Modern Diesel Engines

DRussell

Well-known Member
Diesel engine manufactures recommend fairly low viscosity engine oil when the engine is new. As an example, John Deere Plus 50 engine oil has a viscosity rating of 0W-40. Another example, VW recommends 5W-30 for their TDI engines. I've always heard this recommendation for low viscosity oil is because of the very tight tolerances in a new engine. Obviously as an engine gets older wear happens.

I realize that other factors have to be considered for emissions purposes such as low ash oil when there is a diesel particulate filter, but I'm talking specifically about the viscosity rating.

At what point should a higher viscosity engine oil be used, or should you always use the recommended viscosity oil no matter the age/hours on the engine?
 
Always use what the mfg says.

Sometimes the viscosity varies by the ambient temperature, but that too will be specified.
 
(quoted from post at 15:12:40 11/20/18) Diesel engine manufactures recommend fairly low viscosity engine oil when the engine is new. As an example, John Deere Plus 50 engine oil has a viscosity rating of 0W-40. Another example, VW recommends 5W-30 for their TDI engines. I've always heard this recommendation for low viscosity oil is because of the very tight tolerances in a new engine. Obviously as an engine gets older wear happens.

I realize that other factors have to be considered for emissions purposes such as low ash oil when there is a diesel particulate filter, but I'm talking specifically about the viscosity rating.

At what point should a higher viscosity engine oil be used, or should you always use the recommended viscosity oil no matter the age/hours on the engine?
One man's opinion: Stick with the manufacturer's recommendations.
 
The viscosity is more for the injector pump than bearing lubrication. Stick with the recommended!
 
"At what point should a higher viscosity engine oil be used"?

That's the thing, YOU CAN'T TELL by lifting the hood and looking at the outside of the engine. The only way to know would be to tear the engine down and measure for wear. It would be about the same cost to just replace the engine with new, not to mention a whole lot less work.

Basically it's not worth trying to find out if you need higher viscosity, and in modern engines just randomly going to a higher viscosity can do more harm than good.

Besides, higher viscosity oils hardly ever do anything to improve the most obvious symptom, low oil pressure.
 
Are 0W-40 and 5W-30 really low viscosity oils at normal operating temperature? The first number 0W and 5W are measured at a low temperature and the second number 40 and 30 are measured at normal operating temperatures, I don't remember the exact temperatures.
 

It is hard to believe that the manual in my truck is the only manual that addresses this. Has no one else read this in their manual? Mine says to use the light oil unless towing or operating at high temperatures. I am not going to go looking up now but I believe it said to use 15-40 under those conditions
 
All these threads about oil. Pretty easy to find out what you need, every second, third, fourth, ????, oil change send a sample out to be analyzed. That will catch anything ugly in your engine before it is a problem for less than a dinner out at a NICE place.
 
Engine parts now are so hard, engines really don't wear unless the engine is just flat abused. Just use the recommended viscosity no matter the miles. I have several customers at my shop running 5w30 in 300K+ mile 6.0 GM trucks.
 
I have followed the owners manual for our JD 4600, when it was new I used 5-30, but it was only recomended for use up to 85F. So when it got above that I would put it away and go fishing! After about 500 hours I started using 15-40 Delvac, which is suitable for temperatures from 0- 110 F. I just make sure if it's cold (<32F) I preheat it. It's in a garage and has both a block and oil pan heater, and I very seldom use it when it's below 32F, it always starts immediately.
 
Yeah, engine parts are harder , in some cases, primarily cylinder bores. But the tolerances are much closer, and the surface finish is held much tighter , allowing much longer life to the engine. Things like crank diameter used to be +/- .025, now are +/- .0005 (Metric)
 

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