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Old 04-04-2010, 03:35 PM   #1
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Tiffin Owners Club
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How much does my fuel tank really hold?

Okay, so my fuel tank is supposed to hold 150 Gals. Anyway this past week I let the tank run down past the "low fuel" warning and continued driving. Finally I got to about an 1/8 inch from the bottom of the gauge. When stopping an additional dash light would light showing a fuel pump. So I stop in the next station I could find and pump 114.241 gallons in the tank. I tried to squeeze as much in as possible and pumped until the foam was coming out, it was full.

So, are these Spartan MM's really programed to leave you with 35 Gals while scaring you into filling? Anyone else have this issue and or remedy?
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Old 04-04-2010, 05:05 PM   #2
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FWIW When I was on a tour of the Monaco plant in Elkhart IN a couple of years ago, I watched them build the fuel tanks. I asked the capacity of the tank and the response was that the capacity of the tank as measured by the outside dimensions was 100 gallons. However, due to the placement of the fuel inlet only about 85 gallons would ever fit in a level tank. He also said it has been a bone of contention between marketing and engineering for years. Obviously this may not apply to other manufacturers.
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Old 04-04-2010, 07:02 PM   #3
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I'd sure like to know how many gallons I can hold. If safety were not an issue I'd take a 300 tank just like a Peterbilt!
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Old 04-04-2010, 09:07 PM   #4
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Wardy: If you can get to your tank, hereís something you might try.

Figure the cubic inchís of the tank by multiplying length by width by depth. Then divide that answer by 231. Hereís the key, 231 cubic inchís equals one gallon of fluid. That would get you well into the ball park to the size of the tank. I donít always believe what a manufacture might print or say so Iíll pull this trick jutst to see how close itíll come to what they say.

Just an idea if your interested.

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Old 04-05-2010, 01:57 PM   #5
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I may do that Marty just for the heck of it. But I'd like to know about others with the same chassis and what they find. My gauge does not drop in a linear fashion. Once it hit's the 1/4 level it drops very quickly.
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Old 04-07-2010, 03:16 PM   #6
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I've always wondered that too. I've taken mine to 125 gallons or so but I'm not sure how far it can actually go. I do know that I can fill the tank so full that the fuel is in the fill tubes, which are higher than the tank so I'm sure I can get it full.

I've watched the trip computer readout when getting to that level and counted down to an estimate of how many miles are left. The problem is that that red light comes on and the trip computer says "low fuel" rather than how many miles you have left so you are flying by the seat of your pants after that. I try to remember what I had left and do some quick math in my head before the miles-to-empty display reverts to the "low fuel" message. Generally I "think" I have miles left to go but the gauge laying on "E" gives me an ulcer and I chicken out.

If I had a reserve tank and switch I'd like to take it to the limit but I don't and pushing 45,000 lbs isn't something I'd look forward to doing and my new puppy isn't quite up to that strength level yet.
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Old 04-08-2010, 04:32 AM   #7
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I tried also to toggle the display to read miles till empty, but you're right it will only read "low fuel". Also after I filled the coach I again checked miles till empty, divided that by my current MPG and I figured 146 gallons in the tank, who knows.

Really it feels like my gauge is from the 70's, non-linear. And like you mention the thought of running out of fuel in a 45,000 lbs vehicle is not pleasant. It's hard to over-rule a nagging gauge.
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Old 04-24-2010, 05:16 PM   #8
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The tank on my first motorhome, Southwind started seeping from the bottom. When I took the tank off, I saw that it was rusted out. Manufacturer wanted $1000 for a new one, not including the shipping and installation. I went to a welding shop who tried to repair it, but it was rusted too bad. He told me he could build one for $400. I told him to go ahead and do it. He told me it would hold 90 gallons. I told him the mfg stated the old one held only 75 gal. He showed me how the fill tube went down about 4 inches in the tank and limited the capacity. He built the new one flush with the top and it would hold 90 gal. The do that so you don't overfill the tank?
Well,when I traded it a couple of years later, I bet that was the only MH with a lifetime aluminum tank.
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Old 05-12-2010, 02:17 PM   #9
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I have the same issue with my fuel tank. I have a 2010 40' Phaeton with the Power Glide Chassis. The brochure for the Phaeton which is written for the Freightliner Chassis says the tank is a 100 gallon tank.

On my first trip, I drove until the gadge registered 1/4 full. I was able to get approximately 45 gallons on each fill-up. Based on this, I must have a 60 gallon tank or a very bad calibration on my fuel gadge.

Does anyone know what capacity my tank should be?

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Old 05-12-2010, 07:19 PM   #10
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I'll be watching this thread as well. We took possession of our new 2010 Phaeton on the PG chassis on 4/6/10.
I ran it down to 1/4 left on the gauge and only filled it with 53 gallons, so I'm curious as well.
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Old 05-24-2010, 12:34 PM   #11
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I've never gotten more than 110 gal on a fillup with my '08 Bus that is supposed to have a 150 gal tank. I remember being a bit fidgety on that fill because the guage read so low. I guess I was so happy with the final bill for the fillup that I lost my consternation over the amount of fuel.
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Old 05-24-2010, 12:45 PM   #12
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I have owned two motorhomes with Spartan chassis and one had a 100 gallon tank and one a 150 gallon tank. I ran out of fuel with the first one as I was pulling into a truck stop that had a hill going to the pumps. I carried diesel fuel back to the motorhome, primed it and then pulled to the pumps and filled up. It took 92 gallons to fill it up so that was 8 gallon short of the 100 gallon tank. But if I was not going up a hill I would have made it to the pumps.

I have put 128 gallons in my 150 gallon tank and I have no idea at what point it will run out of fuel and I don't want to know. On both of my motorhomes the low fuel light came on when there was suppost to be 30 gallons left in the tank. I.E., when the low fuel light came on it took 70 and 120 gallons to fill them up.
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Old 05-31-2010, 06:07 PM   #13
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A week ago I put 124.03gal into the Bus. The needle was pointing at 1/8. This calculates to about 8 gal un-indicated reserve, but this seems reasonable. This is on a Freightliner chassis. I had an 05 Diesel bounder that had a confirmed 10 gal un-indicated reserve, so things were consistent. I'm not too comfortable going lower than that, but my gauge and warning light are accurate.

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Old 05-31-2010, 06:57 PM   #14
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My '04 Phaeton's tank is rated at 100 gallons but is effectively an 80 gallon tank since you can never actually fill it to capacity unless you fill it then let is sit for about an hour then top it off.

My bladder is not very large either so I need to stop more often than a 100 gallons would allow so it's another of life's little irritations that I've adjusted to.
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