Went to pep boys and looked for 5w20 weight oil for my 2005 st. The only 5w20 that i found were castrol gtx and penzoil. There were full synthetics but i will wait on synthetic oil till i get some more miles. In the owners manual it says to use motorcraft 5w20 semi synthetic. I'm assuming it's in the car from the factory. My question is are all 5w20 semi synthetic? The motorcraft says semi syntheitc but the penzoil and castrol gtx just state it is regular dino oil. I would rather not get raped by my ford dealer on the motorcraft 5w20. Also i would like to stay with a semi synthetic since that's what the manual says. I will go with 5w30 or even 10w30 in the summer months after breakin. I was wondering if anyone knew the specifics of all the 5w20's the stores sell. I had heard from someone that all the 5w20's are semi synthetics. Your answer will probably say just use the motorcraft but i will ask these questions anyhow.