HI,
I recently purchased a lovely Mondeo with 98k mls and fresh belts n w-pump and car test.
She was just under half full so i decided to fill her right up (ca 40liters) to see what the range is.
Nicely showing 1285 km estimated (of course if you drive max efficient, tail wind etc) on full tank and fuel gauge at max.
Drove shopping etc all is fine.
Last night we had some freezing temps ca -2 or -3 and when i started the car this morning she was showing 3/4 full only.
I drove a few kilometers and decided to pullover to switch off and restart car so it might fix itself and gauge went down to half full only.
I carried on another 10min and stopped again to have a look if i got a leak but all seems dry nothing dripping etc.
I then went on a drive for about 120km gentle and calm and now she is at just under a quarter tank on gauge.
She should be  between 3/4 and full.
So this must be electronic issue, searching for it doesn't get many results for my car year and type.
Anyone any ideas or similar issues experienced? Thank you!

Update:
Talking to the dealer tomorrow, bit late now and emailed dealer to save me telling my whole experience again.
I broke down and not even done 300km yet, below is the email i sent to the dealer in advance of my phone call, read on if you wish to share my experience:

 

Hi XYZ,
I will call you tomorrow, the car broke down, not even done 300km yet.
Here is summary last few days:
Saturday - got the car all seems very well, sometimes a rattle at idle, not sure if flywheel but I guess could be the drive shaft as it has a good bit of play.
She was 1/2 full on diesel so decided to fill her up max ca 35l and she nicely shows full, 1280km range max.
Sunday I had to drive my wife to chemo in Cork and when starting the car got a battery warning but she started fine and the tank now shows 3/4.
So i took off (Cork is 64km from here so ca 130km round trip) but decided to pull over and switch off the car to see if the fuel gauge pops back to max but instead shows 1/2 full only now.
So I popped the bonnet to see if she was leaking and looked underneath, all clear.
Drove there and back all good, besides this rattle from the low engine area occasionally.
Monday I just checked the car, got a battery warning (it's cold right now again) but she started fine and showed 3/4 full, as expected, so I just let her warm up and switched off.
Today I had to drive my wife to Cork again,  and she showed almost empty, knowing that she is at least 3/4 full as I only did like 150km max and she showed it's fuel gauge fine 2 days ago. I ignored the fuel gauge.
Drove to Cork fine, on the way back error came up " Engine Malfunction " and she went into low power 1sec, bit more power 1sec, back and forth. So I pulled over and she cut out. I got a friend to tow me to his place, She still shows the above error and looks like not getting diesel, not sure without error codes.

So there you have it, let's talk tomorrow about how we can solve this, i need a drink now.

Kindly,
Stefan

I had the same fault on my Mk4, I took it to a garage who diagnosed the float as faulty, I had a new pump / float chamber fitted problem solved. It was something to do with the float electrics on the pump side.

On 4/9/2021 at 10:48 AM, 007 Mondeo said:

I had the same fault on my Mk4, I took it to a garage who diagnosed the float as faulty, I had a new pump / float chamber fitted problem solved. It was something to do with the float electrics on the pump side.

Thanks, got my float unit replaced and car back today too, so far so good. She is a sweet ride and i finally can enjoy her.
I also done full service & all filters, new battery, drive shaft had play so replaced that and drive shaft bearing was knackered too.
Super happy now and peace of mind finally. 😇🥰