I recently bought a 97 F350, and I'm not sure if the fuel gauge is malfunctioning or I just dont understand how it works.

Is it suppose to show the level of both tanks combined, or just the selected tank?

With the fuel gauge at empty (for either tank selected) I put 15 gallons in the front tank and put 5 gallons in the rear, which made the gauge read at half. After about 70 miles it was back down to empty which freaked me out since I thought I was getting the worst mpg possible. When I went to fill it up again, i could only get about 4 gallons in the front. So I also filled the rear tank up, which made the gauge read full again. On the front tank I've driven just over 300 miles and its back down to empty again (havn't used the fuel in the rear tank yet), so I have absolutely no idea how much fuel I have left since I dont understand this gauge. Really feels like its broken somehow.

Any insight to this?

 

gage shows fuel amount for front tank only when switch is on front tank and shows for the rear when you switch it to the rear yor 4 gallons in 70 miles is 17.5 mpg is avg i thing you have a problem with the switch or the valve

 

Welcome to

The gauge only reads the selected tank. The rear tank holds 18.2 gallons. The front tank holds 19 gallons. Subtract about 0.5 - 1 gallon and that's close to your usable amount of fuel.

I consistently use 17.4 - 17.6 gallons from the rear tank when I fill up. I've run the front tank down a few times and used about 18.4 - 18.6 gallons when I filled up.

Sounds like your float (fuel level sensor) is faulty and needs replacing. Unfortunately, you can't replace the float by itself. You'll need the entire assembly.

Until you fix this, I suggest you pay attention to how many miles you're driving. It's generally considered a no-no to run a diesel dry, but...

I've done this to get an idea of how many miles I can drive when using the rear (little) tank. Fill both tanks full so you're sure they're full. Switch to the rear tank and do your normal driving. Monitor the odometer as you get close to "empty". You'll feel the engine get really "angry" with you for not feeding her. SWITCH TANKS NOW! Hopefully, you'll be on the freeway to have some speed to help you. Keep your foot on the go pedal and ride it out. You'll know when fuel is reaching the engine. Notice how many miles you drove before you ran out of fuel. Take your truck to the filling station, preferably the one you regularly use and use the same pump. (I set the nozzle far enough inside the fuel inlet pipe to keep the fuel flowing and set on the first notch for a nice, slow fill.)

Do the same thing with the front tank. That will give you a good "guesstimate" on far you can drive before switching tanks. If you do this consistently, (run on the rear tank and switch to the front tank), you'll have an idea of how far you can go on both tanks.

For example: I run the rear tank and travel about 290 miles. I switch to the front tank. I run another 290 miles (odometer total of 580 miles) and am looking for the next filling station.

Does that help?

 

Thanks for the info. The sensors being broken/misreading sounds about right with how it's behaving. I'll probably just try to go off mpg like you suggest since this truck is just going to be my weekend warrior for heading up the mountains to go skiing or snowmobiling. I'm sure I'll evetuntually get around to fixing it though

 

Glad we could help.

As a new member, you may or may not know about the "Scales" in the upper-right corner of the post. That's used to add reputation points to individuals who've helped you out with a bad situation.

Keep that in mind for your future questions.

If you're just using the truck on the weekends for trips to the mountains, fill up both tanks before you go and have a great time.

Look forward to more of your questions. You'll gain a lot of good info here. These guys are great.

 

Had a new development with this. I havn't really driven the truck since I last posted this, but I decided to drive it to the store today and switched it over to the rear tank which should be full from my last fill up. The needle didnt move (still in E from the front tank which should have little fuel after going about 320 miles on it), so figured the rear tank has a bad float and is just not reading. I made it about 4 miles and ran completely out of fuel
Since it was 11pm and I was blocking a lane, I called a tow truck/shop about 5 blocks away to pick it up and check it out tomorrow. He's going to figure out what is going on with the fuel system also so I'm not just guessing.
Sucks I have to pay for a tow and repair, but I just want to get this solved now cause I don't trust it at all.

 

Better safe than sorry. 320 miles on the front tank? What gears are you running? Must be 3.73:1, right?

Good luck with this. Let us know what it turns out to be. If the shop is pulling the tanks, have them reseal the insides (if that's still done). I had that done with my '64 Fairlane 500 Sports Coupe. I could use nearly the full 20 gallons in the tank after having it resealed.

Not sure if "resealed" is the correct term either. They basically added a coating to the inside of the tank that flowed into all the nooks and crannies left over from the manufacturing processes of the '60s.

 

No joke. My truck has the 4.10 rears and I only get about 150-180 miles per tank.

 

Well mystery solved. It has been running on the rear tank since it was bone dry, which makes alot of sense now. They pumped 5 gallons from front tank to the rear, bleed the line, and she fired right up. I guess the fuel tank switch is not working, hopefully its a simple fix?
Least I know what is going on now though, and the fuel gauge itself is actually working I was just assuming the switch was working.

 

the switch may be working.....the valve may not be.....with the motor off and key on...have someone flip the switch while you listen.....the valve will be on the frame rail under the back of the cab...it will sound like a elec fuel pump.....there are pics of it around here somewhere....I will look for them

 

since you gauge changes I know it is that valve.....it also switches the sig for your gauge.Still looking for pics

 

Actually the guage does not change when I flip the switch. It stays reading the rear tank only.
Thanks for your help.

 

1st Check fuse #6 under the dash. It protects the fuel selector, AC clutch and RKE (Remote Keyless Entry)

If the fuse is OK then:

It could be the switch in the cab or the fuel tank selector valve on the frame rail.
If you are handy with a volt/ohm meter to should be able to track it down. You
can check everything at the connector on the valve.


Here's the schematic: Notice you can check you fuel gauge sender(s) too if you
know how much fuel is in the tank(s). 145 Ohms full and 22.5 Ohms empty.

Let us know how it turns out for you.
BTW: Welcome to FTE





You'll find the selector valve under the driver seat on the inside of the frame rail.
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Here's the connector pin out:
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real good info jim.
reps sent.
my fuel gage for the front tank reads eratic sometimes (way too full) and i can use this info.

 

Wow, thanks for that Jim. Should be very usefull for me to track it down with that now! I'll let you know how it turns out.