In conclusion, 15W-40 engine oil is a specialized viscosity grade designed for heavy-duty applications. Its excellent lubrication and wear protection properties make it an ideal choice for diesel engines, construction equipment, and commercial vehicles., In 15W-40, the first number, 15, shows how thick the oil is when it is cold. So, it is followed by the letter “W,” which stands for “winter.” The second number, 40, shows how thick the oil is when the temperature is high. How is 5W-40 oil different from 15W-40 oil?, The “15” in 15w40 means it flows well on chilly mornings, while the “40” means it holds up under high temps and heavy loads—perfect for those long summer days when engines run hot and hard., Rotella T5 Triple Protection 15W- 40 Diesel Engine Oil. Get free shipping on qualified 15W-40 Motor Oil products or Buy Online Pick Up in Store today in the Garage Department., Find the right O'Reilly Conventional Motor Oil 15W-40 1 Gallon for your vehicle at O'Reilly Auto Parts. Place your order online and pick it up at your local store for free., GTX Diesel is a 15W-40 diesel engine oil formulated to help extend engine life. What is the best 15W-40 oil to use? If you need a 15W-40 diesel oil, Castrol ® GTX ® Diesel helps extend engine life, protecting against the wear and tear of severe weather, rough roads and heavy tows..