15W-40 Synthetic Diesel Motor Oil.....

[thailoht]

The mfg specifications for my Isuzu 3.0L diesel lists 15W-40 diesel and other grades of motor oil....but not 5W-40.

When I went to Cockpit, B-Quick and Shell service stations, they all only stocked diesel 5W-40 synthetic oil and after consulting their shop's charts, recommended it could be used in my engine.

Does anyone know the reasoning of why these companies collectively choose to use only the 5W-40 grade of synthetic oil in their customers vehicles in light of mfg specifications that call for a different oil grade?

[transam]

Your manufacturer states a thicker grade because of their tests on engine longevity. If me l would locate the correct grade for the ambient temperatures of where you live. Your hand book will tell you the correct grade for this. Saying that, synthetic is an engines best friend and l would not worry much about the use of a 5w-40.

[anon210]

Apparently a question of thickness of the oil and they are quite interchangeable if I refer to this forum: http://www.dieselbombers.com/dodge-truck-cummins-turbo-diesel-forum/71179-15w40-vs-5w40.html or this one: http://www.thedieselstop.com/forums/f28/5w40-vs-15w40-261816/

[Kwasaki]

Your manufacturer states a thicker grade because of their tests on engine longevity. If me l would locate the correct grade for the ambient temperatures of where you live. Your hand book will tell you the correct grade for this. Saying that, synthetic is an engines best friend and l would not worry much about the use of a 5w-40.

Yep !! 40 is the important bit 5w be Ok if you driving to Iceland.

[transam]

Your manufacturer states a thicker grade because of their tests on engine longevity. If me l would locate the correct grade for the ambient temperatures of where you live. Your hand book will tell you the correct grade for this. Saying that, synthetic is an engines best friend and l would not worry much about the use of a 5w-40.

Yep !! 40 is the important bit 5w be Ok if you driving to Iceland.

Yeh, the thicker oil, 15w, is to take care of a cold engine. Isuzu obviously has concerns about protection on start up. Sooooooooooooo, if your keeping your ride for a few years or many miles then put what they recommend, don't take any shit from someone who doesn't know the facts.

[kwonitoy]

The "W" stands for winter and that's the viscosity of the oil at a lower temperature, once you hit 100C in the engine the oil's viscosity will be the higher 40 rating.

We'd use 5w-40 or even 0w-40 oil in Canada in the winter in the diesel's

It's not really applicable here, the 40 is the important part, use the 5w-40 without a worry

[thailoht]

Your manufacturer states a thicker grade because of their tests on engine longevity. If me l would locate the correct grade for the ambient temperatures of where you live. Your hand book will tell you the correct grade for this. Saying that, synthetic is an engines best friend and l would not worry much about the use of a 5w-40.

Once again, "Thanks guys for clearing that up!" I had totally forgot about the 5W- / 10W- principle about and its effects on oil grade that we used during seasonal changes.

[seedy]

Oil uses a friction modifier to enable viscosity changes - from 5 to 40 or from 15 to 40 weight, etc

Some believe that the range of 5 to 40 requires too much of the additive, and so recommend a smaller range - like 15 to 40

[VocalNeal]

Does the ISuzu book sat 15W-40 synthetic or simply 15W-40? It seems that most fully synthetics have a lower "winter" number than conventional oils. A cursory look at Shell, PTT, Caltex and Petronas did not yield a 15W-40 fully synthetic only 5W-40

This is what castrol says

[thailoht]

Does the Isuzu book say 15W-40 synthetic or simply 15W-40? It seems that most fully synthetics have a lower "winter" number than conventional oils. A cursory look at Shell, PTT, Caltex and Petronas did not yield a 15W-40 fully synthetic only 5W-40

This is what castrol says

The Isuzu book says 15W-40 (not synthetic) and other grades.

After discovering the same thing that your cursory look revealed, I think I went into a TIT mindset when starting this post and simply 'forgot to remember' what I had learned long ago about oil viscosity.

[thailoht]

Taking this engine oil discussion to yet another technical level:

My Isuzu book also states that 10w-30 CF-4 certified oil can be used in its 3.0L diesel engines.

What would be the long-term engine performance outlook if I operated this 3.0L engine solely on Mobil One 10w-30 CF fully 'Synthetic' certified oil, (not CF-4)?

Does anyone know the technical (and real world application) differences between CF-4 certified oils and their predecessor, CF certified oils?

[Kwasaki]

Taking this engine oil discussion to yet another technical level:

My Isuzu book also states that 10w-30 CF-4 certified oil can be used in its 3.0L diesel engines.

What would be the long-term engine performance outlook if I operated this 3.0L engine solely on Mobil One 10w-30 CF fully 'Synthetic' certified oil, (not CF-4)?

Does anyone know the technical (and real world application) differences between CF-4 certified oils and their predecessor, CF certified oils?

Engines are usually designed to take a specific oil range that's suitable for the vehicle.

Say like Toyota has it's own named plastic canned oil 10w30 but it is supplied by one of the oil manufacturers.

There are so many sites on the subject, here's another :-

http://www.driverste....co.uk/oils.htm

Thailand gets very hot so using a 40 grade as I do is better IMHO, whether it's syn or semi I am not boshed about it.

No worries.

[thailoht]

There are so many sites on the subject, here's another :-

http://www.driverste....co.uk/oils.htm

Right- On!!

Once again, you have hit the nail on the head by posting another excellent site!!