Fuel Gauge Calibration

Topic: Fuel Gauge Calibration (Read 1342 times) previous topic - next topic

Fuel Gauge Calibration

March 20, 2017, 07:32:41 pm

The low fuel "idiot light" comes on when there is approximately 50 to 60 gallons of fuel remaining in the tank. The fuel tank capacity is 150 gallons. I understand the need for a substantial reserve for the generator and not letting the generator empty the fuel tank. I was just wondering how the calibration on my coach might compare to others who might have noticed the level that turns on their "idiot light".

Nick

Re: Fuel Gauge Calibration

Reply #1 – March 20, 2017, 08:39:47 pm

Nick, I think you will find that 149 galls is really 135 + as the total tank volume is 149 and the filler neck bottom is 3" lower which comes in at about a 15 gall loss. Mine too comes on early but figure there is around 35 left. The full reading is quite a bit past the right side of graduations on gauge.
JohnH

Re: Fuel Gauge Calibration

Reply #2 – March 20, 2017, 09:16:56 pm

I never want to put more than 110 gallons in my tank for the following reasons

I have no idea what's in the bottom of the tank
The return makes my tank very hot, and I don't like that

I realize there are other technical reasons... oh and in the 88 GV, I ran it down it did require a fuel filter change..

Re: Fuel Gauge Calibration

Reply #3 – March 20, 2017, 11:13:35 pm

Quote from: fouroureye – March 20, 2017, 09:16:56 pm

I never want to put more than 110 gallons in my tank for the following reasons

I have no idea what's in the bottom of the tank
The return makes my tank very hot, and I don't like that

I realize there are other technical reasons... oh and in the 88 GV, I ran it down it did require a fuel filter change..

More fuel=cooler fuel

Re: Fuel Gauge Calibration

Reply #4 – March 20, 2017, 11:32:39 pm

Quote from: fouroureye – March 20, 2017, 09:16:56 pm

I never want to put more than 110 gallons in my tank for the following reasons

I have no idea what's in the bottom of the tank
The return makes my tank very hot, and I don't like that

I realize there are other technical reasons... oh and in the 88 GV, I ran it down it did require a fuel filter change..

Why does not filling the tank effect what is in the bottom of the tank?
And as said, the lower the level, the hotter the fuel, more fuel, more ability to mix the hot return fuel with the cooler fuel in the tank and dissipate the heat from the tank to the air around the tank. The downside is after a long day driving, you will have a hundred gallons or more of warm fuel under your coach. Great in the winter, not so good in the summer.

Re: Fuel Gauge Calibration

Reply #5 – March 21, 2017, 06:28:33 am

I think he meant he never wanted to get lower than the point where it took more than 110 to fill the tank. So, about 3/10s of a tank. It was a little confusing.

Rich

Re: Fuel Gauge Calibration

Reply #6 – March 21, 2017, 09:58:02 am

Rich.. correct

I wouldn't get anywhere putting in 25-30 gallons at a t I me... sorry for confusion

Re: Fuel Gauge Calibration

Reply #7 – March 21, 2017, 10:52:09 am

Most diesels return fuel to the tank as part of the fuel system design. The returning fuel is hot. Big rigs have the tanks out in the airflow. Ours don't. Keeping the tank as full as possible means fuel going to the engine is cooler. Injection pumps like cooler fuel. Several members have installed heat exchangers in the fuel line to keep temperatures down. Our Detroit even runs the hopefully cool fuel through the ECU to cool it. Not as good if the fuel is hot. Low fuel level always means hotter fuel.

If your coach is a U280/U300 with the 150 gallon tank, you should have exactly six gallons of fuel per inch if you stick the tank. This is what I do if there is a question.

I don't understand your statement, "I don't know what's in the bottom of the tank." Whats in the bottom of the tank will find it's way to your primary fuel filter. It should have a plastic see through bottom and drain on it to check for water, etc. Keeping the tank full, three quarters full or half full will have nothing to do with what's in the bottom of the tank. A full tank may actually lessen the chance of algae growth as there is less chance of condensation draining down into the fuel and then providing an interface for the algae to thrive.

Better to have a hot tank in summer heating the coach interior than the engine drinking hot fuel.

Pierce

Re: Fuel Gauge Calibration

Reply #8 – March 21, 2017, 11:02:17 am

Nick,
I don't have an idiot light but when my gauge reads 1/4 full, the reality is it's about 1/2 full (always takes about 75 gal to fill). Not sure, but I think a lot of FT's are that way and FT may have done that on purpose. I actually like it that way - seeing the gauge drop below 1/4 makes me nervous enough to not delay and I've never run out of fuel yet - which is a major bummer if not dangerous depending on where it happens. Fuel temp is another good reason to fill early: extra wear on the injector pump is what would bother me. The engine manufactures actually have a "max inlet fuel temp" spec that the OEMs need to comply to.

Re: Fuel Gauge Calibration

Reply #9 – March 21, 2017, 11:45:23 am

Quote from: JohnFitz – March 21, 2017, 11:02:17 am

Nick,
I don't have an idiot light but when my gauge reads 1/4 full, the reality is it's about 1/2 full (always takes about 75 gal to fill). Not sure, but I think a lot of FT's are that way and FT may have done that on purpose. I actually like it that way - seeing the gauge drop below 1/4 makes me nervous enough to not delay and I've never run out of fuel yet - which is a major bummer if not dangerous depending on where it happens. Fuel temp is another good reason to fill early: extra wear on the injector pump is what would bother me. The engine manufactures actually have a "max inlet fuel temp" spec that the OEMs need to comply to.

John,
If you have a Pro-Link plugged in and zero the fuel MPG setting for trips, it will tell you at a glance while driving how much fuel you used since your fill up, MPG since fill up. Easy to determine exactly how much is left in the tank. I used a tape measure inserted into the tank but this is a lot easier. Also, it can tell you the fuel temperature so you can compare it to max allowable factory limits.

Pierce

Re: Fuel Gauge Calibration

Reply #10 – March 21, 2017, 12:23:31 pm

Pierce. My 88 was a steel tank. Got my filter plugged so yes im leary even with a stainless tank. To others point I get nervous when I put in over a 110 gallons, because I've been there.

If calculations presented are correct I figure I have 20-30 gallons remaining and the return is hot.

I try to fuel between 900-1000 miles which is around 100 gallons-that's me..

Re: Fuel Gauge Calibration

Reply #11 – March 21, 2017, 03:06:49 pm

I don't know when Foretravel started putting fuel coolers in, our '99 has one

Re: Fuel Gauge Calibration

Reply #12 – March 21, 2017, 03:44:44 pm

My 1996 U320 tank is rated at 150 gallons.
Careful measuring and dipping the tank, I concluded: Maximum fuel in tank is 142 gallons (filled right up to the neck).
The number of gallons per inch is 5.9.
Minimum depth of fuel to still run (on level ground) is 1 inch, so 6 gallons, however when climbing, need 2 inches or 12 gallons.
I use the Silverleaf gallons_used and dip the tank at under 50 gallons (generator gallons_used is not tracked by Silverleaf).
If in Canada where it is cooler, I refuel before 20 gallons left.
In California where it is hot, I refuel before 40 gallons left, or if tank feels hot to the touch.

Fuel gauge calibration takes patience, because it requires empty and full resetting two or three times (three tanks of diesel).
My OEM fuel gauge is very accurate, but others have reported that theirs is of little use.

Re: Fuel Gauge Calibration

Reply #13 – March 21, 2017, 03:50:50 pm

I figured on the safe side Wyatt and at 5.6 gallons/ inch as I too now and again do a dip measure. Have not looked at how to re calibrate the gauge to make needle stop at the full mark (when full of course)
JohnH

Re: Fuel Gauge Calibration

Reply #14 – March 21, 2017, 10:41:40 pm

My fuel gauge was reading inaccurately for the first year or so that I had my coach. When full, the gauge read about 5/8s of a tank. When showing just over a 1/4 tank it would only hold about 60 gallons. I searched the forum and found direction to "recalibrate" using the small screws on the top side of tank. I was waiting to fill up just before a couple day stop to do the adjustment.

One day I filled up using the passenger side fill port and suddenly my gauges started reading correctly. I assume that the sensors were either stuck or had gotten coated and no longer read correctly.

Point of post is to suggest you try filling from passenger side a few time prior to adjusting your gas gauge sender

Re: Fuel Gauge Calibration

Reply #15 – March 21, 2017, 10:56:07 pm

Changed the pickup to then then new electronic style since discontinued and it reads correctly.

Re: Fuel Gauge Calibration

Reply #16 – March 22, 2017, 07:07:06 pm

I thought most owners knew that you can use the leveling system to lean or tilt the coach and fill the tank almost to max. My coach will go almost 100 miles before the fuel gage moves off full, and when the low fuel light comes on it will only take about 90-95 gal. to fill it. When the fuel is low the greater chance of sucking air for either the engine or generator is when the coach is leaning over to one side as the pickups are in the center of the tank with the engine pickup just above the bottom of the tank. The tank is longer side to side than fore and aft and it's flat on the bottom. Most fuel tanks have a low spot for the pickup, but not ours. Ditto on all the comments about heat from the return on the injector pump.

Re: Fuel Gauge Calibration

Reply #17 – March 22, 2017, 07:24:39 pm

Yes I tilt the coach for full filling and to standardize the fill amounts for mpg calculations

Re: Fuel Gauge Calibration

Reply #18 – March 22, 2017, 09:41:34 pm

Bob, Yes, when I drop the driver's side, I can easily get another 6 gallons in when I fill to the top of the filler neck.

P

Re: Fuel Gauge Calibration

Reply #19 – March 23, 2017, 07:03:28 am

Either you guys are getting fuel very cheap or you are being paid to transport the stuff down the road. I'm not sure there is any place in the US that you can't get diesel every 200 miles or so and certainly every 500 miles if shopping for price. I very seldom take my tank above 3/4 full.

Re: Fuel Gauge Calibration

Reply #20 – March 23, 2017, 11:08:43 am

Condensation in the tank as it cools is an issue as is the fuel volume as a heat sink for the returned fuel.

A non full coach where we live in shaky town(Los Angeles) is not using the coach to its full potential if a emergency occurs...

Re: Fuel Gauge Calibration

Reply #21 – March 23, 2017, 11:17:31 am

Quote from: Caflashbob – March 23, 2017, 11:08:43 am

Condensation in the tank as it cools is an issue as is the fuel volume as a heat sink for the returned fuel.

Agree on both counts:

Particularly in hot weather, running on less than 1/2 tank materially raises fuel temperature. Fuel is used to cool and lubricate injection components. Because of their internal tank location, Foretravels are particularly sensitive to low fuel level causing elevated fuel temperatures. Hence, many of us have installed fuel coolers (basically transmission coolers) in the fuel return line.

And, if you have a 150 gallon tank and 50 gallons of fuel, you WILL HAVE 100 gallons of air. And at whatever temperature and humidity air you were driving through as you consumed that 100 gallons. When the temperature of the tank drops to the dew point of the air in the tank, the water will condense out. Being heavier than diesel, it will go to the bottom of the tank where it encourages algae/bacteria growth.

Yes, when on grades, the extra weight hurts MPG, but 600 more pounds of fuel in a 30,000 pound coach is really not significant. And, on flat land driving aerodynamic drag FAR outweighs the affects of coach weight on determining MPG.

Re: Fuel Gauge Calibration

Reply #22 – March 23, 2017, 12:03:59 pm

Quote from: lgshoup – March 23, 2017, 07:03:28 am

Either you guys are getting fuel very cheap or you are being paid to transport the stuff down the road. I'm not sure there is any place in the US that you can't get diesel every 200 miles or so and certainly every 500 miles if shopping for price. I very seldom take my tank above 3/4 full.

Out west, states like Nevada have far fewer major cities with less expensive diesel. Some more isolated roads will only have an occasional service station where trucking the fuel in means increased costs so I almost always use GasBuddy.com - Find Low Gas Prices in the USA and Canada to find the least expensive diesel ahead. After arriving, I drop the left side to get every ounce in that I possibly can. The up and down grades here also drop the fuel mileage down much lower than when you get east of the Rockies.

Agree, on flat land in much of the U.S. fuel prices are not that much different and fueling is available at much closer distances.

Pierce

Re: Fuel Gauge Calibration

Reply #23 – March 23, 2017, 05:05:11 pm

I have learned to phone ahead to verify gas buddy pricing. Occasionally incorrect.

Various state txes can make a larger purchase a savings

Re: Fuel Gauge Calibration

Reply #24 – March 23, 2017, 05:17:40 pm

Always keep at least 75%, got stuck in a hurricane a number of years ago. Ran the diesel genset in my bus for 12 hours a day for 3 weeks, had ac, hot showers, ice and cold beer, did run extension cords to many of my neighbors, to run fans or small refrigerators. Bus only had about 20 gals in it when i finally got to fill it up.

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