TomJ,

My contention is that if there is no loss of power when the engine is under full load, there is no need to replace the fuel filters no matter how long they have been in use. Fuel filters actually filter better when they start to plug up, removing smaller and smaller particles up until the point they will not pass the molecules of fuel. At that point not enough fuel will pass thru the filter to supply the fuel the engine's need at full power, although it will run OK at lower power levels and start OK.

Fuel filters plug up proportiional the dirt or algae in the fuel used, not to mileage. Therefore a mileage standard of replacement times is illogical.

The primary filter in my one 300SD has been there since I got it five years and 50,000+ miles ago and is going to stay there until I notice some loss of power. The secondary would be there also if it hadn't got a hole in the can and started to leak fuel.

"Most owners of MB Diesels do not change their filters when they should" is because they are smart and know that fuel filters need to be replaced only as required as shown in the above test, not because they look dirty.

NOTE: filters can also be cleaned and reused. MB used to have a special tool to clean the fuel filter cartridge that went inside the old style permanent fuel filter. At today's labor rates, it wouldn't be practical, but if you do it yourself it is.

P E H