whats the point of using a 50w in the engine? its not going to give you added protection over 5w20. take a look over at bitog and look at some of the mod engine test results all of them show higher wear numbers when you go over 10w30 and they all show very nice looking numbers when you use 5w20.
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If it doesn't fit, FORCE it.
If it breaks, well, it needed replacing anyway.
1999 5.4 Expedition. 5w30 since we bought it at 50,000 miles about 2 1/2 years age. About 80,000 on it now. Motorcraft 820S filters. Uses about 1/2 quart in 2000 miles.
15W as a base stock is a bit thick for start-ups on a modular engine. You want oil to the top of the engine as soon as possible due to the overhead camshafts and such.
Oil is designed by using a base stock number say 5W for instance and then has additives to make it a certain thickness when hot = 20.
So 5w20 flows like 5wt when cold and 20wt when hot.
15W40 is thicker when cold 15wt and will not reach the top of the engine as fast when cold and 40wt when hot is not required.
I have towed 7000lbs in 98degree weather with the a/c on and have never used any oil between changes and have had no adverse effects from the 5w20 in 54,000 miles.
i live in south texas and i have always used 20/50 in all my trucks doesnt get to cold here. in colorado for 7 winters sure we used the lower viscosity. havent heard that this is bad .
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