Quote:
Originally Posted by Texasgeezer
As I understand it:
The pre-filter is primarily to protect the lift pump from larger particles.
I believe most engines with lift pumps have a 'large particle' filter ( or should have one ) before their lift pump. Quite often it is a sock/screen in the fuel tank. The external one is an additional safeguard.
The pre-filter typically is not pressurized and is not rated to withstand pressure.
I believe a 20 micron pre-filter ( if small in size ) would plug up fairly quickly and impede fuel flow.
Last week while searching for a better pre-filter for my friend, I found NAPA and other parts houses typically don't care about microns and tend to sell filters with a low micron rating to be placed before the lift pump. This is wrong and would lead to fuel flow problems and the resulting low power or worse consequences. The prefilters should typically be a screen and not be cellulose or other low micron material.
This previous post says the old style 'L' shape pref-ilter is much larger than 20 microns:
http://www.peachparts.com/shopforum/diesel-discussion/239083-fuel-filter-micron-rating.html
That thread also says the WIX pre-filter is 20 micron plus a lot of other google hits says it is 20 micron.
Wix site says it is 140 micron:
https://www.wixfilters.com/Lookup/Exactmatch.aspx?PartNo=33006
I know there are typically no problems with fuel supply while using the Mercedes specified prefilter but I like to have a larger filter since they are plentiful and low cost and would catch more crud before impeding fuel flow.
I plan to replace the metal pre-filter I installed about 30,000 miles ago with the long clear plastic filter & also to try to "stand it up" so water would tend to settle towards the bottom and not pass on to the final filter. Plus the water and crud would be visible while the filter is clear. Just another safeguard in case a service station pumped a little water with their diesel.
The black fuel line is Gates 'barricade' 3/8". It fits over the snipped off Mercedes clear plastic fuel line that was going to the lift pump. Also bypassed the fuel heater since we live in a mild winter state. |
I have had my Mercedes since 2007 and even with the one tank full of bad fuel I have had I have never had the plastic (primary filter) plug up. If you are getting bad fuel or something is growing inside of your fuel tank you need to take care of that.
People have put between the Plastic Filter and the Fuel Tank another filter, usually a water separator that has a changeable element. If I had a 125 micron filter that is where I would put it.
I run the stock plastic primary filter (nominal 20 microns) and either a CAT 2 micron of similar Baldwin Filter in the modified Fuel Filter Housing with zero issues.
Filters are supposed to be change x amount of miles bit I don't do that. I wait till I have had some loss of performance of if the mood strikes me to change filters. However, I buy fuel at known places that have good fuel. I buy where the Big Rig Drivers buy.
If a Big Rig Driver gets a load of bad fuel he is on the Radio telling everyone he can to not buy from that station. That costs the Station big bucks. Hence those stations monitor the fuel quality.