From Mobil Website.
Ask Mobil Ask Mobil
Any Concerns with Using a 15W-50 Viscosity Motor Oil When Towing a Heavy Load?
Ask Your Stickiest Question. . . Or ask us something you’ve always wanted to know about using our products. We’ll sort through all the submissions and present the best questions to our automotive experts. We'll share the questions and their answers here.
Question:
Any Concerns with Using a 15W-50 Viscosity Motor Oil When Towing a Heavy Load?
I have an '07 Tundra 5.7 I-force. Toyota calls for 0W-20 or 5W-20. My mechanic wants to run 15W-50 since I tow a 7500-lb travel trailer on a monthly basis. I have noticed tapping when the engine is cold when I use 15W-50. Will the heavier weight oil damage the engine?
-- Kevin Edewaard, Tallahassee, FL
Answer:
We recommend that you follow your manufacturer's recommended viscosity grade. The engine has been designed hydraulically to handle the 20 grade oil. It will also provide better low temperature pumping at start-up, allowing oil to get to the top end quicker which may quiet the tapping you hear on start-up.