Oil type confusion for 2017 F350 6.7… What do you all use?

Discussion
1

I keep getting different answers on what oil to use for my 2017 F350 6.7. Bought it last year, and I did the first oil change myself with Ford’s 10W-30 on my mechanic’s advice (had no issues). The dealership, however, has been putting in 15W-40 whenever I send it in for service. And online, I see tons of people recommending 5W-40.

The oil cap says either 5W-40 or 10W-30 is recommended, and I live in the South, where it’s only cold a couple of months out of the year. I have 5W-40 on hand but not sure if it’s the best choice. What’s everyone here using on their diesel trucks?

2

The manual actually recommends 10W-30 for normal conditions, 5W-40 for colder conditions or severe duty, and 15W-40 if you’re in warmer climates.

3

Sawyer said:
The manual actually recommends 10W-30 for normal conditions, 5W-40 for colder conditions or severe duty, and 15W-40 if you’re in warmer climates.

Exactly, and if you’re doing heavy towing or using biodiesel, 5W-40 is ideal. Ford uses 10W-30 mainly because it’s cheaper and helps with fuel economy, but 5W-40 is better for engine longevity.

4

I run 5W-40 synthetic year-round. Works great.

5

5W-40 full synthetic, specifically Rotella T6 here.

6

Depends on how much you’re towing. 10W-30 is fine, but if you’re doing heavy pulling, especially in the South, 15W-40 could be better. Just let it idle for a bit before driving so oil can reach the turbo.

7

I used to run only 5W-40 Motorcraft but recently switched to Amsoil and kept the Motorcraft filter. I change it every 5-6k miles since the emissions system is rough on oil. OEM filters are a must.

8

10W-30 is recommended. I wouldn’t use 15W-40—there are stories of people throwing rods using that weight. If it was under warranty, Ford could deny coverage for that reason.

9

Frey said:
10W-30 is recommended. I wouldn’t use 15W-40—there are stories of people throwing rods using that weight. If it was under warranty, Ford could deny coverage for that reason.

Here’s a link: https://images.app.goo.gl/k5QFTmAgSZQNTijX8. Ford does approve 15W-40, especially for biodiesel. Warranties won’t be denied because of it.

10

@Ashwin
That’s not true. I’ve got friends at Ford who’ve seen rods thrown from 15W-40 use. It’s too thick for the 6.7.

11

Frey said:
@Ashwin
That’s not true. I’ve got friends at Ford who’ve seen rods thrown from 15W-40 use. It’s too thick for the 6.7.

There’s no official TSB saying 15W-40 is an issue. Ford’s own manual approves it.

12

Frey said:
@Ashwin
That’s not true. I’ve got friends at Ford who’ve seen rods thrown from 15W-40 use. It’s too thick for the 6.7.

Been using 15W-40 in my 2011 with no problems.

13

Frey said:
@Ashwin
That’s not true. I’ve got friends at Ford who’ve seen rods thrown from 15W-40 use. It’s too thick for the 6.7.

Highly unlikely 15W-40 is causing those issues, especially in warmer weather.

14

Frey said:
10W-30 is recommended. I wouldn’t use 15W-40—there are stories of people throwing rods using that weight. If it was under warranty, Ford could deny coverage for that reason.

When I worked at Ford, we only flagged oil types if there was something clearly wrong, like contamination. I’ve even seen a case with red oil (looked like it had trans fluid in it) and Ford still covered it. 15W-40 should be fine if you’re warming it up before driving.

15

I’d go with 10W-30 or 5W-40 synthetic. 6.7s can retain about 2 quarts of dirty oil even after a change, so synthetic 5W-40 is safer for longer intervals. Personally, I use Shell Rotella T6 5W-40 and change every 5k miles.

16

@Ainsley
Thank you! New to diesel, this clears things up for me too.