With a new oil burn limit of 0.9 litres per 100km coming into force at the Italian Grand Prix, Mercedes pre-empted that cut-off point by bringing its fourth and final power unit into play in Belgium last weekend.

According to an FIA technical directive issued by the FIA in July, engines introduced before Monza would be allowed to run at an oil burn level of 1.2 litres per 100km.

However, there was subsequently some confusion about whether the ruling on the limits was superseded by a separate regulation that states customer units have to be at the same specification as the works outfits.

If that was the case, then it was suggested Mercedes would have to comply with the 0.9l limit when its customers moved on to their final engine.

But ahead of the Italian Grand Prix, the FIA has confirmed that Mercedes will only have to comply with the 1.2l limit that was laid down in the technical directive – because the engine has already been used.

The ruling does mean, however, that when Mercedes customer teams introduce their final units, they will have to run it at the 0.9L level.

An FIA spokesman said: “If an engine (ICE element) is introduced at or after the Monza race weekend, its oil consumption needs to be below 0.9L/100km whenever it is used.

“If an engine (ICE element) has been introduced at or before the Spa race weekend, its oil consumption needs to be below 1.2L/100km whenever it is used.”

The FIA deems that has engine has been used as soon as a car’s timing transponder has been triggered by leaving the pitlane.

The Mercedes move to bring its final engine to Spa was understood to have caused some unease at Ferrari, because the Italian outfit had not been expecting anyone to bring new engines for that weekend.

Furthermore, it also means the Maranello outfit will have to run its new engine – when it comes – at the 0.9 litres per 100km limit.

The issue of oil burn had become a talking point in Belgium, but Mercedes boss Toto Wolff made it clear he was happy to speak to Ferrari about the matter if there was anything they were unhappy about.

“We are fierce competitors and the relationship we have is that we stick our heads together if there is a problem, and we discuss it behind closed doors,” he said, when asked by Motorsport.com about the oil burn situation.

“It hasn’t come up. We need to be careful that things are not made up in the public that are just not right, and not true. So far, I’m easy about it.”