poly in the fuel filter...?? - PeachParts Mercedes-Benz Forum

wilburtual · #1 08-30-2011, 03:08 PM

recently i have been getting faster than usual clogging of my spin on fuel filter in my 1981 240D. ive been running wvo for over a year almost 100% and my wvo is very clean- centrifuged and filtered again to 1 micron.
the primary plastic filter doesnt clog, but when i take off the spin on filter, there are chunks of poly visible..!!! i assume this is what is clogging the filter/making the car sluggish- it gets better when i change the filter, but ive clogged 2 filters in 2 weeks....

ive never had a problem with poly in the past, anyone have any ideas/advice as to why i am getting this? i did have to put some diesel in the tank a few weeks back, which the first time it wasnt 100% wvo in a while... i wonder if the diesel stirred up some poly thats been forming in the tank..?
its a single tank system with injection line heaters and an inline 12v heater before the primary filter. there is no filter heater or tank heater.
if the poly is coming from the tank, how is it getting past the primary filter??
here's what the filter looked like when i took it off:

Biodiesel300TD · #2 08-30-2011, 03:18 PM

Has our oil source changed at all?

oldsinner111 · #3 08-31-2011, 06:26 PM

Its due to animal fats.In the winter 28 degrees and under I filter my best oiil.Cause animal fats turn solid,and I end up with pure oil.Being Summer now and warmer temps,animals fats flow thru your filters.Only to be caught at spin on filter.Been there done it.

wilburtual · #4 09-01-2011, 02:34 PM

my oil source hasnt changed, and there realy isnt any solid fats in the source, that i can see,,, i've had bad fatty oil in the past, but now its all liquid and i settle everything and just skim off the top liquid into a centrifuge.
i wonder if a filter heater would help keep things flowing in the filter,,? im just worried the chunks are coming from somewhere else, since they really looked like coagulated poly chunks in there rather than just a think/clogged filter of gooey fat.i've never spun it off and seen poly chunks before??

Biodiesel300TD · #5 09-01-2011, 03:23 PM

Are you cold filtering or warm/hot filtering. If you cold filter you'll filter out a lot more stuff. Anything that's thick at ambient temps will get filtered out. I cold filter my oil and it's crystal clear and I've never had filter issues. My last two Veg filters have lasted nearly over 10k miles.

GregMN · #6 09-02-2011, 10:50 AM

First: I have to say that I am not a fan of single tank systems. You will kill your engine prematurely. The injectors will spray WVO at 160 degrees in the same pattern as they do diesel. Colder than that and the pattern degrades to a dribble that does not burn completely and ends up on the cylinder walls. This will eventually clog the rings in their grooves resulting in loss of compression and allowing more and more WVO past the rings and into the crankcase diluting the oil and waring out all bearing surfaces.

OK. Now that I've gotten that out of the way....

Poly is formed in VO with time, heat, and air. It is accelerated with a catalyst.
Mild steel is a known catalyst. Your fuel tank is made out of mild steel.
If you are returning your unused fuel to the tank, you are adding heat and agitation (air) to the fuel in the tank.

Once you get poly starting to form in your system, it seems to start to grow at an accelerated rate. I have had this "infection" once in the E300D at about 100,000 miles of WVO use. Just emptying the tank and changing filters did not cure in the infection. Filling the tank with diesel and running that out did not cure in the infection. I removed the tank. Washed it out with soap (dawn) and very hot water until the water coming out was clean. I rinsed the tank out. I used a shop vac with a hose on the end that fit in the sending unit hole to get as much of the water as possible sucked out. I left it sitting in the sun dry out. The whole process took one afternoon. It completely cured the problem.

I suggest that you route the return fuel line back to "T" into the fuel source line with a manual valve to switch between "return to tank" and "loop to fuel source". Keeping the fuel in a loop in the engine compartment will allow it to heat up more as it continually comes in contact with your injection line heaters and the hot injectors.

When running on diesel only, the fuel needs to be returned to the tank. Hot diesel will not lubricate the injection pump as well as needed.