WHY 5-40?
Hotshot
Joined: Jul 2005
Posts: 13,834
Likes: 25
From: Middle Tn.
5W40 protects weight wise the same as 15W40 in heat and is better in cold conditions at a lower temp. Being synthetic it also has better anti-coking properties at higher temps. Esp. Good for the turbo. JMHO.
Lead Driver
Joined: Dec 2013
Posts: 9,762
Likes: 115
I like 0W-40W, but usually all I can find is 5-40...
The truck coming with the FoMoCo semi-syn 5-30 is BS IMHO. Even though that is what I am running now, because the oil change was free.
If you are hear in the winter, the 5 part is mandatory, I don't think I'd want 15W motor oil in a vehicle in the winter in Alaska...
The truck coming with the FoMoCo semi-syn 5-30 is BS IMHO. Even though that is what I am running now, because the oil change was free.
If you are hear in the winter, the 5 part is mandatory, I don't think I'd want 15W motor oil in a vehicle in the winter in Alaska...
More Turbo
Joined: Jan 2012
Posts: 740
Likes: 152
From: USA
Trending Topics
Posting Guru
Joined: Dec 2015
Posts: 1,040
Likes: 9
5w40 covers all conditions and is synthetic. Why use anything else?
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Lead Driver
Joined: Dec 2013
Posts: 9,762
Likes: 115
If I were in Fairbanks in the winter, I would disagree that 5W is good enough... And even potentially in some of the areas around Anchorage that get colder than the airport here.
A summer trip to AK you won't find a condition outside of 5W-40.
A summer trip to AK you won't find a condition outside of 5W-40.
Posting Guru
Joined: Dec 2015
Posts: 1,040
Likes: 9
I live in Vermont, use 5W40 and it starts right up at -20.
Logistics Pro
Joined: Jul 2002
Posts: 4,821
Likes: 19
From: South Dakota
Manufacturers don design that way in medium and light duty trucks and cars.
There are many reasons for using 15w40.
First and for most is cost.
Secondly there are many uoas out there that show that a good 15w40 like delo or rotella does better in diesels with dpfs and egrs.
Thirdly, fuel dilution is an issue and is the main reason ocis beyond 7000 mi are a bad idea regardless of what oil you use.
The only value a 5w40 brings to the 6.7 is cold weather starting performance.
A lot of newer diesel owners run 15w40 spring to fall, and switch in the winter.
I just dumped my 5w40 for 15w40.
Lead Driver
Joined: Dec 2013
Posts: 9,762
Likes: 115
And fairbanks sees -50 to -60f, what's your point?
Mine starts up in Anchorage in -20f, although I can tell without being plugged in it isnt as smooth a start.
Mine starts up in Anchorage in -20f, although I can tell without being plugged in it isnt as smooth a start.
Tuned
Joined: Dec 2010
Posts: 460
Likes: 50
From: Washington state
I have used Dello 15/40 from the second oil change. I have 90,000 miles on her now. I live in Washington State in an area that it is unusual to get below 0 and most of the time is a above 20 degrees. The truck is parked inside a warm garage so no need for the expensive 5/40. I pull a 4 horse trailer from spring until November and a 5th wheel Rv in the summer . I am retired so it doesn't spend enough time outside in the winter that cold is a problem. I have thought of using 5/40 to see if the milage is better but it would have to be a lot better to justify the extra cost. Costco always has Dello. To each his own though.
Hotshot
Joined: Oct 2006
Posts: 10,135
Likes: 7,941
From: Texas
Think about plugged EGR's and longer turbo life.
Super Moderator
Joined: Aug 2003
Posts: 25,479
Likes: 738
From: Isanti, MN
Here's a snippet from the 2015 diesel supplement:
