The Weak Link In RV Dash Instrumentation

December 7, 2012 by Lug_Nut · 1 Comment 

If you're new here, you may want to subscribe to our E-mail Digest or RSS Feed. We will then send you the stories that are posted each day in an e-mail digest. We use a service called Feedburner for delivery of these emails. You will receive an e-mail from Feedburner after you subscribe and you must click on that email to activate your subscription. Thanks for visiting and enjoy all the information!

RV.Net Blog Admin

RV Dashboards

A Lug_Nut Thought.  Dash instrumentation has become more and more precise over the years.  Complex informative data can be displayed with near pin point accuracy.  Full “Glass Dashes” like that used in aircraft today are finding their way and showing up on some high end motor coaches.  Digital readouts have become common place in everyday automobiles over the past decade.  Engine temperatures can be observed to the single degree as can speed, engine RPM, manifold pressure, boost pressure, transmission temperature and much more.  In the average vehicle, these multitude of real time data information readings are of little value, outside of a cool looking gimmick.  In most cases “Idiot Lights” would probably suffice.


However, for large vehicles, like heavy motor homes and truck trailer combinations, this information can be vital and of great value.  Observing various data trends and digital readout behavior while travelling, can reveal issues that require attention.  That attention may necessitate an operation strategy change, or, if necessary, a physical investigation.


But, there is one instrument that every vehicle has and is used daily.  It has not really evolved operationally over that available when we were born.  While some sensor changes have been made, it is still about as inaccurate as they were 30 years or more ago.  That instrument is the fuel gauge.



Every vehicle I have ever owned, or driven, seemed to have the same inaccurate tendency.  It stays on “Full” for many miles after topping it up, then, finally starts to drop. (This is somewhat understandable given the float is held to the tank roof until enough fuel is removed to allow unrestricted movement.)  The reading is then steadily decreasing over the next many miles.  Once the indicator gets below half full, the decent increases speed, not proportionally similar to its progression on the upper half, seemingly twice as fast.  Soon the need for fuel goes from soon to now!

This is an irritation only if you are driving a car or light truck.  You can usually easily get to a fuel station, even in very rural areas, on the couple of remaining gallons.   Not so with a large rig.  Two gallons might only get you 12 miles or so.  Adding to the inaccuracy of the displayed fuel level is the unknown, what is the burnable fuel level?  How much fuel is unburnable in the tank?  This is fuel that is in the bottom of the tank below the intake tubing end.  The pickup end of the fuel suction tube is often cut on an angle to increase the opening and reduce the possibility of becoming plugged with debris.  This angle somewhat increases the amount of unburnable fuel as air enters the tube above the lowest portion of the end.  Now throw in how level the vehicle is, as that will also affect it.   So, bottom line, you can’t be 100% sure how much fuel left in your tank is burnable.

Well, I don’t know how the unburnable fuel issue could be eliminated.  But, I do believe this would be far less an issue if you had an accurate proportional level readout.  This would go a long way to determine non-fuel starvation risk fuel stops.  

Now, I know the built in fuel monitors found on many vehicles now display “Miles Range”, “Gallons Burned”, etc.  Well, they too, are getting the majority of their information from the same inaccurate sensor in the tank.  Even an accurate fuel flow meter, which are not found on any normal vehicles, would not account for fuel used for an RV’s generator and possible diesel fired water/furnace appliance.

Perhaps the only solution would be to have a fuel gauge that could be user calibrated on a linear scale that could be set to best indicate the true level value.  There just seems to be a need for a far more accurate way to determine how much fuel there is in your vehicles tank.

What are your thoughts?  Has your experience been similar to mine?  Let’s hear from you.  Your comments are appreciated below.


Leveling with You on Fuel   -   Lug_Nut   -   Peter Mercer



[Slashdot] [Digg] [Reddit] [] [Facebook] [Technorati] [Google] [StumbleUpon]