The problem with the cheapies on diesel engine is pretty much what has been mentioned in the post above mine. If the fittings are too small, you will cause pressure build up in the motor and push oil out seals. The provent and ryco ones have 25mm inlet and outlet ports on them, the stock breather hose on the d22 yd25 is around 20mm from memory. I fitted one of the small forefront ones on mine and while it works ok, the ryco I have fitted to my patrol does a lot better job. With the forefront, I fitted a clear length of hose from the outlet of the can to the inlet on the intake piping. This was fairly well covered in oil on the inside, however, the ryco on the patrol has clear hoses on both inlet and outlet and while the inlet hose is getting pretty oily, there's nothing at all in the outlet hose. This will come down to the filtering media though as the forefront can runs a wound stainless mesh filter, while the ryco uses as actual filter paper type element.
In saying all that, ryco do make an apparently provent replacement filter to suit both small and large versions which I believe is made out of the same material as the filter ryco use in their own cans.
If i did buy a 1 litre one with 12mm fittings, could i just drill them out and put bigger fittings on?
Or will that change the filtration?
Or will a 15mm inlet outlet do?
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