Among all the dire warnings regarding Mexico, the last one we’ve taken seriously was about the lack of petrol stations en route, or at least the large distances between them. To compound this, the car only takes premium – 91 octane – and I’m not prepared to risk lower, not yet, anyway. Lower octane fuel burns less cleanly and on a smooth-running engine like a V6, engine noises can be harder to detect, more subtle. Petrol is nationalized here, with fixed prices and station attendents doing all the work for you, but not every station has premium. And nor does the guy who sells gas from his cart.