Fuel gauge wonkie, really wonkie

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Fuel gauge wonkie, really wonkie

April 22, 2013, 02:26:21 pm

This is pretty long so, if you want to skip the story and the math just jump down to the last two paragraphs...

So I filled up near Casa Grande AZ, Friday evening and head East. When I filled up, I filled it FULL!!!

Started driving and it took hours and hours to get the fuel gauge just down to "F". We were still above Full when we stopped for the night. Then hours and hours to get down to 3/4 tank. Stopped for the night 2nd night (Saturday) and fuel gauge said just at 3/4 tank. 635 Miles since filling up. Ran the Gen for maybe an hour after we stopped so we could run the A/C. Woke up Sunday morning and it was pretty cool, so turned on the Aquahot on Diesel for maybe an hour to warm the coach back up.

Hit the road Sunday morning and that's when the fun began. When we took off, I noticed we were between 3/4 and 1/2 tank and thought that we had used a lot of fuel for 1 hour of generator and 1 hour of Aquahot. As I drove, I was guesstimating we used 20 Gallons of fuel over night???

That couldn't be right. The fuel cooled down and condensed? Maybe?

For the next two hours I was running up and down hills in West Texas. I set the cruise at 72 mph, there was a pretty good head wind but had no problem maintaining 72. However the fuel gauge was dropping much faster than the previous couple of days. Within two hours I went from 5/8 tank to 1/4 tank.

Roughly doing math in my head I was figuring 200 gals / 8 = 25 gallons per 1/8 tank. I figured I burned about 75 gallons of fuel in two hours or 37.5 gallons an hour. YIKES!!!! That's works out to roughly 2mpg

, can't be. Yachts don't burn that much fuel

. But we had been getting such crazy good mileage for the last two days, I didn't know what to think. At this point we getting low, could we make the next couple of hundred miles to where I had planned to fill up. Another 30 minutes on back roads between 50 - 60 mph and we were well below 1/4 tank. We had traveled 242 miles on this stretch. Time to get fuel.

***
Found a station that seemed to be the busiest in town and put in $100, or 26 gallons. I figured since I was between 1/8 and 1/4 tank I had between 25 and 50 gallons. Plus 26 should give me somewhere around 50 to 75 or 1/4 to 3/8 of a tank. Turned the key to find I was way above half. Off we go, as I drove for the next couple of miles the gauge went all the way up to 3/4 tank and settled back down around 5/8. Then dropped more reasonably over the next 75 miles to where we are now.

So, is this normal??? Is this why it's pretty common to hear people say they only run the top half of the tank? Or is the sending unit bad? Is there a float of some sort? Ironically all the fuel lines are new in the last year or two, but I started wondering if one of them might have a big hole in it.

Please let me know if you have any thoughts.

Douglas

Re: Fuel gauge wonkie, really wonkiehe

Reply #1 – April 22, 2013, 02:36:38 pm

I start with a full tank, then everything makes sense. Putting a few gal in would be difficult to get a handle on the amount of fuel in the tank. Seems either a full or empty tnk would be the only time you know for sure ?

Re: Fuel gauge wonkie, really wonkie

Reply #2 – April 22, 2013, 02:43:28 pm

Douglas, pretty normal with the gauges. First thing I recommend is to clean the contacts @ the tank. Not sure of your year and model, but if you have a 100 gallon tank I would drive it 600 miles then fill up...driving 72 does hurt your mileage about 1/2 gallon. Aquahot and generator use very little.. Gauges do jump around a bit.

I use mileage, gauge, and silverleaf to keep me out of trouble....After the 3rd time I ran out of diesel I finally learned my lesson.

FWIW

Dave has a great point

Re: Fuel gauge wonkie, really wonkie

Reply #3 – April 22, 2013, 03:45:26 pm

Our coach sat for almost nine years in storage, with 3/8 of a tank of fuel. The dash gage now reads 3/8 whether full or empty, altho we never let it get that low. We try to fill up around 300 miles on the odometer. Safer, as we have a 100 gallon tank and normally get around 9MPG.

Fuel gages are apparently poor indicators of actual fuel left. Better to fill up and drive off the top half of the tank. Estimate consumption by determining MPG and then use this ti determine how far you can go on 1/2 of a tank.

Re: Fuel gauge wonkie, really wonkie

Reply #4 – April 22, 2013, 04:11:45 pm

Here's my 2-bits. My 1990 U280 has a 143 gallon tank. It says. And after measuring, that's what it will hold if you stood it on end with the filler cap at the very top. So, after a couple of trips, I level the coach at the pump, then fill as close to exactly to the bottom of the filler pipe as I can. Since the tank holds 6 gallons per inch of depth, it's a little difficult to be precise on the fills. My calculations indicate that the bottom of the pipe is 130 gallons. 8 miles to each gallon that make for 1,040 on a tank. It's more than I can drive in a day, sometimes even two. But, that said, 1/4 tank is 210 miles. Driving 65, that's 3.5 hours without stopping for something interesting.

While moving, since the gauge is buffered somewhat, it will register slightly higher than actual content because it sloshes around.

It took me two trips, and a total of 1,200 miles to get comfortable with how that thing works. But it does.

Hope it helps.

Re: Fuel gauge wonkie, really wonkie

Reply #5 – April 22, 2013, 04:13:32 pm

I guess you can tell I didn't proofread the math. 1/4 tank would be 260 miles and closer to 4 hours on the road.

Re: Fuel gauge wonkie, really wonkie

Reply #6 – April 22, 2013, 04:23:44 pm

Our gauge was pretty flakey and unreliable when we bought our coach. I adjusted it a bit and now it is more reliable, but still just a relative indicator. I fill with fuel based on mileage, location, and plans. The sender can be cleaned, adjusted, or replaced. I recommend that you leave the gauge in place to fill a spot in the instrument panel, and depend on your odometer and habits to establish a pattern for adding fuel.

You likely have about 1200 miles of range from a full tank. Fill up before you have driven 800 miles. I choose to fill about every 400 miles of driving.

I watched the mechanics at FOT start the engine in my coach after they replaced the fuel lines. It was difficult to do even with the expertise and resources available in the shop. I NEVER want to run out of fuel in the coach.

Re: Fuel gauge wonkie, really wonkie

Reply #7 – April 22, 2013, 04:26:13 pm

I don't pay any attention to the dash fuel gauge.

My VMS-240CL tracks fuel used by the engine. I estimate AquaHot and generator fuel.

For VMS-240CL see: http://www.silverleafelectronics.com/?q=node/14

best, paul

Quote

This is pretty long so, if you want to skip the story and the math just jump down to the last two paragraphs...

So I filled up near Casa Grande AZ, Friday evening and head East. When I filled up, I filled it FULL!!!

Re: Fuel gauge wonkie, really wonkie

Reply #8 – April 22, 2013, 04:35:04 pm

Agree, get the VMSpc if you have an electronic engine, I depend on it for very accurate fuel readings.

Re: Fuel gauge wonkie, really wonkie

Reply #9 – April 22, 2013, 04:37:17 pm

The original owner of my coach had FOT repair the fuel gauge multiple times. It reads 1/2 when it is full and when I get ti 1/2 it is accurate from there down. At 8 mpg I drive about 800 miles and then fuel, I have run 925 miles til fueling. I am used to it now so I leave it be.
Gary B

Re: Fuel gauge wonkie, really wonkie

Reply #10 – April 22, 2013, 07:21:23 pm

My fuel gauge reads just over 1/2 when full, about 70 gallons left at 1/4 and it never goes lower. Like Dave I depend on VMSpc for accurate fuel consumption and fuel remaining. I start looking for fuel at about 80 gallons left. GasBuddy helps me find better prices near my route. I don't go very far out of my way to save a few cents. Access in and out of the station is at least as important as price. I got fuel in Austin, TX at a regular gas station. Almost an hour to fill up. Slowest pumps in the world. A truck stop fills you up fast and you are on your way.

Re: Fuel gauge wonkie, really wonkie

Reply #11 – April 22, 2013, 09:31:31 pm

Douglas,

Your fuel gauge is working the way it was designed. Like many car gauges, it is not intended to be linear. It moves very little in the upper half and moves very quickly at the bottom.

Re: Fuel gauge wonkie, really wonkie

Reply #12 – April 22, 2013, 09:46:24 pm

That sounds about right to me, I use the VMSpc, have a number of times make real close checks, and every time the actual gals used was within 2 gal, with very little generator running and no Aqua Hot use, now I just peak at the gauge on dash and chuckle, who knows where or what is indicates, full tank shows up at half, after running about 200 miles it goes to 7/8, by the time the VMSpc shows 100 gal left, gauge shows 5/16. Have the 194 gal tank.

Dave M

Re: Fuel gauge wonkie, really wonkie

Reply #13 – April 22, 2013, 10:09:40 pm

I've found two solutions to the fuel gauge issue. One is a wooden stick. Dip in the tank and pull it out. Not too sophisticated but pretty accurate. The other is to calibrate your Centroid fuel sender. Here's the instructions from Barry Beam's site:
Centroid Fuel Sender Calibration This info comes from the Centroid site at www.centroidproducts.com It takes some patience but you can get the gauge to read pretty accurately.

Also, you could have a problem with the Centroid itself. On our 225 the insulator on the inner tube had deteriorated and allowed it to touch the outer tube. Once I fixed that it read correctly. I had some photos of this fix but I can't find them. First the hair, then the memory. Good Luck.
jor

Re: Fuel gauge wonkie, really wonkie

Reply #14 – April 22, 2013, 10:11:53 pm

Yup...The fuel gauge is very erratic & inaccurate indeed. I adjusted mine a very tiny bit and it functions only slightly better. Too much adjustment and it's bye bye readings with any accuracy at all. So, like most I gauge the fuel by miles driven. After between 700 and 900 miles, I fill up. This is anywhere from 60 to 100 gals depending on fuel consumption per mile.

Re: Fuel gauge wonkie, really wonkie

Reply #15 – April 23, 2013, 12:48:32 am

Wow, I always get a huge number of responses to my questions. Thank you to everyone.

It's nice to know I'm not the only one who's fuel gauge is inaccurate.

So, with the 198-ish gallon tank sounds like filling up every 800 miles is a pretty good plan, should rarely get below 1/2 tank. That should also keep the fuel charges reasonable chunks.

Re: Fuel gauge wonkie, really wonkie

Reply #16 – April 23, 2013, 01:49:43 am

Quote from: ScubaGuy – April 23, 2013, 12:48:32 am

Wow, I always get a huge number of responses to my questions. Thank you to everyone.

It's nice to know I'm not the only one who's fuel gauge is inaccurate.

So, with the 198-ish gallon tank sounds like filling up every 800 miles is a pretty good plan, should rarely get below 1/2 tank. That should also keep the fuel charges reasonable chunks.

There is an little adjustment screw on the edge of the tank for the last 1/2 of the tank in the gauge. Mine said less than full now reads over the full on the gauge. Bottom screw is what I understand was adjusted on mine.

Re: Fuel gauge wonkie, really wonkie

Reply #17 – April 23, 2013, 08:22:58 am

I drive a maximum of 800 per fill however I don't like the nervous feeling that I may not find a service station so I try to fill up between 500 and 600 miles just to be safe. I have gone well over 800 without running out of fuel. I just consider the fuel gauge a general guide and reminder just like the Silverleaf.

Re: Fuel gauge wonkie, really wonkie

Reply #18 – April 23, 2013, 08:56:23 am

Silverleaf GOOD (do not forget to reset)
instrument panel gage BAD

Re: Fuel gauge wonkie, really wonkie

Reply #19 – April 23, 2013, 01:43:59 pm

I have only had one accurate gauge in my life. It was on a 1953 Austin A30. When the needle reached "E" the engine stopped. All the rest just seemed to be suggestions. I like to "drive on the top half" and refuel at 1/2 tank. As a boat owner I have always been aware of fuel consumption so I look at the miles I am going to drive and work out needed fuel and allow a good reserve. Have not run out of fuel since the A30 days.

Keith

Re: Fuel gauge wonkie, really wonkie

Reply #20 – April 23, 2013, 03:39:44 pm

Mine is very accurate when full, and show full for at least 100 miles, then it starts bounding back and forth, full to empty, for a long time until I get fuel. Keep telling DW that I am going to fix it one of these days. At least I don't run out of fuel all the time like her "truck driver" father did.

Re: Fuel gauge wonkie, really wonkie

Reply #21 – April 23, 2013, 08:19:53 pm

Kieth you bring tears to my eyes as I had an A30 and an A40 later. I taught my mom to drive in the A30. Got it when I was an apprentice at 18 and was only able to afford petrol for it to go out twice a week. It sat in front of parents house but I could look out my bedroom window and see "my car"!!
John H

Re: Fuel gauge wonkie, really wonkie

Reply #22 – April 24, 2013, 05:59:51 am

Mine was very inaccurate, I replaced it (easy fix) 2 years ago and calibrated it per the instructions. Now it is spot on as guages go, with the coach sitting level 149 gal tank 1/2 tank =65-75 gallons. I try to fuel before the 1/4 mark, running out of fuel is a major PITA.

Re: Fuel gauge wonkie, really wonkie

Reply #23 – March 18, 2021, 01:42:33 pm

Quote from: bbeane – April 24, 2013, 05:59:51 am

Mine was very inaccurate, I replaced it (easy fix) 2 years ago and calibrated it per the instructions. Now it is spot on as guages go, with the coach sitting level 149 gal tank 1/2 tank =65-75 gallons. I try to fuel before the 1/4 mark, running out of fuel is a major PITA.

Billy, Do you have info on what you replaced fuel gauge with? Was it the Centroid gauge you used as a replacement or some other?

Re: Fuel gauge wonkie, really wonkie

Reply #24 – March 18, 2021, 11:28:06 pm

Our gauge was all over the place, then it only showed nearly empty. While at MOT I mentioned it to them, they replaced the whole thing and spent a good half hour calibrating it and it appears to be reasonably accurate. No needle jumping around.
Having said that after years of driving a KW, I always fill out fuel tank after a days driving, so I only get to see the top half of the gauge, (this also cuts down on getting condensation in the tank and the fuel) and makes it unlikely that we will run out of fuel.

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