I know that the recommended oil viscosity for the zetec engine is a 5w30 but for the older zetec engine like my 95 fiesta 1.6.16v would a 10w30 or even a 10w40 provide better protection although the 40 maybe to thick an oil?

 

i have a 1995 fiesta 1.6 and i use castrol magnatec 10w40 and thats fine, i've even done a track day using 10w40 no prob. although that reconmended oil would be best.