Cold temperature Biodiesel question
 

Can someone explain to me how blending biodiesel with regular diesel work to prevent gelling at cold temperatures? I ask this question in view of my current observations of samples of biodiesel and biodiesel blends setting on my porch rail the last few weeks as the temperature fluctuates between 50 F and 20 F.
I have four samples of biodiesel (that I made with different lots of used cooking oil) and one sample of 50/50 blend. At 50 F (even down to 30 F) the straight biodiesel samples are all clear except for a thin layer of fine white precipitation that resulted after the first hard freeze (28F). As the temperature drops below 30 F a white flocculant forms in each of the four BD samples although all have different amounts at different temperatures. For example this morning at 24 F one sample was completely "gelled", a second was completely gelled except you could see small areas of liquid, the third was three quarters gelled and the fourth only about one quarter gelled.
Previously I observed the same results but noted that as the weather warmed all the samples would re-liquify to a clear state.
Now the 50/50 blend will be clear until the temperature drops but a generalized cloudyness will begin to form at the temperature declines. As the temperature continues to decline not only will the fuel cloud but increasing amounts of white flocculant forms at the bottom.
I suspect that even with substantial regular diesel blends (B20) some flocculant will form since the various methyl esters (palmate, oleic, stearate, etc.) will gell at different temperatures irrespective of how low their respective concentrations.
This being the case what does it matter the blend because eventually the filter will plug unless the fuel is warmed somehow. Any comments?

In BD Petro blends the BD is diluted. In doing so space between BD molecules is increased enough that they have difficulty forming the crystals you refer to as a white flocculant.

Gell point in BD depends on the feed stock used because they all produce different ester mixes and some mixes will gell more easily. I would bet it has to do with the length of the second hydrocarbon chain.

The white flecks you see are more probably waxes and other long chain carbon molecules. Your filter should catch them, and they will redissolve and feed on through when the filter warms up. The real danger is plugging the filter in prolonged cold temps and temporarily shutting down fuel flow. But, if your filter sits on top of the engine as in the 7.3 it will be warmed by engine heat and should be OK once the engine warms up. The inline filter found on the 2004 6.0 pump, mounted inside the frame rail is going to be much more likely to plug up in cold conditions and will not be warmed up.