New Car Fuel Usage & OBD2 Scanner

Hey All!

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BackStory:

I don't know much about cars but I think I do decent enough research - I recently bought a 2006 Mitsubishi Outlander from the advice of a good family friend - it was 50% lower than current market value with seemingly the only issue is the clear coat peeling beyond repair - It's got 155k kms done on it and all minor and major service history checks out, One problem though is it guzzles fuel like no tomorrow - My napkin math checks it in at 14-18L Per 100km, I do 90% highway driving since on and off ramp is close to my house and workplace - I use Unleaded 91 fuel.

I'm not sure what to do, I am planning to buy an OBD2 Scanner to help track fuel usage and cost as I need a better way to handle it than my notes app

I found these two - any advice on which is better would be great

https://www.supercheapauto.com.au/p/matson-matson-bluetooth-vehicle-monitor/SPO7089190.html

https://www.supercheapauto.com.au/p/gofar-gofar-dongle-complete/SPO6458896.html

The GoFar looks a lot nice but I feel the ray is a bit on the tacky side of things, I am pretty sure I can use any fuel tracking app built for connecting to an OBD2 Scanner - there's a handful out there and Matson suggests one but the gofar seems to make trips/fuel and everything else a bit easier to track, I have store credit so would prefer to use supercheap Auto and these are the only ones that fit my need from what I can tell.

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On the side of this potentially being a mechanical issue - Can I chalk it up to car age & wear making it less fuel efficient or is there a troubleshooting route I can take before I talk to a mechanic, I'm happy to try anything that can be done with some basic tools and a driveway but I don't even know if this is something I can bring to a mechanic?