Originally Posted by boatjames
However on 2QM15 the fuel return line feeds the fuel back into the fuel filter for more immediate re-circulation. So, that being the case, is pressure still not an issue?
IMO - very BAD practice and of little practical value for 'filtration':
1. causes backpressure against the high pressure pump. Can yield a too rich mixture, unless injector timing is 'readjusted'. return line should discharge to near 'atmospheric pressure'.
2. Too little oil flow in the return line to be of 'benefit'. Pressure too low for effective motive pressure 'across' the filter; filters require 'work' to make them operate with efficiency, therefore needing 'humongous' filter surface area to keep 'pressure drop' across filter 'reasonable' or 'choked' return flow. see #1 above.
Recommendation: If you have a 'crudy' tank that requires inordinate amount of 'filter change', use a separate / independent 'fuel recirculation polisher' ON the tank and 'unconnected' to the main fuel distribution system ... then the 'fuel distribution system' will 'hardly' ever become 'challenged' with debris, etc. Such a std. 'recirc polisher' system requires that you 'start' with a pristine / cleaned tank. On a small hp engine the Recirc polisher can be 'quite small'. The amount of 'tank turnover' filtered at ~10-20µM will keep the tank at approx. 'sub-micronic' sized particles - a 'mathematical trick'.
On a practical basis, if your current filter usage is small, the tank internals are clean, then simply remove the 'polish' filter on the return line; but, install gages on the 'racors' so you know 'when'/if to change them ... before you 'crud up' the 'racors' and stall the engine. ;-)