flyswamper
Calgary, Alberta, Canada
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I'm still poking around on my new Motorhome. It is a 2011 Monaco Knight 40pbq. The engine is a Navistar... the Maxxforce10.
One of the things I've poked around on that surprised me just a wee bit was the fuel/water separator and filter. As best I can tell, the engine has what I'd call the "built in" (as in, built into the engine housing) filter cartridge fuel filter and there is a little arm you can pull to drain water/fuel from the separator/catch there.
Additionally, on the other side of the engine I see a Fleetguard FS1003 water separator (that looks like a filter too). It has a little knob on the bottom of it and a drain spout sticking down. I opened this briefly a few days after having the rig and instead of draining water or diesel, all I got was the sound of air sucking into the fuel line/filter. I cracked it open once or twice more with no liquids coming out and only air getting in and decided I didn't want to mess with it any more and didn't want a bunch of air in my fuel lines (wanted to enjoy my time at the lake camping).
My question is....
What do you think is the reason that cracking that open draws in air instead of draining fuel? perhaps there is a siphon/vacuum at that spot from it being higher than the fuel tank? Or is there another reason my few seconds of cracking the valve open didn't drain any fluids.
I'm not really scared to poke around to figure all this stuff out, but I'd also like to make life as easy on me as possible when doing so. Looking for folks smarter than me to make that little light bulb over my head turn on for this thing.
Thanks folks.
Constructive disagreement is encouraged. It is how I/we learn!
Dad,Mom, & 3 young'ns
Current Home (Calgary)
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wolfe10
Texas
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If the level of the fuel filter drain is above the level of fuel in the fuel tank, it WILL suck air as fuel siphons to the tank when the drain is opened.
Fill fuel tank and/or raise the front of the coach and/or lower the location of the primary fuel filter/water separator.
Brett Wolfe
1993 Foretravel 36' U-240
Cat 3116, Allison 3060
FMCA Forum: www.community.fmca.com/index
Caterpillar RV Engine Owner's Club: www.catrvclub.org
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flyswamper
Calgary, Alberta, Canada
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Thanks. That is kinda what I was thinking with my siphon comment. The filter/separator is kinda high. Not sure I've tried it with a full tank, but I'm kinda thinking it is probably high enough that even with a full tank I'd get siphoning/vacuum flow back to the tank.
If I wanted to drain water from this, I'm not quite sure how I'd best go about it. I suppose if I find there is a valve I can close between the tank and the separator then I could just close that and drain a bit. Not sure if that exists or not though.
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wolfe10
Texas
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Unlikely that you have a shutoff between tank and primary fuel filter-- very few coaches do.
Do you have enough hose on either side of the primary filter to move it to a lower location without a bunch of work. That is what I would look at doing. Ideal would be at tank level with half a tank. Too low and lots of fuel comes out when the filter is removed, too high and fuel siphons all the way back to the fuel tank. And adding a ball valve (compatible with diesel) at the filter inlet would be a great idea as well. If you did that, mount the filter low enough that with the valve open it would fill the primary filter as long as you open a bleed valve, but would not run out when changing the filter with the valve closed. And with this low location, opening the drain would force out any water or debris.
BTW, do you have a clear bowl on the primary filter. If so, you can tell at a glance if you even need to open the drain. If you don't have a clear bowl, look at converting to a filter/bowel with one that will fit your filter housing.
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flyswamper
Calgary, Alberta, Canada
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Thanks...good thoughts there. I'll have to look closer to see what my options are. Right now I think I'll wait for the weather to cool off a bit before I mess with any of that, but I may see about adding a valve and/or moving it as you suggest.
(I'm in Oklahoma right now and I'm used to the cooler weather of Calgary )
To answer your question ..... No, I don't have a clear bowl.
Oh.... and one thing I'm wondering about.... If I crack this open long enough to let a lot of air in and perhaps empty the fuel line between the separator and the tank, will I run into trouble with too much air in the lines when I try to run the engine or the generator? Or am I likely to have some in-tank pump (or similar mechanism) that will get rid of the air-in-the-line issue I just created?
Right after I messed with it the first time I ran the generator a bit and I'm pretty sure it was running roughly for a few seconds at startup even though I had only let a relatively minor amount of air into the lines. Would I run into trouble if I cracked it open a LOT more?
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bsimonds
Winnsboro, TX, USA
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wolfe10 wrote:If the level of the fuel filter drain is above the level of fuel in the fuel tank, it WILL suck air as fuel siphons to the tank when the drain is opened.
Fill fuel tank and/or raise the front of the coach and/or lower the location of the primary fuel filter/water separator.
Isn't there something called a "lift pump" at the tank and wouldn't the check valve in this pump prevent fuel from flowing back into the tank?
Bill Simonds
'99 Winnebago Ultimate Freedom
330HP "Yellow" motor
'94 K5 Blazer 4X4 toad
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wolfe10
Texas
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Bill,
Normal (correct) fuel routing is: tank, primary filter, lift pump, secondary filter, engine/injection pump. So the primary filter is on the suction side of the lift pump.
Could it be different-- yes, but not likely.
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flyswamper
Calgary, Alberta, Canada
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Looking at it again, it is clear that my primary filter is mounted fairly high relative to the fuel tanks. Unless I park on a really really steep hill, I don't see much of a way to drain the primary filter and prevent backflow from the separator/filter back to the fuel tank.
One thought that occurred to me were to move/relocate the primary separator to a lower elevation. But I'm lazy and I'm not a welder (although I know plenty) and that would probably require welding a small mounting bracket somewhere.
Another thought was to cut the fuel-line that leads into the primary separator and to install a shutoff valve just upstream of the separator. Doing that it seems like I could just turn off the valve whenever I wanted to drain a bit from the primary and avoid backflow.
Again, me being lazy and this rig being brand new I'm not sure if I'm gonna do that (or anything) at this point in time. Still researching I guess. It just kinda surprises me that you'd have a primary fuel separator setup in such a way that attempting to drain it just results in backflow to the tank.
The BIG unknown for me is if I were "brave" enough to crack that drain open for an extended period of time, what would happen. Would it siphon ALL of the fuel and any water back into the tank? Or would it only backflow for a little while and then I might get some water/fuel drain from it?
And more importantly, if I put a LOT of air into the fuel line at this point would I end up having a mess with having to prime the fuel system? I'd REALLY REALLY like to avoid that sort of a scenario.
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flyswamper
Calgary, Alberta, Canada
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Well.... I'm sitting here thinking about this issue again. It's still winter, the dealer has had my unit most of the winter just taking care of minor stuff we identified in the first 90 days of ownership (we told them take all the time they need, we aren't camping in the frigid/snow/icy weather at this time anyway).
My latest thought is that maybe I could jerry-rig up something to apply a wee bit of air pressure to the fuel tank while cracking open the water-separator valve. Can't look at my fuel-tank to see the venting situation, but if it isn't vented and can hold a wee bit of pressure maybe this would be a poor-mans way of bleeding a little fuel (and maybe water) out of the bottom of my water separator without relocating it to a lower spot?
I'm thinking maybe it's as easy as sticking an airhose "blower" attachment into the tank and holding a rag around the hose on the tank opening to apply whatever pressure my hands and the rag could manage (ought to be really small pressure differential) and have my son crack open the water drain. Guess I'd want to make sure my air line didn't add/blow water into the tank though!
Any thoughts?
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