How long have you been blending biodiesel? Biodiesel will clean varnish off the tank walls and fuel lines and send it downstream. Keep a couple of sets of filters in the car until this stops happening. Get the clear kind of small filter so you can see what's going on with the fuel.

Sixto
87 300D

I've been using bio in the car for a couple years now. This summer I ran about 75% bio with no problems. I've been running straight diesel from September to last week. I put in a clear filter and have a couple spares. I've been avoiding driving the past few days due to the weather. I'm careful where I buy bio - this was from a ASTM certified place up in Massachusetts where I've bought a number of times before. Is it worth siphoning out the remaining 10 gallons in the tank? Tim

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1987 300TD wagon 193,000 miles