One of the dealers near me uses 15w40 year round in all their diesels including 6.7. Will this hurt this motor, or is it better? No other manufacturer, the big 3, use any less than 15w40 even in the new diesels.

 

That sounds like it is for warmer climates. (15W40) If you live is a seasonal area, with cold winters you might want a thinner oil in the winter. The higher the number, the thicker the viscosity for hot areas. If towing in heat you may want the 40 number. If the dealer says it is okay for the area it probably is for that area.

I use 10W30 for both summer and winter and I am in semi-northern Ontario, Canada. And if you run synthetic you would probably have even more protection for the engine, although it costs more.

My 1 and 1/2 cents.

 

Its a cold northeastern climate. My older trucks always started well 10 below 0 on 15w40, yet in Fords owners manual it shows + 20f for 15w40.

I think I will do my own changes from now on, looks easy and use 5w40 synthetic year round.

 

Yep, Rotella T6 5w40 year round for me -40 to 90F around here.

 

I use Motorcraft 15w-40 year round but it doesn't get that cold down here in AL.

 

I just switched to Mobil Delvac 15w-40. It's cheaper than the Motorcraft and seems to be a good oil. I don't know if any of it makes a difference though, really.

I'm in the southern climate, it's hot here, I tow a lot, I do travel to the mid west for work in the winter but I'm not worried about that.

I've heard guys say that you want the heaviest oil you can stand in a diesel but I'm not really sure if it's really that important or not.

 

The "W" does not stand for the weight of the oil it stands for how the oil will flow when its cold or "Winter" months. 5W 40 will flow better when its cold vs. 15W 40 its a blended oil but they both offer the same protection for the motor at operating temps.

 

Why spend extra for synthetic? I could run 15W40, and in cold, use block heater that came with my truck.

 

Yeah...hot is an understatement this year.
An 8F start is the coldest my truck has ever experienced.
It turned over right to 1,100 RPM and I let it run that way for a few minutes.

 

My coldest was 3 I think in central Illinois last winter. The tweeters I have are lliquid cooled and they were frozen, I didn't have audio for a few minutes! But everything else was rather boring, except my air compressor was seized too.

And doc, it's my mistake for using the wrong words, same meaning to me though, I tend to let the little semantic differences go but thanks for clearing it up for the benefit of others. Thick, heavy, viscosity, weight, etc....the 40 is the weight, right?

 

Rotella T6 5w40

 

ruschejj

Sorry I didn't mean for that to come off that you were being literal about it being the weight. Some times people get caught up on the "5W" or "15W" and think it relates to weight of the oil.

The 40 in the oil rating actually relates to a SAE grade that is determined by how long it takes for a given amount of oil to flow at a certain temperature usually 210 Deg. From A to B so to speak.

So if you have a 5W 40 oil then, in cold temps the oil will flow like a SAE 5W(Cold grade) motor oil and will flow and have the viscosity of a SAE 40 grade oil at operating temperature. This blend helps to get the oil up in the motor to moving parts when its cold but will have the viscosity of the higher number to protect the parts.

 

I have always used synthetic, I think it is better oil.
The manual says 15W40 is good to 20F, it gets a lot colder than that here. Whe I can't plug in and need to start at -20F or colder I am happy to have the T6 5W40 in there. I have had no issues with this truck in very cold weather.

 

I'm not a fan of changing between dino & synthetic. I agree synthetic is superior, and may European cars use it standard from factory. But changing between the two based on ambient temp is, just doesn't seem like its good for the engine and its seals.

 

I went for 15W40 this time due to product availability... last time I used 5W40 so I will compare the differences, if any. Both types are synthetic.

I know people can talk about oil for hours on end... how the '40' weight is actually thickened by additives and when the additives wear out the oil goes back to the cold weight since it can't deteriorate any more than what it originally started off as. But if you do your oil changes it should never get to the point where those additives wear out anyway.