What would cause this?
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Discussion

Wackywoo105

Original Poster:

493 posts

120 months

Monday 6th November 2023
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Say you get a car with a full tank of petrol and drive it over the course of a few days until it's a quarter full. You then fill it up with petrol but the petrol gauge barely moves. Slowly over the next 15-20 minutes the gauge gradually rises to full. During this time you drive the car round the block a couple of times, steering from side to side thinking maybe a sensor is stuck, but it makes no difference, so you just park up and wait?

What would cause the gauge to rise so slowly? Would opening the petrol tank to let air in/out have made any difference?

NFT

1,324 posts

52 months

Monday 6th November 2023
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Happens to mine if I only put a bit in it, takes time to register it, never when filled tank though.

Wackywoo105

Original Poster:

493 posts

120 months

Monday 6th November 2023
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The reason I ask is this happened to a rental car in Italy. I filled up at a garage just round the corner from the rental depot, where an attendant put the fuel in. The car was just under a quarter when I pulled in, 93 euros went in, around 44l. As I drove away I noticed the gauge had hardly moved. When I got the the rental depot it was just over a quarter. I told the lady working there about filling and showed her the receipt. As we watched you could see gauge was rising, but very slowly. She said she would take a copy of my receipt and make a note but then another car was returned, so she went to process it. While she did this I took if for a quick drive to see if I could speed it up. It was now about half. Thankfully we had to wait for a shuttle bus and over the next 10-15 minutes the gauge gradually rose to the full mark.

It a good job I wasn't in a rush. A similar thing also happened with a rental car in Portugal a few years back.

On another note if you ever use the Autostrada in Italy make sure you get a ticket on entering.

98elise

32,658 posts

191 months

Monday 6th November 2023
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Some just work like that. My son has a Rover 25. It takes a few minutes to register any fuel added, and the gauge moves very slowly.


Edited by 98elise on Monday 6th November 14:35

Tyrell Corp

258 posts

50 months

Monday 6th November 2023
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Fuel level gauges never read 'real time', to avoid the needle jumping around on every corner.

Old 70's cars had a thermal relay to average out the fuel level readings every few seconds, modern vehicles will have the same 'damping' feature on the guage display...although not taking 20 mins to register on full.

Could it be former owner always ran it around on less than half a tank, and the float lever switch potentiometer sticky needs some exercise - it might just fix itself after a few more tankfuls, or you just live with it.


Pica-Pica

16,621 posts

114 months

Monday 6th November 2023
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I assume it has a float with an arm and a sensor gauge on the end. Try filling it to various levels. E.g. start with a quarter, then later fill to hale, then later three quarters, then full. See what happens at each stage. The indication (or lack of) won’t affect fuel delivery. In the the meantime, use the trip odometer to ensure you don’t run out.

Wackywoo105

Original Poster:

493 posts

120 months

Monday 6th November 2023
quotequote all
This has never happened on any car I have ever owned. Like I say this was a rental car that I only had for 1 week and filled up only once. It was just an annoyance and if I hadn't been able to wait while it registered, I bet the company would have charged me, saying I hadn't filled it up.

Edit to add it was a newish (GP reg in Italy?) Nissan Qashqai.