I have always believed that you should only put 5w30 semi or fully synthetic oil in a zetec engine. Any thicker and it does not lubricate the engine properly.

However many people argue that a slightly thicker oil works fine and is more suitable in a higher mileage engine where the thinner 5w30 will leak past the piston seals and be burnt away. Haynes lists 5W/30, 5W/40, 10W/30 or 10W/40 as all being suitable grades but warns not to go any thicker as this may cause problems. I have a very high mileage (175k) focus that has been ran for a good few years by the previous owner on 10w40. It currently loses no/ very little oil.

I am unsure whether to put 5w30 in there at oil change or stick with a 10w40. I am leaning towards a 5w30 as thats what I think should be in there, but just wondered what everyone else thought.

 

in the summer you will be fine running 10w40 but in the winter run 5w30.
the colder it is the thicker the oil and last thing you want is an eninge runing dry until it heats up.

 

I was thinking same, checked autodata and it says for all climates use 5w/30 but doesn't say whether its semi or fully synthetic

 

I would run the 5/30 in it mate !

I put Magnatec in mine and although cars will run on other grades I believe it pays to use the recommended viscosity !

There you go mate.

http://www.opieoils.co.uk/p-754-cast...d-by-ford.aspx