About 5 years and 22,000 miles ago I fitted an inline fuel filter between the fuel pump and the fuel injectors, so the fuel is filtered before it reaches the injectors. In the standard system the Mahle KL167 filter/regulator is fitted after the injectors and filters the return fuel before it returns to the tank. It is in that position so that it does its job as a fuel pressure regulator, not so much as a filter. The filter I fitted is a Bosch F5316 (or Mahle KL83) that is normally for a VW Polo, fairly compact and will work with the 58psi fuel pressure.
I replaced it recently and cut it open to see what it had collected in the 22,000 miles of use. A surprising amount is the answer, the pleated paper filter had just a few small bits in it ( possibly from my cutting it open?) but was very discoloured and dark, certainly worth stopping the dirt there rather than letting it go to the injectors. I originally fitted a new filter/regulator (KL167) at the same time. I would normally replace that at 20,000 miles but will leave it for another 10,000 miles or so as it will have much less filtering to do and the pressure regulation is still spot on. I would say that installing an inline filter before the injectors is worth doing, after looking at what the filter has stopped. That said, we don't seem to be having lots of blocked fuel injectors, so maybe a solution to a problem that we don't have?
Check the KL167 filter/regulator for corrosion under the clamp, particularly if you don't have any insulating tape between it and the filter. There have been cases of them leaking with corrosion holes, fuel under pressure!
![[Linked Image]](https://www.tm-img.com/images/2026/01/31/Filters.jpg)
