Hi
My recently acquired 2.0 sport mk 3 has a K&N filter according to the previous owner. Looking uder the bonnet the normal air filter box is there, the K&N is (I guess) sitting inside this and has replaced the normal paper one.
Is it worth leaving it as is or ought I to go back to a standard paper one as used by Mazda originally? there is a school of thought that the K&N will let more dirt through than the standard paper one.
Thanks
It will give you a higher volume of airflow into the engine, in the typical UK climate it’s unlikely to accelerate engine wear.
Someone payed a few quid for it (£40 ish maybe), so if you do decide to take it out there may be some resale value.
Personally I’d leave it.
I will give you a fiver for it 
Leave it in.
Just give it a re charge and leave it in
Don’t forget that anything that (supposedly) enhances performance must be declared to your insurance company.
I’d leave it in but I’d make sure that it’s cleaned and oiled in accordance with K&N’s recommendation.
I bought one for my NA. It has been in for about 12,000 miles and definitely seems to make the engine more responsive. When I checked on it last service it looked filthy much dirtier than the paper one ever was. Would therefore indicate that it is doing a good job.
Interested in your remarks, Robbie that it should be cleaned and oiled regularily. K&N reckon every 100,000 miles which seems ridiculous.
Is it as long as that? I was thinking more along the lines of 20,000 miles max! I’d do mine yearly.
K&N website says up to 50,000 miles…
Sounds like good advice - thanks
I thought the interval for cleaning/reoiling panel filters is much longer than cone filters; 100k miles for panel filters, 40k miles for cone. Over cleaning is likely to cause more more than good. Plenty of industry papers, looking at OE paper filters, showing that too frequent air filter changing can reduce engine life.
Aother reason Im tempted to remove it. I wouldnt really knw what to “declare” to the insurance. All I know is theres some sort of K&N filter in there.
How are they cleaned and oiled if I decide to keep it?
Thanks
I usually give my KnN panel filter a light clean with a toothbrush and a very light spray of WD40 every other service. every 4th service it gets a major clean and re-oiling. No engine failure so far for me
I very much doubt that a panel filter will enhance performance.
You can buy a service kit for K&N filters, which comprises a cleaner and oil.
Drop in panel filter in the standard air box dosn`t affect insurance or warranty. K&N supply a sticker that you should put on the air box to alert mechanics not to throw the filter away and confirming warranty compliance.
I have used these filters on many vehicles over many years and have nothing bad to say about them at all.
I`ll up that offer of a fiver [above] to a tenner if you do want to ditch it.
Leave it in
You can buy proper cleaning and re-oiling kits for K&N filters, both genuine and other makes which are often cheaper. It takes a little while as once the cleaning liquid is applied it has to be washed out and left to dry before re-oiling.
For some insurance companies it does unfortunately, even if it doesn’t affect your premium you should discuss ‘all’ changes to your car with your insurance company.
With ref. to the original post.
If the previous owner hadnt mentioned the filters existence the new owner would never have known to inform the insurance company as under the bonnet everything looks standard ?
You’re quite correct, doesn’t remove the obligation to know what modifications have been made to the car though and declare them to the insurance company, ignorance is not a defence and you wouldn’t want to find out too late that a technicality was going to deny you a payout.