.....in a vehicle specd for 5w30. Vehicle is a 02 Chevy Silverado w/ a 5.3l. Thinking of trying 3qt of Motorcraft 5w20 w/ 3qt of Motorcraft 5w30. It will be getting very cold (-20 to -40sf) here soon in the north part of the country, and thinking of trying this. Using Mobil 1 right now, but can get two oc's (5k) w/ the MC for the price of one w/ the Mobil. Any thoughts or suggestions appreciated. Thanks!