I bought my Clio at the beginning of the year and honestly the fuel consumption seems off to me. I'm mostly doing city and semi-urban driving, and I'm getting around 8.5L/100km when the manufacturer claims 5.5. I haven't had any accidents, the engine runs normally, no warning lights are on. Maybe it's an engine tuning issue or a clogged filter?
A 3L/100km difference is pretty significant, so before you start panicking you need to check the basics. Are your tires properly inflated? You won't notice an underinflated tire while driving but it eats up fuel for nothing. Also, the way you drive has a huge impact in the city - if you accelerate hard then brake, if you idle too long, it absolutely tanks your consumption. Since you bought your Clio have you changed your routes or your driving habits? These are dumb questions but that's usually where it comes down to.
If it's really a mechanical issue, I'd start with the air filter (a lot of people forget about it), then the spark plugs if they're old. A spark plug that's acting up might not feel dramatic when you're driving, but it changes everything fuel-wise. Are your brakes dragging? Sometimes a caliper that's sticking a little, you barely feel it but that friction is just fuel going up in smoke.
Where people generally don't think to look is the fuel itself - are you switching gas stations? Some low-quality stations sell less energetic fuel or fuel with water in it. It's rare but it happens. Try filling up at a good station (Total, Shell, etc) and do a proper test over 200-300 km before you freak out. And one more dumb thing: are you sure your fuel gauge isn't messing with you? Like it's not rising too high or it's fluctuating? Gauges acting up is more common than you'd think on new cars.
Manufacturer figures are calculated in the lab under pretty much perfect conditions, so you should already expect some difference there. Like 8.5 versus 5.5 is pretty steep, but it's not necessarily abnormal especially if you're doing a lot of city driving. In town you've got tons of acceleration and braking, traffic jams, the engine idling... all that uses way more fuel than cruising on the highway. You've also got to look at how you're actually driving: are you doing hard takeoffs, letting the engine run before you take off, keeping the revs high? Tire pressure is huge too, so check it when they're cold first.
On the air filter, yeah it's possible but honestly a 2024 Clio should still be under warranty normally, so the filter should be fine. Look more at the coolant and engine oil instead, because an engine that's not running at optimal temperature uses more fuel. After that if you really want to get to the bottom of it, get a diagnostic done at a Renault dealership: they'll scan it properly, check the sensors, see if there's something weird going on with the engine adaptation or an injection problem. It might cost you a hundred bucks or so but you'll have your answer instead of going in circles, and it's still covered by warranty anyway.
Before you torture yourself with mechanics, just take a look at your driving style in the city - lots of accelerations and braking literally kill fuel consumption! And then check that you're filling up the tank the same way each time, because a bad measurement at the start messes up your whole calculation.
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