LJ78 (2L-TE) Fuel Filter Issue

[Gun Runner 5]

Here is the scenario: If I add a few gallons of biodiesel to a mostly full tank of commercial diesel in my 1990 LJ78 there will be no issues. If I add more than a few gallons ( 5 to 6 gallons) to the same mostly full tank, the fuel filter light will come on instantly upon starting. When this first started I changed the fuel filter and the light stayed out. The last time I simply drained the filter and the light stayed out. I have run a lot of biodiesel through the fuel system so I am fairly sure it is as clean as it is going to get and the fuel is top rate. My question is... can the fuel filter light be triggered by a slight change in viscosity or does it simply look at contaminant levels? Thanks.........................1978HJ45

 

[Radd Cruisers]

The switch is operated by a float in the fuel filter, if the bio has a substantially different SG, then the float might sit up higher with the bio and turn on the light.

Generally, the only times I have seen the filter light come on when using bio (customer's trucks), it's due to glycerin getting into the system from poorly processed bio (home brew & the local bio Co-Op).

~john

 

[Gun Runner 5]

Thanks John, The only thing I find puzzling is the fact that once the fuel filter light comes on ( usually within a few seconds of starting the engine) you can drain the filter and the light will not re-illuminate. I would think that if there was a problem with the fuel ( glycerin or other contaminents) the fuel light would once again come on when you started the engine after draining the filter. Everytime I have changed the filter or drained it, the fuel filter light has never illuminated for the duration of the fuel tank.
I have also run thousands of gallons of the same bio fuel through my "H" diesel with no issues. Again thanks for the reply
...............1978HJ45