Don't replace your air filter!!!

[rlaxton]

On the topic of air filters, found this little gem:

http://home.usadatanet.net/~jbplock/ISO5011/SPICER.htm

Interesting to compare OEM style filters with aftermarket brands. The quantities of dust let through are significantly different.

Richard.

[bruiser]

How bad is one spec of dust for a motor anyway.
Sureley it gets burnt and blown out the exhaust anyway.

Cant really see that it is that detrimental.

What is happening to these poor people that have filters only filtering 99%. Is there motor gong to blow at 250 000 k's

[ISUZUROVER]

so does the same apply with diesel fuel filters? no offence to the diesel boys but it is a rather "dirty" fuel, maybe u should start pouring dirt in your tanks?

No - filters for liquids rely more on sieving rather than air filters, so will clog.

[ISUZUROVER]

How bad is one spec of dust for a motor anyway.
Sureley it gets burnt and blown out the exhaust anyway.

Cant really see that it is that detrimental.

What is happening to these poor people that have filters only filtering 99%. Is there motor gong to blow at 250 000 k's

Much of the dust an engine sucks in ends up in the oil - there is not much that can be burnt in the dust.

As to the life of the vehicle...

It depends on the vehicle and the operating conditions. Most car engines that only ever drive on bitumen roads will likely be worn out by factors other than dust.

However tests on earthmoving vehicles and mining vehicles have shown a significant increase in engine life when the air filtration is improved. Most heavy duty engines have the oil analysed at regular intervals, to check that the engine is not wearing abnormally and that the filters are working effectively. If too much dust is getting into the engine the oil will have a high silicon content.

Air filters are least efficient at about 1 micron. Filter efficiency is tested on a mass basis with particles that range up to about 100 microns. 1 100micron particle has the same mass as 10000 1 micron particles. So a filter can have a very high mass based efficiency and still be letting billions of small dust particles into the engine, which can still be doing harm.

[ISUZUROVER]

examining the graph will also tell you that at 4kg of dust the pressure diff is double from new, this will show that, all other factors being static, airflow will be 50% compared to the new filter. This should be sufficient (depending on the vehicle) to cause a "noticable reduction in performance/engine efficiency"

NO

Pressure drop is not related linearly to airflow like that. Doubling the pressure drop will only change the flow rate by a quarter to a half of the previous value.

[ISUZUROVER]

best just change your air and fuel filters at around the recommended intervals I think is the best conclusion-no joke!!!
Oh and oil as well !!!

The whole point of me posting this is to show that many people are replacing their air filters too often. Large engines have pressure drop guages to tell you when to replace the filter, but most cars/4x4's don't, and replacing the filters too often can do more harm than good.

I agree with changing oil and fuel filters at recommended intervals (liquid filters work more on the sieving principle that air filters, and so will clog). When many oil filters have too high a pressure drop across them they will bypass, so the oil is not filtered.

[adam.s]

best just change your air and fuel filters at around the recommended intervals I think is the best conclusion-no joke!!!
Oh and oil as well !!!

The whole point of me posting this is to show that many people are replacing their air filters too often. Large engines have pressure drop guages to tell you when to replace the filter, but most cars/4x4's don't, and replacing the filters too often can do more harm than good.

I agree with changing oil and fuel filters at recommended intervals (liquid filters work more on the sieving principle that air filters, and so will clog). When many oil filters have too high a pressure drop across them they will bypass, so the oil is not filtered.

I've always been taught to service a car regularly and it will last forever --> so yeah that's the only reason why I don't really care about the oil filter not filtering "as good as it could".

It's filtering "enough" when the oil gets changed 5000km or less, with good quality oil

[F'n_Rover]

some questions ben -
my new motor has 3 thou clearance on the main and big end bearings.
i was advised to allow a little more bearing clearance for a 4x4 motor so that any dust / grit in the oil would be washed away with the oil flow and not be impacted into the bearing shells. i'm running a high flow oil pump to compensate for the added clearance.

this micron size level dust would i imagine be impossable to filter out ???

how much damage could it cause if its way below the 1.5 thou metal to metal separation distance ?

thanks

[ISUZUROVER]

some questions ben -
my new motor has 3 thou clearance on the main and big end bearings.
i was advised to allow a little more bearing clearance for a 4x4 motor so that any dust / grit in the oil would be washed away with the oil flow and not be impacted into the bearing shells. i'm running a high flow oil pump to compensate for the added clearance.

this micron size level dust would i imagine be impossable to filter out ???

how much damage could it cause if its way below the 1.5 thou metal to metal separation distance ?

thanks

While bigger particles have the potential to cause the most wear, small particles can also cause wear (even if they are not as large as the working tolerances of most parts of the engine). They are around in a lot larger quantities than 38 micron particles would be (0.15 thou), and when subjected to the shear forces the oil is subjected to can still wear away the metal surfaces. However, if you have a cyclonic pre-cleaner on your filter/snorkel, basically all the particles 20-25 micons and larger should be removed by that. If you have good filtration IMO I don't think the tolerances should vary between a 4x4 engine and a car engine for dust reasons (but I am not an expert on this).

[ISUZUROVER]

For those still doubting...

From Caterpillar

Filter manufacturers often say "dirty" filters are more efficient than new ones because dust cake buildup on the surface actually increases filtration.

http://www.cat.com/cda/layout?m=37499&x=7

[Shorty40]

Filter manufacturers often say "dirty" filters are more efficient than new ones because dust cake buildup on the surface actually increases filtration.

True - but it has to end somewhere. The engine needs air. And if the filter is so caked with shit that it is filtering the particals so well, no air will get in.

I mean you could cake the filter 100% in "dust cake buildup". Sure, no dust will damage your engine, but thats because it wont be running

So to summarise 2 pages of 'egg head' theory ...... A little bit of dust on the filter aint a bad thing ?

[OldGold]

Well surely logic would dictate if a 'dirty' airfilter lets in less air, it's letting in less dust too?
All the above is pretty insteresting stuff in how air filters work etc but I hardly see how it's a revelation to anyone

Again, really interesting stuff on a generally ignored topic but, cheers

[Shadow]

you guys are dicks

ISUZUROVER comes in and gives some TECH info on air filters which is very relavant to 4x4ing, and you bag him and make jokes of it.

grow up

[bruiser]

I agree, the info was good, and interesting.
It has changed my view on airfilter maintenance.

[Shorty40]

you guys are dicks

ISUZUROVER comes in and gives some TECH info on air filters which is very relavant to 4x4ing, and you bag him and make jokes of it.

grow up

Did someone upset you sweetheart

Maybe you are the dick for crying in the tech section ISUZUROVER has posted info and some people have questioned the theories, granted, some jokes have been put in but I dont think anyone has bagged him for it

In short, go fuck yourself

[Mark2]

My GQ TD42 has a pressure drop thing which 'pop's into a red zone when its time to change the filters. Its factory fitted, but some other GQ's I've seen dont have it.

The other proplem with changing filters too often is dropping dirt straight into the clean side when doing the job. Which is one advantage of the twin filter system in the GQ's - you change the primary filter more often than the secondary and dont drop dirt into the clean side. Downside, is, its a very restrictive system.

[lexi]

I have to say mates being from Scotland I thought the thread was brill from start to finish. IsuzuRover made his point and kept his dignity. The jokers are brill and typically Oz which is what makes this forum so different to anything in Uk. I mean it was similar to when the English Professor went to the Doc and told him about this terrible and severe irritation in the vicinity of his anal regions. Wee Scots fella goes in after him with same complaint " Doc ma arse is oan fire, any cream fur it".
Alex

[ISUZUROVER]

I'm glad that some people found the tech useful. There is hardly any tech on here these days as it is...

To SUMMARISE for those who may still have trouble with what I am getting at:

(1) the test filters in question sucked in about 6 kg of dust - over that whole time the pressure drop across the filter increased by about 0.6psi. However the filtration efficiency increased A LOT in terms of the number of particles being stopped from entering the engine.

(2) the 0.6 psi difference on a truck engine running 20+psi or so of boost would hardly be noticeable in terms of engine performance (would be more noticeable on a 4x4 diesel running 10 psi or so of boost).

(3) testing has shown that for engines operating in dusty conditions, the factor which effects engine wear the most is dust intake.

[mickyd555]

i was thinking about this today, and seeing as we shouldnt replace the filter. should a good quality filter and then just blow it clean with an air compressor do the trick??

[ISUZUROVER]

i was thinking about this today, and seeing as we shouldnt replace the filter. should a good quality filter and then just blow it clean with an air compressor do the trick??

This is what is done with industrial air filters - a reverse pulse of compressed air (opposite to airflow direction) is used to "regenerate" them when the pressure drop gets too high.

The only danger with doing this is it places a lot more stress on the filter fibres than normal filtration, so they can break, and cellulose (paper) filters that are used as car air filters are not as elastic as industrial filters (which have plastic or metal fibres).

So, if done carefully, it should be possible to clean the filter with compressed air (in the reverse direction to airflow only) once or twice, but after that I would throw the filter away.