built cyclonic reservoir. An impressive 568 grams (or 71%) of the dust never even made it to the filter element, because it got spun away into the reservoir.
The downside? There's no way of fitting this air cleaner assembly under the bonnet of a 200.
Cyclonic and Foam Pre-cleaners
I've had one of the original "full view" cyclonic precleaners for many years, running it occasionally when in dusty conditions on my last three vehicles. Although I always noticed that it captured dust, I was never sure how much of a difference it made, and didn't run it religiously.
However, given the stellar performance of the FHG's inbuilt cyclonic precleaner, I thought I should revisit them. When I did a quick test of my precleaner using talc, it captured about 66% of the dust. Tested to IS05011, cyclonic precleaners capture 75-80% of dust. Either way, using a precleaner is a very effective way to reduce the amount of dust reaching the air filter. You might not like their appearance, but they clearly offer a massive benefit for engine longevity and primary filter life.
If you don't like the cyclonic versions, there are also oiled-foam precleaners available from Unifilter and Air On Board. I can't comment on their effectiveness, but anything that reduces the volume of dust reaching the primary filter can only be a good thing. The only concern with these filters is that they have a very small surface area, and would likely restrict airflow quite quickly in dusty conditions. Cyclonic precleaners don't have this issue.
Note that all precleaners add restriction, and cyclonic precleaners can also be a bit noisy at highRPM/throttle. So it's best to leave them off for the highway and only use them when in dusty conditions.
| The following precleaners are suitable for use with Safari snorkels fitted to the LandCruiser 200 | |||||
| This table contains affiliate links for which I may be compensated | |||||
 Donaldson Fullview |  Donaldson Top Spin |  Unifilter droopie |  Unifilter ram cover |  AOB filtered ramhead | |
| Suit Std/V-Spec | H000821 (*May require a band of foam tape around snorkel top to clamp properly) | H002426 (*May require a band of foam tape around snorkel top to clamp properly) | Large | STD (150x100mm) | Filtered ram head |
| Suit Armax | H000858 | H002394 | N/A | LRG (175x125mm) | N/A |
Conclusion - Where to now?
What did I learn? Well, for a start I discovered just how hard it is to conduct a comparison of air filters! Having spoken to a number of people in the industry over the last couple of months, I honestly think it would be impossible to conduct a test that would satisfy everyone.
When I decided to do this test, I was hoping to find a 'magic bullet'.... An obvious fault in the airbox or filter that would explain the dusting reports. But that didn't really happen, and the results are unlikely to end any arguments.
I know Unifilter believe in their product, and some of their users report very good results from their filters. Equally though, some disagree. But I cannot ignore what I observed or the Duramax ISO test results, and so I will not be running an oiled foam filter and can't recommend them. I won't advise not to run one either, in the absence of further testing. I'm a person who prefers scientific testing and evidence over unmeasurable anecdotes, and at this stage there is little or no such evidence to support oiled foam filters. This concerns me, because if the superiority truly exists, then it should be easy to prove using the universally accepted standard tests. If you do decide to go with an oiled foam filter, then it's vital to service it regularly and well. An improperly oiled, unmaintained or overloaded foam filter is absolutely useless.
Now, to the 'paper' filters...
The dust performance of the Ryco was almost identical to the genuine, although it's let down by its thinner seal. If you go with the Ryco, then I would recommend the use of an additional seal strip on the airbox base. Avoid applying the seal to the lid due to the risk of the seal being dislodged and sucked into the engine.
Toyota's filter could certainly be better, but it isn't disastrous. The genuine Toyota element in the factory airbox seals well, and has a reasonable filtration efficiency of just over 99%. But is that good enough? The result of the Donaldson shows that it's possible to do much better. Given that the success of the LandCruiser is based on its reputation for durability in extreme conditions, the air filter is something where Toyota should have strived to excel. In speaking to a few filter manufacturers, I was told that 99-99.5% is pretty standard for automotive filter efficiency, so it seems that Toyota have decided that 'average' is good enough for the LandCruiser.
It is worth noting at this point, that it doesn't take much dust passing through to leave a very obvious film on the 200's airbox lid. Look at the pictures above of the post-test airbox lids, and you can see that the dust layer from the 'paper' filters looks very substantial, even though it represents only 7-8 grams (less than 1%) of dust having gone past the filter. It's quite plausible that the 200's filtration is no worse than previous (round) LandCruiser filters, but that the dust is more obvious because of the large ribbed lid on the clean side, as opposed to the small, smooth round hole on previous intakes. Either way though, I think it should be better.
Unfortunately, at this stage I can't identify a superior replacement, so I'll be running a genuine airbox/element in combination with a cyclonic precleaner until I can find an alternative. This combination should deliver an overall efficiency of >99.5%.
Next steps
- I'll soon be leaving for a trip to the Cape. When I return, I'll be actively trying to find (or design) an alternative airbox that can use an industrial-quality filter element with an efficiency of at least 99.9%. That's the sort of performance Toyota should have engineered, even if it's beyond what's typical in the sector. At this stage, the issue is finding an air cleaner assembly that fits in the available space while delivering sufficient air flow. Look for an update in the 2nd half of 2019.
- If you want to know how different filter types perform generally, then have a read of the Duramax ISO5011 comparison that I've republished here.
- I have been speaking to Ryco, the owner of the only ISO5011 test machine in Australia, about the possibility of conducting a similar scientific comparison of various LC200 filters. This is something I would really like to do, because it would determine once and for all the 200's filter efficiency, and compare alternatives. They have not yet provided a price but have asked me to follow up with them later in 2019. Once I find out the cost, I will check interest and (if there is any) set up a crowd funding campaign to get it done.
Update October 2022
Donaldson have released an air filter kit utilising their renowned PowerCore filter technology. Find a review and test of it here.