841 Diesel Fuel Pump

[Matthew Blevins]

I have a 841 diesel fuel pump that wasn't pumping fuel. I took it to a shop for rebuild and he took it apart and the next day, told me it would be $400 to rebuild it. The pistons had seized up in it. Is that a good price? Also what lubricant would be good to add to the fuel to lube the pump since diesel fuel has no sulfur for lubrication anymore? This guy told me he uses transmission fluid, about 3 caps full per tank. Any suggestions?

 

[JDemaris]

The sulfur doesn't give lubrication. What happens is - the process used to remove the sulfur cooks out some of the lube and energy. Then, lube additives are put back in. Pump fuel has lube in it, but to be on the safe side, adding two-stroke motor oil is the cheapest way to treat your fuel.
Add at a 200 to 1 ratio.

I assume you've got a Roosamaster/Stanadyne D series rotary pump? If so, it has two small pump plungers. To repair undamaged but stuck plungers, all is needed is a $12 seal kit and a few hours labor. Most pump shops charge $400 for this, so you made out fine.

 

[JES2 in SWOH]

I use Marvel Mystery Oil in mine and it works great

 

[JDemaris]

The reality is, how does anyone really know what is working, and what works best - without testing?

Same reasoning with worn pumps. I worked in several pump shops, but rarely ever knew for sure what wore out any particular pump.

There was one comprehensive test done (that I know of) on metal wear in injection pumps. In that test, Marvel Mystery oil scored low, as compared to other additives. In fact, it made the fuel worse. Not sure why.

Additives are numbered, and the higher the number, the less cost effective. Here are three - one with best protection, most cost effective, and the 17th worse - Marvel Mystery Oil.

The U.S. standard for diesel fuel says a commercially available diesel fuel should produce
a wear scar of no greater than 520 microns. The Engine Manufacturers Association had
requested a standard of a wear scar no greater than 460 microns, typical of the pre-ULSD
fuels. Most experts agree that a 520 micron standard is adequate, but also that the lower
the wear scar the better.


# 1 2% REG SoyPower biodiesel
415 micron improvement.
50:1 ratio of baseline fuel to 100% biodiesel
66.56 oz. of 100% biodiesel per 26 gallons of diesel fuel
Price: market value

#7 Super Tech Outboard 2-cycle TC-W3 engine oil
Unconventional (Not ULSD compliant, may damage 2007 or newer systems)
162 micron improvement
200:1 ratio
16.64 oz/tank




# 17 Marvel Mystery Oil
Gas, oil and Diesel fuel additive (NOT ULSD compliant, may damage 2007 and newer
systems)
42 microns worse than baseline fuel.
320:1 ratio