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Topic: Fuel gauge accuracy? (Read 1359 times) previous topic - next topic

Fuel gauge accuracy?

Read a post in another section where they mentioned how accurate their VmSpec was for fuel consumption.  I have a mechanical gauge on my Oshkosh V917 chassis that reads 1/2 full but only takes 50 gallons in the 150 gallon tank.  When the gauge is down to about a 1/3 then I've still got 75 gallons of fuel.  As I remember it, I put in about 100 gallons at 1/8 of a tank. Of course, with the Cat 3208 I have no computer.  How good are your fuel gauges?
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Fuel gauge accuracy?

Reply #1 –
John, mine is pretty darn good.  I can generally tell within about 10 gallons of how much fuel we'll be needing before my wife heads in to talk to the attendant before I start pumping the diesel.  We have a '99 model.
Russell
'99 U320 CAI 40ft w/Xtreme Full Body Paint
Baton Rouge

The selected media item is not currently available."Tetons"

Re: Fuel gauge accuracy?

Reply #2 –
That might have been my post, Yes the VMSpc showed 105 gal used, Actual took 107 gal to refill and the dash gauge showed 5/16 remaining.
Was surprised how close the VMSpc was to actual.
I feel that is good calculating, set for the ISM450.
Dave

Re: Fuel gauge accuracy?

Reply #3 –
John,

What brand fuel sender unit do you have?  The Centroid units used by Foretravel (their own "chassis") are easily adjustable (small screwdriver) as to how long they read full as fuel is used-- the main cause of inaccuracy.

Brett Wolfe
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel gauge accuracy?

Reply #4 –
Brett, where is the adjustment made?  I have fuel tank fill on either side of the coach.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Fuel gauge accuracy?

Reply #5 –
Peter,

There are two tiny screws on the Centroid sender unit. One is sealed-- leave it alone.

The other adjusts the full/overfull setting.  It is VERY sensitive/small adjustments make a big difference.

Have a helper turn on the ignition (don't need engine running, just gauges reading).

With a full fuel tank, adjust the screw so that the dash gauge reads full, but not overfull.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel gauge accuracy?

Reply #6 –
Brett, thanks for the info.  I realize the Unicoach is a bit different from the GV set up.  Should the sender unit be reachable from the side of the tank?  Or is it located in the usual place where only midgets can get to it?
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Fuel gauge accuracy?

Reply #7 –
Quote
Should the sender unit be reachable from the side of the tank? 

Peter,
I am not sure about your location but as a reference here a photo of mine. Drivers side.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: Fuel gauge accuracy?

Reply #8 –
Gracias.
 
I'll look next time I visit the coach in storage.  My fuel gauge is definitely off as when it is full, the needle is way off the full mark.  Then it stays there for about 500 miles and drops off fast after that.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Fuel gauge accuracy?

Reply #9 –
Brett,
On the Oshkosh chassis the fuel tank is located between the chassis rails and seems like it is 10' long.  The fuel fill pipe is about 4' long and comes down at angle from the opening beneath the driver's window and then enters the tank half way up.  I never have understood how I am able to get it full (sort of, as I give up after a few burps).  Based on the Oshkosh drawing of the fuel tank the sender is located on the top of the tank and would require removing the tank to get at it unless Foretravel put in an access plate in the coach floor.
John Cooper
'91 GV 36'
Oshkosh chassis
Cat 3208T 300HP

Re: Fuel gauge accuracy?

Reply #10 –
John,

If you have trouble fully filling the tank, use the jacks to raise the side of the coach with the fill.  Makes it a lot faster and you can get more in.

Brett
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020

Re: Fuel gauge accuracy?

Reply #11 –
Quote
use the jacks to raise the side of the coach with the fill.  Makes it a lot faster and you can get more in.
I can get 10 - 12 gallons extra when I raise the side of the coach.
That is the only way I can get my 100% full reading on my (DIC) Drivers Information Center.
That way I am getting close to accurate readings when figuring out mpg as I am always starting from the same FULL point.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: Fuel gauge accuracy?

Reply #12 –
Peter,
Curb side fill nozzle and ("Centroid?") sender are side by side.  Right out in the open and easy to change/calibrate.
There is an old and a new style Centroid sender.  Both sender heads look identical.  The new style has auto zero (empty) circuitry while the old style had to be zeroed manually.  The new style is supposed to be MUCH more stable and reliable. 
My original started acting erratically, I replaced it years ago (with the original style), calibrated the replacement and it was great for 6 - 8 years.  Then last year it started acting erratically again.  I purchased a new style spare while in NAC, but recalibrated the second (installed) one and it has been fine ever since.  So just buy a spare and your concerns will go away.
I can send pictures and calibration instructions if you need them.
Regards,
Neal
The selected media item is not currently available.
Neal (& Brenda) Pillsbury
'02 U320 SPEC, 4200, DGFE, Build #5984
'04 Gold Wing
'07 Featherlite 24'
'14 Jeep Grand Cherokee Summit
MC #14494
Exeter, NH & LaBelle FL
Quality makes the Heart Soar long after Price is Forgotten

Re: Fuel gauge accuracy?

Reply #13 –
Neal,
 
Thanks for the information & offer.  If it's not any trouble, posting the pictures & instructions would be great for those of us who have similar coach vintage.
Peter & Beth Martin
No Forrest? What have you done?
MC# 15890 until Dec 2016; FMCA #F329677
Cincinnati, OH

Re: Fuel gauge accuracy?

Reply #14 –
Quote
Based on the Oshkosh drawing of the fuel tank the sender is located on the top of the tank and would require removing the tank to get at it unless Foretravel put in an access plate in the coach floor.

Foretravel did not make an opening in the floor of the coach. The tank will have to be dropped.
The Oshkosh sender is a float type sender, with ohms resistance depending on the gauge that was installed.
That is the correct procedure.
The selected media item is not currently available.Barry BEAM #16014
2003 U320 40' AGDS
Beamalarm, Foretravel technical help and specifications
"Whatever the mind can conceive and believe, it can achieve"

Re: Fuel gauge accuracy?

Reply #15 –
All,
I have put some pictures of the Old and New style sensors, as well as the Centroid Installation and Calibration procedure into an album in the Photos/Files section.  http://foreforums.com/index.php?action=media;sa=album;in=175
I had my facts twisted on a couple of items:
    • The two sensor heads don't look identical because the new sensor head does not have the "empty" and "full" calibration potentiometers..........it is strictly digital and programmable, as you will see from the pictures and procedure.
       
    • It's not an auto zero (empty) but actually an auto (full), start point, once the sensor has been programmed to a known FULL tank.  That should go a long way toward resolving the "flaky readings" that we often see during the top half of fuel tank usage. 
Once again, I recalibrated my old sensor and put some Loc-Tite on it, right after I purchased the new style, and the old one has worked perfectly ever since.  Carrying a spare sometimes has that GREAT effect!
However, I don't actually know if the new style is better than the old, as they (FOT) claim.  But, being digital and programmable seems like the right direction for improved stability.
Regards,
Neal
The selected media item is not currently available.
Neal (& Brenda) Pillsbury
'02 U320 SPEC, 4200, DGFE, Build #5984
'04 Gold Wing
'07 Featherlite 24'
'14 Jeep Grand Cherokee Summit
MC #14494
Exeter, NH & LaBelle FL
Quality makes the Heart Soar long after Price is Forgotten