5w-40 vs 15w-40 startup smoke

[DEWFPO]

am concerned about the 5W-40 when the temps can get up to 80 degrees F this summer. The average daily summer highs are usually in the 70's.
Jim

Why would you worry about a 40 wt. at 80F ?

DEWF{P

 

[jlrsn]

Why would you worry about a 40 wt. at 80F ?
DEWF{P

Even though I regularly tow up to 12k lbs. through up to 122+ degree F temps crossing AZ with my F250 PSD using 15W40 I've always operated my L39 at lower temps. What amazes me is how smooth and quiet my L39 operates with the Fully Synthetic Mobil 1 Turbo Diesel Truck 5W-40 Engine Oil vs the prior start-up noises at below zero starts. Prior I never did trust 5W-40 oils as I came up through the original multi-weight oils and the problems associated with the formulations from the late 50s thru the 70s. I realize that those days are long gone but it takes a while for me to trust oils.