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Fuel System Flow

I am replacing the original fuel filter system on our coach with a Davco 382 unit. We have a 2003 U320 with the ISM engine. I have heard how fuel flows back into the fuel tank, but have not figured out the route. My questions regarding fuel flow are:
1) is the fuel sucked through the fuel filter? It looks like the fuel pump is upstream of the fuel filter.
2) if the fuel filter on the side of the engine is 20 micron (I think what Cummins told me), why is the Racor (I think that is the brand of the original system) something like a 7 or 10 micron filter? I would expect the smaller particle size rating to be closer to the fuel injection system.

Thank you
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel

Re: Fuel System Flow

Reply #1 –
I can't help you on the filter question as I am not familiar with a 2003 but the fuel is sucked through the filters then pumped to the injectors and the excess fuel then goes to the fuel cooler then back to the fuel tank.
1999 40 ft. U-320 wtfe build 5563 Chuck & Lynda's "Rollin' Inn"  2030 watts solar
prev. mh's 71 GMC 5 yrs. 73 Pace Setter 1 yr. 78 Vogue 5 yrs 81 FTX 40ft all electric 18 yrs. 1996 Monaco Signature 3 yrs.
2014 Grand Cherokee Overland
Dream as if you will live forever. Live as if you will die today.  James Dean

Re: Fuel System Flow

Reply #2 –
Ed,

Normal fuel flow with our set up would be:

Tank, Davco (primary fuel filter with  10 to 30 micron element), lift pump, secondary fuel filter (fine 2-5 micron-- depends on engine specs which vary by type of injection system, even for the same engine) then engine/injection system.

There is a return line from the head or injection system (again depending on what injection system) back to the tank.

And, for every gallon of fuel through the system, you only burn a few ounces.  The rest is used for coolant and lubricating the injection system and head.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel System Flow

Reply #3 –
Quote from: wolfe10 –
...for every gallon of fuel through the system, you only burn a few ounces.  The rest is used for coolant and lubricating the injection system and head.
Super interesting.  Had no idea.
Mark Duckworth
2003 U320 4220
Build 6199, Motorcade 17971

Re: Fuel System Flow

Reply #4 –
Quote from: Mark Duckworth –
Super interesting.  Had no idea.
That fact (fuel being used as a coolant) caught me by surprise also, when we first bought our coach.  Somebody on the Forum suggested I hold my hand on the side of the fuel tank when it is about 1/2 full, right after a long hard run on the highway.

IT WAS HOT!

One of the several good reasons to never let your fuel tank get too low - more fuel in the tank equals better cooling capacity.

1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Fuel System Flow

Reply #5 –
Quote from: Chuck & Jeannie –
That fact (fuel being used as a coolant) caught me by surprise also, when we first bought our coach.  Somebody on the Forum suggested I hold my hand on the side of the fuel tank when it is about 1/2 full, right after a long hard run on the highway.

IT WAS HOT!

One of the several good reasons to never let your fuel tank get too low - more fuel in the tank equals better cooling capacity.



And, why some of us fit a fuel cooler (really a Hayden transmission cooler) in the fuel return line.  Because the fuel tank is "indoors" it does not get the cooling most other fuel system do.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel System Flow

Reply #6 –
Quote from: wolfe10 –
And, why some of us fit a fuel cooler (really a Hayden transmission cooler) in the fuel return line.  Because the fuel tank is "indoors" it does not get the cooling most other fuel system do.
I know Brett installed a cooler on a previous coach. Excellent idea and good point about our tanks being "indoors."

Perhaps even more important for the Detroit 2 cycle operators as the DDEC II ECU (Detroit Diesel Electronic Controls second version and Electronic Control Unit) have a fuel line running through it to cool it. Keeping the tank towards the full side will allow more heat to be radiated from the tank resulting in lower fuel temperatures running through the engine computer. Detroit operators with the Pro-Link 9000 tool can monitor the ECU fuel temperature as they drive. Since the 6V-92TA engine has no external fuel lines with all of the fuel running through cylinder head passages, the returning fuel is much warmer than on a Cummins or CAT diesel.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: Fuel System Flow

Reply #7 –
Thank you for the information, sounds like I need to add a fuel cooler to my upgrade list. Will try to keep the fuel tank level on the high side until then.
2003 U320 4010 - SOLD
2014 RAM 1500 Ecodiesel

Re: Fuel System Flow

Reply #8 –
Quote from: Pierce & Gaylie Stewart –
I know Brett installed a cooler on a previous coach.

Hmm, if he did it on this coach, I have NO clue where it is. Wonder how to spot such a good idea?
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Fuel System Flow

Reply #9 –
Quote from: mike leary –
Hmm, if he did it on this coach, I have NO clue where it is. Wonder how to spot such a good idea?

Gee, I think I know. 

Passenger's rear. Outboard of the CAC and radiator.  Dianne made a cover you could velcro on so it did not "over-cool" in the winter.  Just remove the ?6? ss phillips screws to access it (they are threaded in METAL, not just the fiberglass).

When you find it, post a picture for others.

Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel System Flow

Reply #10 –
Is this the panel I should be looking to remove to find the "cooler"?  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Fuel System Flow

Reply #11 –
Quote from: mike leary –
Is this the panel I should be looking to remove to find the "cooler"?  ^.^d

Yup.

Remove the lower grill (3 screws on each side-- leave top and bottom in place) and shoot a picture of the Hayden transmission (aka fuel) cooler.  All you do is remove the fuel return line from the engine and attach it to the "outlet" side of the cooler.  Then, new fuel line from engine to "inlet" side of cooler.

Again, on winter, just use the cover with velcro to keep fuel from being over-cooled.  Including R & R of grill, takes about 4 minutes.
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel System Flow

Reply #12 –
Thanks, Brett, will open it up, always wondered what was going on behind the panel. I assume when Dianne made the cover, she embroidered "hey rookie, it's right here."  ^.^d  ^.^d
1993 U-240 "La Villa Grande"..CAT 3116 w/ Pacbrake PRXB...Allison 3060 6-speed..
Previous: 1983 Airstream 310 turbo diesel, 1979 Airstream 280 turbo diesel
                                      Build # 4297
                                      PNW natives
                      Home base:  'Cactus Hug' (Ajo, Arizona)
                        DW Judy & Chet the wonder dog
                        Full-Timers 'Sailing the asphalt sea'

Re: Fuel System Flow

Reply #13 –
Well, what is behind the lower grill is (in order of air flow/from outside to inside):

Fuel cooler
CAC (Charge Air Cooler)
Radiator
Hydraulic cooling fan
Engine room
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel System Flow

Reply #14 –
You probably already have one... Our 99' U270 has one that has been there since the coach was new. I don't believe it was an option added by the original owner (we are the 2nd owners of our coach). If I am not mistaken, I believe that all of the Unicoaches 99' and up have them. The fuel cooler should easily visible through the grill in front of the CAC/Radiator Assy. as it is the outermost unit. As Brett says, they look like any typical transmission cooler.
Don
Quote from: Ed W –
Thank you for the information, sounds like I need to add a fuel cooler to my upgrade list. Will try to keep the fuel tank level on the high side until then.
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Don & Tys
1999 U270 3602 WTFE #5402
Xtreme Stage 1 w/Headlight, Step Conversion, etc.
2009 Honda Fit Sport with Navi
Freedom is NOT "just another word for nothing left to lose"... with apologies to Kris Kristofferson

Re: Fuel System Flow

Reply #15 –
Each engine and the injection pump it's fitted with will have a maximum fuel temperature somewhere in the specs. Some digital tools will readout the temp on the electronic engines so it's easy to see how it compares. An IR gun aimed at the side of the tank or down the filler should give a fairly accurate fuel temperature. Good to check the in and out temp on a fuel cooler too. Might be interesting to read the tank temp when a quarter full against the full temp if outside temps are close. Naturally, it would have to be on a different day.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)
 

Re: Fuel System Flow

Reply #16 –
Simply amazing how much there is to learn here...everyday!
Randy (N4TDT) and Karen Crete
Sarasota, Florida
SOLD:  2000 U270 34' WTFE Build 5756 "Ole Red"