My recommendation you quoted applies to smart only. If the manufacturer of your vehicle recommends 5W-20 then you should use that or a 0W-20. Most modern engines has some very small oil passages with filter screens and solenoids that operate the variable cam timing mechanism. Oil that is too thick can inhibit proper functioning of them. My Civic Si has used 5W-20 since new and it has over 176,000 miles on it and still rolling them up without a problem.Is that a general recomendation of strictly related to use w/ a smart? I ask because I have a vehicle that the manufacturer recommends 5-20W. So far it's been fine but mileage is getting up there.