Fuel tank

[Jackrabbit83]

Hello all… I’m kind of confused and very new to the skoolie world. We have a 28’ flat nose blue bird… 5.9 liter diesel Cummins engine… the fuel hatch has a label on the door stating it is a 60 gallon diesel fuel tank… but when I fill the tank when the “low fuel” light comes on, I can only put 30 gallons in… am I missing something? Is there a second tank I don’t know about? Scratching my head not quite understanding. Help!!!

Tia!!

Abed and Chelsea

[fo4imtippin]

There is probably an issue with the fuel gauge. I have a 28ft TC2000 and it has a 60 gallon tank. If it's behind the rear axle, then I'm sure that's what you've got. Older TC2000 have 40 gal tanks on passenger side between the axles.


There should be an access hole in the floor of the bus above the tank. You might need a new sensor.


Btw, I wouldn't ever let your tank go below 1/4 of fuel( don't wait for warning on dash) because you will suck dirt through the filters and plug them. Unless you have dropped and cleaned your tank, this is my advice.

[Jackrabbit83]

Originally Posted by fo4imtippin

There is probably an issue with the fuel gauge. I have a 28ft TC2000 and it has a 60 gallon tank. If it's behind the rear axle, then I'm sure that's what you've got. Older TC2000 have 40 gal tanks on passenger side between the axles.


There should be an access hole in the floor of the bus above the tank. You might need a new sensor.


Btw, I wouldn't ever let your tank go below 1/4 of fuel( don't wait for warning on dash) because you will suck dirt through the filters and plug them. Unless you have dropped and cleaned your tank, this is my advice.

Thank you for the reply. So you think it might be a gauge issue, but I was only able to fill with 30 gallons though… I will need to do some research on the sensor. In the middle to angle grinding rust and I’m literally sitting on the hole in the floor. Our fuel tank is in between the front and rear axles.

[fo4imtippin]

It could be 40 gallons as the side frame mount ones came that small. Never heard of 30 gallons. I would go measure the tank from below and calculate LxWxH for gallons. Below is a diagram for a side mount, so you can account for the brackets.

[HamSkoolie]

Originally Posted by fo4imtippin

Btw, I wouldn't ever let your tank go below 1/4 of fuel( don't wait for warning on dash) because you will suck dirt through the filters and plug them. Unless you have dropped and cleaned your tank, this is my advice.

Not sure where this dirt would be coming from. The tank is sealed. The entire fuel system is sealed except when you're pumping in fuel. You won't get dirt in the fuel unless you're fueling from something like a farm tank on a stand with a dirty nozzle.
And the purpose of the filters.....it's to remove any contaminant that does get into the system.
Never run out of fuel but to refuel at 1/4 tank isn't required.
NOW if you want to discuss being prepared....for that unexpected emergency situation....never let the fuel go below 1/2 so that you can get away from a natural disaster, riots, whatever.

[Spaznaut]

Harder for pumps to pull from 1/4 full tank. Most of that comes from vehicles with the pump in the tank and the submersion helps keep the pump cool. After 10+ years you can get some debris in the tank especially if if has sat quite a bit and moisture was allowed to rust it on the inside. Your best bet is going to be to run it until the light comes on and then look in the tank and see where the fuel level is sitting. Some of those sending units have filters in the tank that may need to be checked and changed (or removed in some cases if an external filter is added or present).

[magnakansas]

I think my tank is around 30 to 35 gallons. My bus is only 25 feet long. I get between 10.5 and 12.5 miles to the gallon. I have the cummins 5.9 with bosch p7100 injection pump. and the 545 transmission. 4.78 rear gear ratio.

I base my 30 to 35 gallon figure on what the fuel gage reads, and how much I have filled it. I have not measured the tank to calculate volume.

I want to replace the side saddle tank with a 100 gallon tank that will sit between the frame rails behind the rear axle.

william

[Rivetboy]

Originally Posted by Jackrabbit83

Hello all… I’m kind of confused and very new to the skoolie world. We have a 28’ flat nose blue bird… 5.9 liter diesel Cummins engine… the fuel hatch has a label on the door stating it is a 60 gallon diesel fuel tank… but when I fill the tank when the “low fuel” light comes on, I can only put 30 gallons in… am I missing something? Is there a second tank I don’t know about? Scratching my head not quite understanding. Help!!!

Tia!!

Abed and Chelsea

Hi, Joe here. I have a 1991 28 foot TC 2000 with a 5.9 and a 545. My tank was mounted on the passenger side and measures out to 52 " long 20 " wide and 14 ". tall That multiplies out to 14520 Cubic inches. Divided by 231 Cubic inches (1 gallon) equals out to 63 gallons . So fudge my measurement a bit and I believe I have a 65 gallon tank.

[Booyah45828]

I don't run anything of mine below 1/4 tank. Several reasons for that. One is because sending units can be inaccurate. Once you know how senders/floats operate, you realize the 1/4 number could possibly be no more then a guess, especially on older vehicles. Two is because in-tank mounted fuel pumps rely upon submersion to keep cool. No submersion, no cooling, and cooling is paramount for longevity. Three has to do with steel tanks and how running below 1/4 exposes more metal for condensation, and I'd rather not have that.

And finally, what do you gain by it? Time not spent filling fuel? That's a moot point with how much time we waste on other things, but I digress.

FWIW, tanks are not sealed, they vent to the atmosphere for temp/pressure changes and what not. Gas vehicles with explosive vapors will use a charcoal canister to do so, diesels might just vent it to the filler neck and cap, some just vent to a hose pointed at the ground. But they all vent regardless.

[Booyah45828]

Originally Posted by Rivetboy

Hi, Joe here. I have a 1991 28 foot TC 2000 with a 5.9 and a 545. My tank was mounted on the passenger side and measures out to 52 " long 20 " wide and 14 ". tall That multiplies out to 14520 Cubic inches. Divided by 231 Cubic inches (1 gallon) equals out to 63 gallons . So fudge my measurement a bit and I believe I have a 65 gallon tank.

No, the tanks volume is a rated number and not measured number. There's always an air gap at the top that can be as much as 10%, so unless your numbers are way fudged, you likely have a 60 gallon tank, which was pretty common for that vintage bluebird.

[HamSkoolie]

Originally Posted by Booyah45828

I don't run anything of mine below 1/4 tank. Several reasons for that. One is because sending units can be inaccurate. Once you know how senders/floats operate, you realize the 1/4 number could possibly be no more then a guess, especially on older vehicles.

All true and all very good reasons to run your rig to complete empty when you first get it. Bring a 5 gallon can (or two of them) with you and stay relatively close to fueling stations. Run it until you feel the first sputterings making note of the mileage when the low fuel light comes on.
Pull over
Note the location of the fuel gauge needle
Note the mileage
Pour in the can(s) of fuel
Proceed directly to the fuel station
At the fuel station note the mileage and fill the tank as full as you can get it.
Use your mileage notes to determine how far after the low fuel light you can push it and to calculate fuel consumption between the place you ran out of fuel and the fuel station thus being able to calculate how large the actual capacity of your tank is.
NOW you have all teh information you need to avoid running our of fuel as well as to avoid unnecessary fuel stops.
I have done this since the very first car I bought as an 18 y/o Marine. I ran out of fuel at 1/4 tank because I never even considered the gauge might be wrong. On my F350 real empty is two needle widths below the E and takes 20 miles after the E to get there.

Originally Posted by Booyah45828

Two is because in-tank mounted fuel pumps rely upon submersion to keep cool. No submersion, no cooling, and cooling is paramount for longevity.

Except that the system and components are designed to allow use of the entire fuel volume. In all my years as a mechanic I've replaced two in tank fuel pumps. They can indeed fail just like any other part but it's not likely because of cooling from running under 1/4 tank.

Originally Posted by Booyah45828

Three has to do with steel tanks and how running below 1/4 exposes more metal for condensation, and I'd rather not have that.

This is a legitimate concern. Particularly if one routinely leaves at tank at low levels. Not really a problem with gasoline vehicles any more as the alcohol in today's gasoline absorbs moisture and pulls that condensation through the motor along with the crappy alcohol and the actual gasoline.

Originally Posted by Booyah45828

And finally, what do you gain by it? Time not spent filling fuel? That's a moot point with how much time we waste on other things, but I digress.

It depends on what you're doing. On a 10,000 mile trip on a short schedule refueling at 1/4 or higher rather than 1/16 tank or lower means quite a few extra stops (21% more stops). Each extra stop increases time for the trip as well as risk incurred to people and equipment. Here's some numbers for an imaginary trip using our current pickup and 5th wheel tankage and economy.



10,000 miles at 12 mpg 833 gallons 40 gallon tank
fuel @ 1/16 tank (2.5gal/30 miles reserve) = 450 miles/tank = 22 stops

fuel @ 1/8 tank (5gal/60 mile reserve) = 420 miles/tank = 24 stops
fuel @ 1/4 tank (10gal/120 mile reserve) = 360 miles/tank = 28 stops


And here is a trip we actually made, from Oregon to Pennsylvania, down to Georgia, then to New Orleans, north to Wyoming, and then back to Oregon. 23% more fuel stops, in unfamiliar territory, with unfamiliar risks, just by refueling early. And I do push the distance between fuel stops on long trips..... and carry 5 gallons in one of the utility bays on the pickup just in case I screw up.



7,800 miles at 12 mpg 650 gallons 40 gallon tank
fuel @ 1/16 tank (2.5gal/30 miles reserve) = 450 miles/tank = 17 stops

fuel @ 1/8 tank (5gal/60 mile reserve) = 420 miles/tank = 19 stops
fuel @ 1/4 tank (10gal/120 mile reserve) = 360 miles/tank = 22 stops

Originally Posted by Booyah45828

FWIW, tanks are not sealed, they vent to the atmosphere for temp/pressure changes and what not. Gas vehicles with explosive vapors will use a charcoal canister to do so, diesels might just vent it to the filler neck and cap, some just vent to a hose pointed at the ground. But they all vent regardless.

In the old days all vehicle tanks vented to the ambient atmospheric pressure. Today's "environmental" rules don't allow that for gasoline tanks. In fact, if you don't have positive pressure on your gasoline fueled vehicles tank, it will throw a code (P0455) for a "gross evaporative emissions system leak". They will vent to the atmosphere at dangerous pressure levels but the norm is that they do not. By raising the pressure in the tank the evaporation point of the gasoline.

While diesel doesn't evaporate as easily as gasoline and so can be vented to the atmosphere the systems are still sealed against outside contaminants through the use of filters that prevent contamination from entering through vents.
There is also a misconception, largely due to hollywood explosives experts, that the fuel vapors in a gas tank are explosive. This is PATENTLY FALSE. While gasoline vapors can explode, they can only do so when between the upper and lower explosive levels.....the right fuel air mixture for the lay person. Crashing off a cliff, a fire in the filler neck, or even directly under a fuel tank WILL NOT CAUSE AN EXPLOSION. There can be a ruptured tank and a gasoline fueled fire but not an explosion.
Three of the things I used to demonstrate in safety classes (under controlled conditions with proper safety equipment and emergency equipment) was that indeed, you can put out a match in gasoline, that only gasoline vapors burn, and that there must be the right fuel/air mixture for it to burn. Too rich or too lean and there will be no combustion let alone explosion.


Explosions are fun and an expert can make gasoline explode, but car fuel tanks don't (unless an expert is having some fun and creates the perfect conditions)


IYAOYAS

[Booyah45828]

Originally Posted by HamSkoolie

Run it until you feel the first sputterings making note of the mileage when the low fuel light comes on.

Please don't do this on any vehicle, even more so a diesel vehicle, even more so a bus/semi/straight truck. Some of those take forever to get the fuel system to bleed the air, and some of them require significant cranking to do so as well. A lot of them rely upon fuel pressure and volume to keep the injection pump cooled and happy as well.

Running it out or near out isn't smart or necessary. What's it matter if you leave 1/4 tank and fill up? Nothing. Just fill the thing up at 1/4 tank and be done. There's no need to get every last ounce out of the thing before filling up.

Originally Posted by HamSkoolie

Except that the system and components are designed to allow use of the entire fuel volume. In all my years as a mechanic I've replaced two in tank fuel pumps. They can indeed fail just like any other part but it's not likely because of cooling from running under 1/4 tank.

No they're not. This isn't propane, they're not designed to run on fumes, and they don't do it well when you force them to either. If you must run it low, do it, but don't make a habit of it, as longevity suffers. I've seen it first hand in the pumps I've replaced. I find your mechanic experience odd, as I've replaced hundreds of in-tank pumps in the 15+ years I've been doing this. I'm pretty sure my recommendation of filling at a 1/4 is backed by most pump manufacturers as well, at least their reps have all agreed with me on it. Cooling an in-tank pump is done solely by it being submerged in the fuel. Occasionally the fuel return will dump back into the sending unit on top of the pump to keep it wet. Also, a lot of your sending units actually have a cavity in them to hold fuel around the pump and to keep it cool as well. Keeping the pump cool is vital to it. It's an electric motor, and longevity suffers when electric motors are ran hot.

Originally Posted by HamSkoolie

It depends on what you're doing. On a 10,000 mile trip on a short schedule refueling at 1/4 or higher rather than 1/16 tank or lower means quite a few extra stops (21% more stops). Each extra stop increases time for the trip as well as risk incurred to people and equipment. Here's some numbers for an imaginary trip using our current pickup and 5th wheel tankage and economy.



10,000 miles at 12 mpg 833 gallons 40 gallon tank
fuel @ 1/16 tank (2.5gal/30 miles reserve) = 450 miles/tank = 22 stops

fuel @ 1/8 tank (5gal/60 mile reserve) = 420 miles/tank = 24 stops
fuel @ 1/4 tank (10gal/120 mile reserve) = 360 miles/tank = 28 stops


And here is a trip we actually made, from Oregon to Pennsylvania, down to Georgia, then to New Orleans, north to Wyoming, and then back to Oregon. 23% more fuel stops, in unfamiliar territory, with unfamiliar risks, just by refueling early. And I do push the distance between fuel stops on long trips..... and carry 5 gallons in one of the utility bays on the pickup just in case I screw up.



7,800 miles at 12 mpg 650 gallons 40 gallon tank
fuel @ 1/16 tank (2.5gal/30 miles reserve) = 450 miles/tank = 17 stops
fuel @ 1/8 tank (5gal/60 mile reserve) = 420 miles/tank = 19 stops
fuel @ 1/4 tank (10gal/120 mile reserve) = 360 miles/tank = 22 stops

7800 miles traveled at an avg of 60 mph is 130 hours. It takes what, at most 5-10 minutes to fill up a 40 gallon tank and be back on the road? So you saved half an hour? That's less then 1% of your total trip time. And that's if you're driving the 130 hours non-stop. I'd love to meet the superhuman that can do that.

>99% of the population will stop several times on a roadtrip. Stop to grab food, stop to take a leak, stop to see something cool, stop to walk around, etc. Whatever you're stopping for, it makes sense to fill up while you're stopping, then to go another 20 minutes and stop again for fuel only.

The 1% that don't stop on a roadtrip are the indian trios stuffed into a volvo sleeper with a hole in the floor and 100+ gallon saddle tanks that run round the clock making coast to coast runs. But with that much fuel onboard, they're not stopping for fuel on the trip anyways.

FWIW, if you get in a desolate stretch out west in Arizona, Wyoming or Montana you won't have a choice between 1/4+ and a 1/16 tank because the fuel stations aren't that close together.

Originally Posted by HamSkoolie

In the old days all vehicle tanks vented to the ambient atmospheric pressure. Today's "environmental" rules don't allow that for gasoline tanks. In fact, if you don't have positive pressure on your gasoline fueled vehicles tank, it will throw a code (P0455) for a "gross evaporative emissions system leak". They will vent to the atmosphere at dangerous pressure levels but the norm is that they do not. By raising the pressure in the tank the evaporation point of the gasoline.

That is NOT how it works. In gasoline vehicles the top of the tank is connected to the evap canister and it's what captures the fumes. With the key off, the canister and tank are venting to the atmosphere, and any fumes created are caught by the carbon in the canister. Key on, and the tank is either purging the vapors from the carbon into the running engine, venting any pressure in the tank to the atmosphere, or it's sealed and under vacuum to check for leaks in the system. Your gas tank should never be under pressure. If it is, something is faulty in the system. The whoosh you might hear when removing the cap to fill up is actually from vacuum in the tank, not pressure.

The old days they did vent to the atmosphere, but that's going back 50+ years, as the epa started controlling that in the late 60's. Fuel vapors are a major contributor to smog in CA and other urban areas. You can put environmental in quotes all you want, but nobody in their right mind would go back to the smog of the 60's. FWIW, I don't agree 100% with the EPA, but some things they have gotten right over the years.

Originally Posted by HamSkoolie

While diesel doesn't evaporate as easily as gasoline and so can be vented to the atmosphere the systems are still sealed against outside contaminants through the use of filters that prevent contamination from entering through vents.

What diesels are you talking? Passenger vehicles it's a possibility, but a lot of your md and hd diesels still use a simple hose with a rollover valve on the tank(s). Some might have a small filter on the end, but it's more of a screen then a filter. You'll actually see a lot of them cut off, as it's cheaper to do that when the screen is plugged then it is to replace them, and those screens don't filter that well anyways, they just plug up and cause problems.

[HamSkoolie]

Well as someone who's

1) first automotive maintenance lessons began in the 1960's... AND

2) the top graduate of a two year formal civilian technical school automotive course covering everything from day one "this is a screwdriver" (arrrrrgh) to tear down and rebuilding of engines and transmissions... AND
3) the former Maintenance Management Officer of MROPCTU, MCLB Barstow... AND
4) the former Maintenance Management Officer of Marine Wing Support Squadron in Alameda... AND
5) former county transit department mechanic... AND
6) former ASE certified mechanic
I'll stand by my statements.

Also, whether a tank is positively or negatively pressurized, it is indeed pressurized unless there is a total vacuum. Atmospheric pressure, standard day, at sea level, is 14.7PSI. 12PSI may be perceived as a vacuum but it is indeed 12PSI of PRESSURE. Only a vacuum isn't pressure.
As for LA smog.... that's a product of stacking people up like cord wood in an area unsuitable to support that much human habitation.

[TheHubbardBus]

Originally Posted by HamSkoolie

And here is a trip we actually made, from Oregon to Pennsylvania, down to Georgia, then to New Orleans, north to Wyoming, and then back to Oregon. 23% more fuel stops, in unfamiliar territory, with unfamiliar risks, just by refueling early. And I do push the distance between fuel stops on long trips..... and carry 5 gallons in one of the utility bays on the pickup just in case I screw up.

7,800 miles at 12 mpg 650 gallons 40 gallon tank
fuel @ 1/16 tank (2.5gal/30 miles reserve) = 450 miles/tank = 17 stops

fuel @ 1/8 tank (5gal/60 mile reserve) = 420 miles/tank = 19 stops
fuel @ 1/4 tank (10gal/120 mile reserve) = 360 miles/tank = 22 stops

I can't agree that pushing the limits like this increases security. If you view fuel stops as unfamiliar risks in unfamiliar territory, what's a better bet: Having the fuel available to pick and choose where/when you stop, or pulling into the only mad-max-themed stop-n-rob w/in a 200-mile radius after the low-fuel indicator's been glowing for half an hour and you have no other choice? Stopping early & often gives you options. Waiting till the last moment to fill up takes them away. What happens when the pumps are down? What if diesel never got delivered? Yeah, you've got 5 gallons. But that won't get you far. And if a well-lighted public fuel stop is a security risk, I'd think filling up your bus on the side of the road in the dark from a jerry can orders of magnitude more hazardous.

You do you, but I'll take early & often any day of the week. Mechanical questions aside, it's simply far less stress. The whole purpose of the bus for us is to slow down and enjoy the journey. Unfamiliar territory is pretty much the point (to a point)

[cadillackid]

Originally Posted by Rivetboy

Hi, Joe here. I have a 1991 28 foot TC 2000 with a 5.9 and a 545. My tank was mounted on the passenger side and measures out to 52 " long 20 " wide and 14 ". tall That multiplies out to 14520 Cubic inches. Divided by 231 Cubic inches (1 gallon) equals out to 63 gallons . So fudge my measurement a bit and I believe I have a 65 gallon tank.

60 gallon is likely what it was sold as.. im guessing they give a little less in capacity than the measured cubic inches is due to the fact you lose a few inches at the top as most school busses have no true filler neck so you arent gilling the tank 100% to the ceiling.. thus making it sold as a 60 gallon tank..

[Jackrabbit83]

There is a lot of information here… thank you! Still scratching my head though. Fuel gauge reads full, I run it to damn near empty. I can literally only fill it with 30-35 gallons. The needle says empty and the light comes on. The sticker on the side reads “equipped with a 60 gal fuel tank” maybe they meant 35 gal fuel tank?! ��*♂️

[Mercuric Mind]

Is there a drain plug on the tank? You could drain, catch, and measure the volume of remaining fuel just after the gauge reads empty or 1/4. Then you would know for sure how much is in there. IDK If this would cause any issues with the fuel system in general, it is just a suggestion.

[Booyah45828]

Originally Posted by HamSkoolie

Well as someone who's

1) first automotive maintenance lessons began in the 1960's... AND

2) the top graduate of a two year formal civilian technical school automotive course covering everything from day one "this is a screwdriver" (arrrrrgh) to tear down and rebuilding of engines and transmissions... AND
3) the former Maintenance Management Officer of MROPCTU, MCLB Barstow... AND
4) the former Maintenance Management Officer of Marine Wing Support Squadron in Alameda... AND
5) former county transit department mechanic... AND
6) former ASE certified mechanic
I'll stand by my statements.

Congrats I guess? None of that disproves or disputes anything I said. You've got an opinion and had a career, Great Job!

Originally Posted by HamSkoolie

Also, whether a tank is positively or negatively pressurized, it is indeed pressurized unless there is a total vacuum. Atmospheric pressure, standard day, at sea level, is 14.7PSI. 12PSI may be perceived as a vacuum but it is indeed 12PSI of PRESSURE. Only a vacuum isn't pressure.

Cool play on words. Absolute pressure, no such thing as vacuum, we can go round and round all day long with that. By that theory, there's no such thing as negative pressure, because you can't get less then 0 absolute pressure, right? Or has the galaxy changed since I've been in school?

When I took the ASE tests 10+ years ago they didn't refer to evap as pressure, it was always vacuum, because it's under vacuum compared to the atmosphere around it. My certs have since expired, because they weren't valuable to me. Not one customer asked about them while I had them, not one verified that I had them, and this is the only time I've mentioned them since their expiration. Some can value them, I honestly don't. The tests aren't hard, and don't really demonstrate your ability at fixing anything.

Rereading your post, I don't see how one could misread this statement

Originally Posted by HamSkoolie

In fact, if you don't have positive pressure on your gasoline fueled vehicles tank, it will throw a code (P0455) for a "gross evaporative emissions system leak". They will vent to the atmosphere at dangerous pressure levels but the norm is that they do not. By raising the pressure in the tank the evaporation point of the gasoline.

as it not being at a pressure greater then that of atmosphere. Which is wrong. It's either at or less then atmospheric pressure. Being less then atmospheric pressure, a large majority of the planet would consider under that to be under a vacuum.

Flaunt your accolades, trash mine, I don't care. You posted wrong info, there's no other way around it.

[Booyah45828]

Originally Posted by Jackrabbit83

There is a lot of information here… thank you! Still scratching my head though. Fuel gauge reads full, I run it to damn near empty. I can literally only fill it with 30-35 gallons. The needle says empty and the light comes on. The sticker on the side reads “equipped with a 60 gal fuel tank” maybe they meant 35 gal fuel tank?! ��*♂️

Sorry, most of it is rants by me. I apologize.

Fuel tanks can be replaced if they're rusted and unsafe. That sticker might be wrong. You can use a tape measure to get the rough dimensions and calculate your volume. Not to speak bluntly or make you feel dumb, but do the math and you'll know pretty quick if your tank volume is around 35 or around 60, as the 60 would be double the size compared to a 30.

Just recently we replaced a 100 gallon tank with a 40 gallon unit, because it was less then 1/3 the cost. The bus is a spare and doesn't leave the county, so 40 gallon should be plenty. It will very likely be retired soon, so we're saving as much money as we can with it.

Like I said in a prior post, fuel gauges aren't necessarily guaranteed accurate. It could read E and the light could be on but still be half full, or they can read half full and be bone dry. The float arm could be bent, you could have resistance in one of the connections, the float itself could be fuel logged, there are a lot of fault points. Measure the tank and we'll go from there.

[cadillackid]

Another thing you can do is if you have an access plate inside the bus on the floor above the tank . Pull it and pull out the sending unit and stake the tank. If the gauge reads 1/4 and you have half tank fuel you can figure something is wrong with the gauging system.

Depending on the vehicle , the sender may expect to get its ground from the tank. This almost always begins to fail at some point as the vehicle ages. Using a clip wire from the ring of the sender to a good bare part of the bus frame will temporarily fix that for testing..

I have seen the dash gauge die but far more likely is a failing sender unit. The float moving does nothing more than operate a variable resistor that often gets dirty over the years. This causes poor contact of the float wiper and errant readings..

I’ve had to replace the sender unit in both my IH diesels and one is starting to act wonky again (6years later)..

I’ll never cover the sender access plate up with equipment or new floor in any of my busses