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My Tank is Smaller Than Your Tank

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8 replies to this topic

#1
JFuller

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A bit of a strange one here.  It seems like the P38 tank level indication is not quite correct.  I noticed that when the level indicator is at the empty position the tank only takes about 16 gallons to fill before the pump shuts off and the gauge shows full again.  The manual indicates that the fuel tank holds about 24 gallons.  The other day I did a test.  The gauge was showing half full when I topped it off,  it took just over 5 gallons.  What the what?!  I don't remember this being an issue before.  Guess I have some investigation to do.  



#2
Elherbinator

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A bit of a strange one here. It seems like the P38 tank level indication is not quite correct. I noticed that when the level indicator is at the empty position the tank only takes about 16 gallons to fill before the pump shuts off and the gauge shows full again. The manual indicates that the fuel tank holds about 24 gallons. The other day I did a test. The gauge was showing half full when I topped it off, it took just over 5 gallons. What the what?! I don't remember this being an issue before. Guess I have some investigation to do.

Float on the sending unit might not float that well anymore


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#3
AdvRovr

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Agreed - sounds like a sending unit issue to me.


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#4
RedRover

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RedRover has a different but similar issue.  Ever since the gauge cluster was swapped out and a new fuel pump installed, the reading when full is pegged past the full mark and stays there until there is about a half of a tank left.

 

When the tank is close to empty, the gauge shows half-full and the dummy light is on... I'd like it to be accurate (which happens on very RARE occasion magically) but not sure what to work on first.


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#5
Elherbinator

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RedRover has a different but similar issue. Ever since the gauge cluster was swapped out and a new fuel pump installed, the reading when full is pegged past the full mark and stays there until there is about a half of a tank left.

When the tank is close to empty, the gauge shows half-full and the dummy light is on... I'd like it to be accurate (which happens on very RARE occasion magically) but not sure what to work on first.

I had a similar issue with a BMW e30 I used to own. I ended up taking the actual dial arm off the gauge and repositioning it. Not sure if that was the best way to remedy it or if that could be done with yours, but it worked for me.


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#6
DHappel

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Certainly sounds like a sender issue.  Most senders are little more than potentiates attached to floats.  It may be possible to pull out the sender and test it's action vs reading on the gauge and bend the float arm accordingly, but the real question is why you would need to do that in the first place.  Possibly a bad ground or positive at the sender causing a false reading? 

 

Not sure how hard it is to get to the sender on a P38 or how it's built.  I'm basing this on generic info.  It may well be more complicated than that (because of course it's more complicated).  

 

FWIW there are custom programmable sending units on the market but before I got into something like that I'd want to do some diagnostics on the existing part and maybe a known good one.


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#7
JFuller

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Unfortunately the sending unit on a P38 isn't quite as easily accessible as on the disco.   I was thinking float issues at first but the only way I have seen a float fail is to leak and then it sinks giving you a false low indication not a false high.  So then I was thinking about the arm being bent or misaligned but couldn't quite noodle out how it would be bent in such a way that the level would indicate full when it's actually full and trend down more quickly than it should.  I would think that if the arm was bent too far down that it would show full until the liquid level in the tank got low enough to allow the float to move.  But that's not the symptom on ours.  And it it was bent too high then it wouldn't show full enough.  The only thing I could come up with is if the arm was too long.  But how in the heck would that occur?  I will play with it a bit this weekend.  The only other thing I could think of is if the tank had a large dent in it which would be significantly reducing it's volume but I don't see that either.  



#8
Gotrovr

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Must be a LR thing.  I'm having the same issue with my MY16 LR4


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#9
Elherbinator

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Unfortunately the sending unit on a P38 isn't quite as easily accessible as on the disco. I was thinking float issues at first but the only way I have seen a float fail is to leak and then it sinks giving you a false low indication not a false high. So then I was thinking about the arm being bent or misaligned but couldn't quite noodle out how it would be bent in such a way that the level would indicate full when it's actually full and trend down more quickly than it should. I would think that if the arm was bent too far down that it would show full until the liquid level in the tank got low enough to allow the float to move. But that's not the symptom on ours. And it it was bent too high then it wouldn't show full enough. The only thing I could come up with is if the arm was too long. But how in the heck would that occur? I will play with it a bit this weekend. The only other thing I could think of is if the tank had a large dent in it which would be significantly reducing it's volume but I don't see that either.

You're getting false high readings? The original post indicated it was reading lower than it should. Like the float was sitting lower than it should. Often the floats have a seam in the middle of it that fails. It will allow it to fill up, but usually not completely. An air pocket above the seam failure will still exist allowing it to still float, just lower. If I had to guess at the issue, I'd go with that. You'll probably just have to pull the fuel pump to see. At that point, might as well just swap in a new one


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