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FDC Engaged - Can you still burn WMO?

woodcutter

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What damage (if any) can be expected to the HH or IP if filtered waste motor oil is burned with the fuel density compensator engaged? I ask because while on vacation a relative decided to fuel my deuce up on WMO without the FDC being disengaged. Hence, it stalled on the road and is waiting for me to get it home. I can change the filters, bleed the fuel system and pump out the WMO. Is this neccesary? Suggestions? Gotta Love Family!

Thanks, Phil
 

patracy

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The deuce will burn WMO with or without the FDC. The FDC only controls metering of fuel for power reasons.
 

patracy

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How was the oil filtered? Did it previously live on a diet of WMO? For it to stop, it's likely the filters. But I question the quality of the fuel in the truck...
 

eagle4g63

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Do you drive it a lot? You do know you are suppose to change your fuel filters every 6,000 miles (every other oil change)

As Patracy said the Deuce will run on almost anything with or without the FDC........I think you need to change the fuel filters.

A quick way to check is to open the bleeder on the final fuel filter....turn on the main switch.....see if fuel is squirting out or just barely trickling out......obvious if the filters are starting to go.
 

eagle4g63

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I run mine on ANYTHING......veggy oil, trans fluid, gear lube, hydrolic fluid, motor oil....on an on.......I also only filter mine down to 10 micron then in the tank it goes......have to change fuel filters more often but.....the thing runs fine this way and have put over 15,000 miles on it this way.
 

woodcutter

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Eagle - The truck is a daily delivery truck for my firewood business. I did bleed the secondary and final fuel filters as per TM 9-2320-361-20. Fuel came out slowly. Last complete filter change was last October. About 4000 miles on the docket since then. I am/was concerned that because the FDC is engaged this might cause a grater issue. I do understand that with it engaged it is equivelanted to turning up fuel by about 1 full turn, ie. increasing fuel delivery.
 

eagle4g63

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Well, if it is anything like my truck and others that I have talked to.......The fdc actually works AGAINST you with the thicker motor oil.

The FDC turns UP fuel with thinner fuels....IE: Gasoline(low BTU's), it turns DOWN fuel for thicker fuels.....IE: Diesel(high BTU's).....however you actually need MORE fuel to get the same power output out of the motor with motor oil however the FDC sees this as a thicker fuel and assumes it is HIGH in BTU's like the diesel fuel and so it runs sluggish.........This is the reason so many people BYPASS the FDC when they want to run mixed fuel all the time, the trucks are just TOO dang slow for everyday use otherwise.

Anyway, as you noticed the fuel in the bleeder is comeing out slowly.....just change the filters and it will be fine, it seems you were at the end of your filter life anyway.

Also in case you wanted to know, a little tidbit of info: Fuel at the pump is only filtered to 10 microns......a human blood cell is a whopping 40 microns!!! You have way more patience than I do filtering you stuff so low.
 

Clay James

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Also in case you wanted to know, a little tidbit of info: Fuel at the pump is only filtered to 10 microns......a human blood cell is a whopping 40 microns!!! You have way more patience than I do filtering you stuff so low.
I didn't realize it was that small. I have a 2 micron on my filter setup which is the size of a bacteria! Guess my deuces will get clean fuel.
 

woodcutter

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Eagle, yes my thoughts were the same on how the FDC works in preportion to power output with different fuels. In the future I will probably bypass the FDC. I did'nt expect to get home and find the truck fueled by my WMO and dead/limping on the side of the road. I am mainly concerned that the wmo might have screwed something up in the HH or IP before I disengaged the FDC. It did start after my roadside bleed but stalled out 1.5 miles down the road. At the moment I need to get her running. Going down the road now to change all 3 fuel filters.
 

patracy

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.....IE: Diesel(high BTU's).....however you actually need MORE fuel to get the same power output out of the motor with motor oil however the FDC sees this as a thicker fuel and assumes it is HIGH in BTU's like the diesel fuel and so it runs sluggish.........This is the reason so many people BYPASS the FDC when they want to run mixed fuel all the time, the trucks are just TOO dang slow for everyday use otherwise.
Just wanted to clear a few things up from your statement Eagle.

Diesel has [ approx ] 138,500 btu's per gallon.
Lubricating Oil has [ approx ] 153,000 btu's per gallon
Gasoline has [ approx ] 125,000 btu's per gallon


Chemically speaking, the WMO has a higher mileage potential for contained energy. However, the autoigntion temp and cetane values are different as well as viscosity which affects flow and timing. (Heavier fuels do not flow as fast which reduces the injection event timing [When and how long the injector nozzle opens/sprays])

Also the military actually bypassed the FDC as a MWO. This was due to the fact that these engines were designed back during the vietnam war. The reason for the multifuel was to power a truck with an engine that could make use of any fuel available due to supply issues. The FDC "later in life" began to fail with it's seals. This lead to fuel contaminating the engine crankcase. (Thinning the engine oil leading to damage) Since supply issues had been overcome since the wars in which the multifuel was designed, the military opted to simply bypass the FDC and run strictly JP8 or Diesel.
 

eagle4g63

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Well, Patracy.......I can't seem to find what I did with my chart of all the different oils and fuels.....so I will take your word on it, cause I have been known to have things a little backwards before.

I could have swore that the used motor oil had a lower BTU than diesel.....like I said I've been wrong before.

I do agree with you about the viscosity also playing a large part in the affects of the fuels and the amount of fuel that can flow through the injector at a given timing.
 

Katahdin

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I suspect you might have other problems not directly related to the WMO. If you've never drained and cleaned the tank and pump there's probably algae sludge and floaties in there larger then 25,000 microns (25mm). Where algae comes into contact with water at the bottom of the tank the algae gets hard and forms pieces that look like rust. The slow filter drain might be from algae clogged drain cocks as well. My tank was nasty as delivered directly from GL. Cleaning it out was one of my best maintenance tasks I've done by far. I may clean the tank out again every couple years.

Yeah, I mix 10 micron filtered WMO in the tank with the FDC bypassed, no problems so far...
 

phil2968

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Thank you sir. Off to read the TMs and figure out where in the he!! it's at and how to bypass.
Need some help with it? I'll be glad to help you. It's easy.
Yours may already be bypassed, need to look at the lines.
Phone number is in the sig line.
 
Last edited:

woodcutter

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Came in about an hour ago. Replaced all fuel filters. She fired up and ran as before the introduction of wmo (no stalling/coughing or loss of power...yet) The filters did not look clogged, it is more likley that moisture was in the wmo. I had filtered it but had not cooked it in the 55 gallon drum via barrel band heater to disipate possible moisture.

When I purchased the truck I did in fact clean the tank, intake screens and checked all electrical connects. There was no algae contamination. This truck was not a GL purchase rather from a private seller. Dog Head thank you for your post, that same article I did in fact uncover during my search's on the site . That article helped me determined that my FDC was engaged. The disengageing of the FDC may be my next project, not that I find any contamination (yet) in the crankcase.

I know that many burn alternative fuels in their trucks, I am not convinced this is the best day to day fuel source for our machines. I am not knocking others. Yes it will work, and was designed to do so when needed in wartime. It certainley is a cost saving alternative to pulling up to the pump. Like some, I use my truck to put bread on the table. Sometimes we look for cost saving alternatives. Therfore, I began filtering as the wmo oil was free.

Just my two cents.
 
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