How would one know without an oil presuure gauze? Does the idiot light come on upon start up? Isnt it's purpose is to solely filter the oil only? Btw since I do 4 k oils changes ( and I most likely will recieve some flack on this for doing 4 k changes - as a it is supposely a waste of money) - but remember those 540i sludge problems? I am meticulous when it comes to fluids and so I take no chances- oil and filter cost to me is $50.00- using mobil 1, a seize motor is 5-6 grand......
Hengst is my preffered filter and have had no issues at all. And if Imay add , I have compared an Oem filter to a Hengst and they is no apparent difference.