Aramco, Exxon to refit Yanbu plant in 2013 -source

* Aramco, Exxon to shut refinery for clean fuel project * Clean fuel project to come online in 2013

* Shutdown to last 4-5 weeks, says industry source

* Firms investing $2.5 bln to cut sulphur emissions

KHOBAR, Saudi Arabia, Aug 28 (Reuters) - Saudi Aramco and Exxon Mobil (XOM.N) plan to shut their 400,000 barrels per day (bpd) Yanbu refinery in 2013 to bring on stream a new clean fuel project, an industry source said on Saturday.

Exxon and Aramco are investing $2.5 billion to reduce sulphur from diesel and gasoline at the jointly owned refinery.

The refinery, on the Red Sea coast, exports mainly gasoline and gas oil.

"Most of the refinery would be down for the clean fuels project," the source said.

The shutdown would take place around February 2013 and would last 4 to 5 weeks, the source, who declined to be identified, said.

The project will not change the capacity of the refinery, an executive from Exxon Mobil's chemical unit said last year. He had expected the project to come online by 2012. [ID:nL694614]

(Reporting by Reem Shamseddine; Editing by John Stonestreet)