The FIA has confirmed Mercedes' Spa engine update will not be subject to stricter oil burn regulations set to come into force from the Italian Grand Prix onwards.

In an attempt to clamp down on teams burning oil for performance gains, all new engines introduced from the Italian Grand Prix onwards will be limited to oil consumption of no more than 0.9 litres per 100km. But because it introduced its fourth and final engine update ahead of the Italian Grand Prix, Mercedes' latest spec of engine will still be subject to the previous consumption limit of 1.2 litres per 100km and can continue to run legally at that level for the rest of the year.

The subject of oil burn has been under the spotlight since the start of the season when the FIA reminded teams that it is illegal to gain a performance advantage by using oil as fuel. The governing body upped its monitoring of oil consumption during the first half of the season, and at the Azerbaijan Grand Prix sent a note to teams reminding them that it would view any attempts to use combustion-enhancing chemicals in their oil as a breach of regulations.

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Amid concerns some teams were still gaining an advantage from oil burning, a technical directive was issued ahead of the Hungarian Grand Prix making teams aware that any engine introduced from the Italian Grand Prix onwards would be subject to the tighter oil consumption restrictions. After some confusion as to which limit the latest Mercedes engine would need to adhere to, an FIA spokesperson clarified the situation on Tuesday.

"We had several questions about oil burn from Monza onwards, a topic covered by a technical directive issued last month," he said. "The main question centred on whether engines introduced at Spa will be subject to the expectation that the 'oil consumption of any ICE element of the Power Unit introduced from the 2017 Italian GP onwards to be less than 0.9L/100km'.

"Article 23.3b of the Regulations states: 'Any of the six [Power Unit] elements will be deemed to have been used once the car's timing transponder has shown that it has left the pit lane.' So, to be clear, 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."

Ferrari is yet to introduce its fourth engine specification of the campaign and will therefore be restricted to an oil consumption restriction of 0.9L/100km on that unit when it does so. The same applies to Mercedes' customer teams when they receive their latest upgrade, even though the spec of engine will be the same as the Mercedes works team.

When Mercedes boss Toto Wolff was asked if the subject of oil burn might flare up into a public row with Ferrari before the end of the season, he said: "We are fierce competitors, and the relationship we have is that we stick our heads together if there is a problem and discuss it behind closed doors. It hasn't come up.

"We need to be careful that things are not made up in public that are just not right and not true. So far, I'm easy about it."