[Mgs] oil filter

[Paul Hunt]

It's an anti drain-back tube.  Together with the anti drain-back valves that 
should be in spin-on filters it prevents oil draining out of the filter when 
switched off, which would otherwise happen with an inverted filter, leading 
to longer times to get pressure when restarting.  However the valves in 
filters can be very variable in construction and quality, and poor ones will 
allow the oil to drain out more as the filter gets older, and some can be 
pretty-well ineffective from day one, see 
http://people.msoe.edu/~yoderw/oilfilterstudy/oilfilterstudy.html.  Volvo 
3517857-3/Mann W917 seem to retain the oil for their lifetime (3k miles in 
my cars), better than the Unipart/Champion/Halfords typically available in 
the UK which tend to tail off albeit it about 50% dearer.  Some Fram filters 
are reputed to be good but one I tried from a well known supplier in the UK 
were noticeably worse.  K&N Gold seemed as good as the Volvo/Mann but are 
harder to get hold off and twice the price.  One thing to be aware of is to 
make sure your filter is at least an inch longer than the tube, some filters 
that fit the thread are so short they tighten down onto the end of the tube 
which prevents oil pressure developing.

PaulH.

----- Original Message ----- 

> ... I see a small
> metal tube about 4 inches long that is press fitted into the threaded
> hole that the oil filter element screws down onto with the metal tube
> fitting up into the oil filter.  What is the purpose of this tube...