I’ve been running 10W30 in my 6.7L for over 12 years and nearly 200,000 miles and not had a single failure yet.

 

I was referring to 15W40.

 

This is going to definitely stir up some mixed opinions regarding this as generally this gets taken down a rabbit hole.

All over the Facebook pages, people will either eat you alive for saying you use 15W40 in your truck, even if the type of oil meets Ford's new approved standard, and many have used it for 500k+ miles, in cold climates, and even when not prefilling the filter..... (little added controversy lolol)

In my 2016, I have used Motorcraft 15W40 for the past 50k miles (now at 100k), no apparent issues but I am worried they could come. The dealer puts in 15W40 and they pretty much laughed at me when I inquired about 10W30 or 5W40 as they said 15W40 was the only thing that should go in this truck and I would need to make an appointment a few weeks in advance if I wanted that as they just simply do not carry it. I am in North TX which is generally a warmer climate so maybe it wont be as bad, but with some cold weather coming up, and the cold weather we have had the past few years, I just hope I didnt do any damage. I let truck warm up before driving it so I dont go right off the bat.

Also I don't necessarily fell comfortable changing oils at this point due to the mileage of the truck and how I (and previous owner) have always used 15W40 since new, and I have also heard rumors that the engine can be quite sensitive to suddenly changing to a different weight.

Can anyone point me in the right direction here, possibly overthinking but it seems to be a a controversial subject.

Happy Holidays!!!

They laughed at you for putting in the manufacturer recommended oil viscosity? That seems abnormal. I've used differing weights of oils outside of manufacturers recommendations in several of my previous vehicles with no ill effects. Might have been harder on the pump. Now I generally stick to the factory recommendations.

If you're using b20, the manual says 5w40.

 

I have heard that 15w40 along with tight internal tolerances and cold weather use could be to blame for engine damage in some early 6.7l. I've also heard the tolerances have loosed up some in later 6.7l engines so not as sensitive to that oil in the cold.

I wonder just how cold it has to be though for it to be a legitimate concern? The OM shows use of 15w40 down to 20 degrees, I personally would have no fear of using it in the suggested temp range. The dealers in this part of Cali use 15w40 as standard fill in the 6.7l oil change.

 

I have heard that 15w40 along with tight internal tolerances and cold weather use could be to blame for engine damage in some early 6.7l. I've also heard the tolerances have loosed up some in later 6.7l engines so not as sensitive to that oil in the cold.

I wonder just how cold it has to be though for it to be a legitimate concern? The OM shows use of 15w40 down to 20 degrees, I personally would have no fear of using it in the suggested temp range. The dealers in this part of Cali use 15w40 as standard fill in the 6.7l oil change.

20F is probably a safe estimate, I know seeing that in the manual. Not sure if mine is considered early or late being a 2016.

i have started it up in -3F oil temp one time with no issue. And put 30k miles on it since then. I guess every once In awhile it’s fine but not for continuous harsh winters up in the northern states!

only thing mine gets is the typewriter noise every oil change but each oil can get that and I just ignore it.

 

No issues unless you are operating in the cold ( think Wisconsin etc)

I would suspect anything that dealership tells you in the future though given their attitudes…

 

15W40 is the foundation of diesel motor oils. Is it required anymore? No. Is it still practical in A LOT of applications? Yes.

My next oil change I'm going to 15w40 synthetic from 10w30 Ford oil.

 

10w30 for fuel mileage and 5w40 synthetic for engine longevity.

 

15w40 here, in both a 16 and my 21. 5w40 if you have to start below say 10, 15 degrees consistantly, but frankly the 6.7 spins so fast and starts so easily, that a 15 will work to zero, as long as you give it a moment to warm up. Pick one off the approved list. Lots of Rotella lovers, I like the Delo silver bottle synthetic offering, the OP using is MC oil is just fine, It's a premium offering and might under some conditions, edge out Rotella. I like a 40 weight if towing, or with bio fuels, I just feel having a slightly thicker oil film is beneficial under load. You don't need a 15w40 though, many many trucks out there motoring along on 10w30 and 5w40. Just pick one, keep it changed with a decent oil filter, (another whole discussion there) and make sure the oil is on the approved list.

 

Keep driving your truck and dont worry Read your first post again and think about it logically. You've been using 15w-40 oil this whole time with zero issues. so did the previous owner... Now at 100k the engine tolerances are a little more forgiving. The 15w-40 oils would only work better in your scenario. based on a "more worn engine" if we could even call it that with only 100k miles.

Ford also told everyone the 6.0l was reliable and many dealers fought them to put studs in but Ford whined like a hippy. Manufacturers are not always right, hence why engineers are great on paper but real life can show any flaws and over sites that need correction. is 15w-40 perfect no? But is it an engine killer highly doubtful. How many old school people are still only running 15w-40 even in the winter in snow states. More than youd ever believe lol.... I know more that do than dont.

Also most of our 6.7s run it even when its -20 and they still start and warm up without exploding. I had never even used full synthetic oil until 2018 for crying outloud lol.