Community Forums

cponlinenv · 09-04-2017, 09:52 PM

I've had my 2008 Monaco Diplomat w/ 400 Cummins 8 months, so I'm still learning. On a 440 mile trip (220 each way) I ran out of diesel on the return leg. I didn't fill up at the destination because only two mini-marts had diesel so I planned to fill up at a truck stop on the way back at around the 350 mile point. That didn't work! I ran out of fuel 30 miles from my planned refueling point. With a supposed 100 gallon tank that means I got 3.2 mpg. Even though 1/2 of the trip was thru the Cascade Mountain pass each way I kind of expected 5 to 6 mpg. At 5 mpg, a 500 mile range would leave me with a fairly good cushion.

Food for thought: The fuel gauge read just under 1/2 tank. The service station brought me 20 gallons of diesel and when I fueled up (about 30 miles down the road) I could only put in another 40 gallons of diesel. And the fuel gauge now showed full just like it did when I started out. PS, ran the generator only about 1 hour on the way back.

I'm not sure what to think. Is 3.2 mpg through a mountain pass and back reasonable and the gauge is way off? Could the gauge be correct but the fuel pickup NOT picking up the last half of the tank? Could the tank be damaged somehow so my tank only holds 60 gallons? I haven't inspected the tank yet As an aside, power seems a bit down after the incident. Got back over the pass, but at a slower speed than going. Going over 40 to 50 mph. Coming back 35 to 40.

What I'm hoping the good guys on the forum can help with is an ordered list of things to check. I'm not diesel knowledgeable, but I follow instructions really well.

Right now it's in the shop for a new awning that I ordered and scheduled before the trip. I should get my coach in the next day or so and start troubleshooting then. As a precaution I think I should replace the fuel filters right away.

Thoughts?

Skip426 · 09-04-2017, 10:46 PM

Motor home , class A , fuel tanks are rectangular and may even have a data plate attached . If you don't find a plate , then measure carefully and you can calculate capacity .
100 gal fuel tank should have 90/93 gal usable , but with your 20+ 40 gal to reading full/ topped up , there are possibilities as you've described ; bad pick up, poor venting etc.

It is possible with running low/out of fuel , sucked up crud from the bottom of the tank and your fuel filter ( s ) are plugged.

adamfolger · 09-04-2017, 10:57 PM

Change the filters....

Flyin4Fun · 09-04-2017, 11:42 PM

I get 7.2 mpg lifetime average w/ my 400 Cummins (Monaco Dynasty 42'). Through mountains on I-75, the worst I have seen is 6.4 during a 110 mile stretch... then back to 7.1 or 7.2 mpg.

While it's in the shop, pay for them to run engine diagnostics. It would be money well spent. $100 to $200 is my guess.

cponlinenv · 09-05-2017, 12:08 AM

Good idea getting a diagnostic done. I've yet to settle on an engine shop. Guess I'll have to pick one. Would it be best to go to Cummins to get the diagnostic? I was leaning toward an independent that Paul Everett's shop foreman recommended.

oldguy70 · 09-05-2017, 04:39 AM

On my 98 Dynasty I ran out or fuel with at least 50 gallons of fuel in the tank. We had
gone around along entrance to a freeway turning right so the fuel was away from the
pickup. Also the fuel pickup was at least 6 inches from the bottom of the tank. When I
got home I pulled the tank built a sump and now my pickup is below the bottom of the
tank. When I took the pickup tubes and the return tubes apart the soldering was really poor and it's lucky that they hadn't failed. I go 800 miles without fueling and usually
have enough left in my tank to go 1000 miles, except the last tank as I'm getting poor fuel mileage as the engine is really running cold so I will put new thermostats in to day.
I get between 7.2 to 9 miles per gal.

twinboat · 09-05-2017, 05:12 AM

Do change the fuel filters after running out of fuel, you never know what's been sucked up. Pretty much standard practice.

There is a possibility that the generator and engine fuel pickup lines have been crossed. The generator one is shorter by design to keep from using up your " get to town " reserve.

The MH may have had some fuel tank work and on many, the fittings are the same.

YC1 · 09-05-2017, 06:09 AM

I agree with pulling the pickup tube for inspection. You probably can swing the fuel cap area out of the way by removing a few screws alone one edge. You may find four hoses. Two for the generator and two for the engine. I extended my generator tube because it was too short. However, early on the generator would die at unexpected times and conditions. I found the clamp on the hose at the tank was loose. This was a factory fault but I fixed it myself of course once found.

I would change fuel filters immediately of course.

As for any error codes, do you have the "message center" monitoring system? It is a elongated device about two inches high and 10 inches wide. It can give you things like error codes, fuel mileage, etc.

Busskipper · 09-05-2017, 06:36 AM

Quote:

Originally Posted by twinboat

Do change the fuel filters after running out of fuel, you never know what's been sucked up. Pretty much standard practice.

There is a possibility that the generator and engine fuel pickup lines have been crossed. The generator one is shorter by design to keep from using up your " get to town " reserve.

The MH may have had some fuel tank work and on many, the fittings are the same.

This would be my Guess - as it seems that you used about 3/4 of a tank but your milage would still be way off.

Sounds like you will have a major project before you travel - I can't imagine not being able to go at least 800+ miles on a tank (My tank is 150 so I'd have 40-50 in reserve)

It appears that you went around 410 miles on say 56 gallons or 7.2/ gal?

So usage is close to right - check with your mechanic - likely he will want you to use 1/2 the tank of fuel so he only needs to deal with the other half (still 50 gal)

Will be interesting to find out what the issue was - Yes change filters.

Best of luck - let everyone know what you find - ????

cponlinenv · 09-05-2017, 10:49 PM

Get it from the coach shop on Wednesday. They don't do engine, fuel system work. I'm going to take a look at the recommendations made here myself and go from there.

Found a shop to check out my fuel delivery problem if I can't figure it out myself following the recommendations from the forum.

barmcd · 09-06-2017, 06:49 AM

I think my 2000 has a 140 gallon tank, but only 118 is usable. Its a little confusing, but that's what I deduce from my owners manual.

DGBPokes · 09-06-2017, 07:34 AM

I don't disagree with any of the suggestions above. Fuel filters for sure. I would also comment, I am frustrated with poor quality of the fuel gauge in my Spartan chassis: it is very unreliable. So much technology in a modern rv, and the gauge accuracy of a Model T was better than mine. I never ran out, but sweated blood the first two times I made a long trip when it said I was running out and couldn't find fuel.
I have a long accurate history of MPG, and know I have a 100 gallon tank. I reset the odometer mileage every time I refuel, and use it for refuel planning.

robisinwa · 09-11-2017, 09:47 AM

Similar thing when I was new to having a diesel pusher... where on the old V10 Sunova I could take the gas gauge down to red line, the first long trip in the Monaco I ran out of fuel by trying to go below a 1/3 tank left on an incline. So many things are different with a diesel!

And related ... carry spare fuel filters with you, never know when you might need them!

Kurt Averill · 09-11-2017, 10:51 AM

I have a 200 gallon tank - 178 usable on flat level ground. I use the VMS to track fuel, I have found it to be very accurate, as long as you allow for generator usage which of course it does not track. The factory gauge says empty at about 100 gal. if the generator runs out of fuel you have about 15 miles to get to a fuel stop.... seems the pickup tubes are close to the same length. I had to change the filters and run a bunch of power service (additive) through mine to make it happy after running it out of fuel - the emergency road service people brought me out fuel in an old cross bed tank - was about 10% water judging by the amount I got out of the filters - and with the pickup tube that high off the bottom of the tank - who knows how much is still in the bottom. been using the additive religiously hoping to get that out. can't get the pick up tube out without cutting out some welded in brkts and sliding the tank out about 18", or cutting a hole in the floor. One way or another, its on the list....