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
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.
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.
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.
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
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.
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.
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.
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
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
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
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
Simply amazing how much there is to learn here...everyday!