The engine is a 4.0 OHV engine, and Ford specifically does NOT recommend a 20 weight for this engine. 5w30 is recommended in the owners manual, and 10w30 is acceptable. The engine has 165,000 miles on it and uses about 1 qt every 1000 miles due to slight leaks and some internal consumption. I don't want to use an expensive oil (i.e. synthetic) because of the consumption. The vehicle is used on short trips around town - soccer mom style. Summer temps are in the mid 90s, and winter temps get as low as 10 degrees. But we keep it in a garage, so it never sees cold starts in this range. Looking at UOAs of various oils, it seems all the dino 5w30 and 10w30 oils shear down to a 20 weight or near 20 weight. 10w40 oils shear down to 30 weight. Are there any 30 weight dino oils that won't shear? Should I use a 10w40? Should I mix some HDEO 15w40 and 5w30? Other suggestions?