Which oil do you think is the best among these two.

Winter versus summer formulations

 

They're both 40 weight oils the 5w or 15w just refers to the temp it will flow at for a cold start. 5w cost more than 15w. They also make 0w40. When it gets that cold people usually idle it anyway or plug it in at home or have coolant heaters, etc.

Just get the 15w40

 

My preference. I us the chevron XSP 5w-40.
Before at 15W-40 XLE I’d idle when it got under 11 degrees. With the XSP 5W-40 I idle around 2 degrees. Again, those are my preferences. I save on fuel by not idling at night enough to make the cost difference up for the year. I run the same oil in my X15 and Carriers.

 

As others have stated, depending on the weather you predominantly operate in. Myself, I’d go with the 15w40. Granted I am in the Permian Basin of Texas, as ‘winter’ is relative term.
But as company driver, I put in the engine what am told. If I was ‘director of maintenance’ in our frac fleet( pumps, blenders, etc) that run for days on end, and may not be shut down for any length of time but for quick p.m., I’d authorize a straight 30w diesel motor oil.

 

The DA Lubricant oil is better because it has more Zinc in the formulation

 

Both good.

There are temperature range charts in truck/engine manuals with recommended oil viscosity for your operating environment.

 

Should be a recommended oil sticker on valve cover. Brand is preference, but viscosity is usually listed also. T6 is for newer engines.

 

Define old? And no, not really

T6 is full synthetic
T5 is semi synthetic
T4 is non synth

They all meet ck-4 api standards, which are backwards compatible to cj-4

As a rule of thumb, any current rated oil (as long as viscosity is correct) will work in older engines, BUT synthetics and semi-synthetics do tend to exacerbate any oil leak/consumption you already have with the refined oil.

i.e. older engines leak more with t6 than t4