XMs were offered with several engines, from 2.0 carburettor to 3.0 V6 24V petrol and 2.1 to 2.5TD diesel. Mine is a mid-range petrol, a 2.0 Turbo CT (Constant Torque) engine, delivering about 145bhp (there was a later 2.0 Turbo CT which delivered 150bhp). I find this is a powerful enough car and fuel consumption is not excesive... But, remember, this is a big car with a perhaps 15 years old engine design so don't expect to get high mileages from it. Anyway, I am happy with the 10.5 liters/100km average consumption I get.
Engine bay, despite the picture first impression, is not too crowded (look at a 3.0 V6 24V and you will see the difference!). In fact, you can see the ground from engine bay in my car. Try this on a 24V :-)!
I hope to locate a 'correct' right one