chrislondon

My fiesta si recently purchased has been using a 10w40 oil,reading here and elsewhere the correct grade is 5w30 although I guess 10w40 is ' ok '
I realise there will be performance loss and fuel economy is poorer with the 10w40.
Can the engine be damaged due to the increased friction from a thicker oil and if ' downgrading ' the oil viscosity will gaskets leak,will wear tolerances from the 10w40 oil cause problems?
Its a 95 fiesta,some 54000 milage.
Think its a series 2 zetec engine so it might tolerate a 10w40 oil and be immune to the problem of sticking valves/tappets in earlier zetec's.
Is a 5w30 enough protection in a hot engine,summer months ect.
Any professional opinions & experiences would be grateful.
Great forum and advice given.
Thanks.