Biodiesel performance update

[raunch]

Been running various blends of biodiesel for a few tankfuls and here is a little info on how it's going. First of all, I'm running a N/A 6.2 with no mods other than I had the secondary fuel filter replaced with a Racor unit that has a primer pump (more on that later). The blends I have run are 20%, 38%, and 75%. There has not been a significant change in MPG's and I cannot tell a power difference between the blends or straight petro diesel. The MPG's are holding steady around 15.5 for mixed driving. Last weekend I pulled my pop-up trailer (2500lbs) for about 220 miles of highway driving and got 15.75 mpg.

The old fuel lines were replaced with biodiesel compatable lines, but the return lines at the injectors were not replaced, and it did not take long for them to deteriorate to the point of severely leaking. One of them went, I clipped the end and reattached, drove about 45 minutes longer, and another line went. Same temp fix and I made it home OK.

The Racor unit leaks at the seal to the housing. Tightened it and it still leaks. Called Racor and they said that their seals are good for up to 20% biodiesel. It would be about a year before they come up with something better. The Racor is my 2nd set of fuel filters before running bio. The first run of 20% stared to plug the filters after around 250 miles. This second set is begining to plug I think, as cold starts have been a little harder than normal. Although that harder starts may be caused by the filter leak allowing some air in the system (is that possible?). I'm going to change the filters again tonight and see if there is a difference.

[93GMCSierra]

I doubt the seal leak is caused by the bio, I ran bio in my truck as was no changes from stock and unless the lines and seals are already old and brittle the bio should not affect them.

[raunch]

You may be right about the seal leak. When I changed the filter last night, the little rubber tube from the primer seems a little long and may have been stuck between the seal and the housing. I made sure it was out of the way when the new filter was installed. No leaks after a test run down the freeway.

[raunch]

Been running various blends of bio for about 3000 miles now. What I have observed is that MPG's are better at a blend of 16% BD (a 5 gallon can per tank) compared to blends with a higher % of biodiesel.

For example-last Saturday I headed to Montana pulling a small, light trailer. Left home with a 16% blend in the tank and got 16 mpg's between here and St. Regis. Not bad for a TH400 tranny. I added another 5 gal of biodiesel in St. Regis, topped of the tank with petro, did the math and it came to be a 25 % blend. After driving the same route back home with the same conditions (no headwinds, same speed, same weight-well less beer in the cooler)the truck got 14 mpgs. This is the second time I have observed this difference in MPG's between a 16% blend and a blend that is richer.

[93GMCSierra]

what about uphill vs downhill? or other variations that might change the equation on the drive home?

[raunch]

I did go over two passes (Look Out & 4th of July) but they are similar in uphill and downhill on both sides.

[trentc]

One of the Diesel rags ran an article on biodiesel about one year ago. They ran dyno tests on 100% and showed an increase in overall torque. even though GPM dropped.