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Topic: Fuel Gauge Calibration (Read 1566 times) previous topic - next topic

Fuel Gauge Calibration

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

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 –
Quote from: fouroureye –
I never want to put more than 110 gallons in my tank for the following reasons :headwall:

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 –
Quote from: fouroureye –
I never want to put more than 110 gallons in my tank for the following reasons :headwall:

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 –
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 –
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 –
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 –
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 –
Quote from: JohnFitz –
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 –
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 –
I don't know when Foretravel started putting fuel coolers in, our '99 has one

Re: Fuel Gauge Calibration

Reply #12 –
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 –
 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 –
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 –
Changed the pickup to then then new electronic style since discontinued and it reads correctly.

Re: Fuel Gauge Calibration

Reply #16 –
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 –
Yes I tilt the coach for full filling and to standardize the fill amounts for mpg calculations

Re: Fuel Gauge Calibration

Reply #18 –
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 –
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.