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Old 03-18-2020, 02:02 PM   #1
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Synthetic Oil?

Is it ok to use semi-synthetic oil in Cummins ISB 6.7 360? Installed in a 2019 Tiffin Allegro RED 37PA. Allison 3000 Tranny
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Old 03-18-2020, 03:01 PM   #2
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Did you think about calling Cummins ? That is what I would do
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Old 03-18-2020, 05:15 PM   #3
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Link to Cummins 6.7L ISB service page:
6.7L Cummins Maintenance Schedule & Service Information

I use Shell Rotella T6 (full synthetic oil in our ISB. I use Rotella T3 in our ISX, but have used T5 once when it was on sale for the same price as T3.
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Old 03-18-2020, 08:15 PM   #4
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Is it ok to use semi-synthetic oil in Cummins ISB 6.7 360? Installed in a 2019 Tiffin Allegro RED 37PA. Allison 3000 Tranny
The engine is designed to run for 350,000 miles on dino-oil before an overhaul might be needed, they have lasted 750K. Why spend the extra money?
When you have time read this old thread: Synthetic lubricants - aren't?
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Old 03-22-2020, 11:32 AM   #5
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The engine is designed to run for 350,000 miles on dino-oil before an overhaul might be needed, they have lasted 750K. Why spend the extra money?
When you have time read this old thread: Synthetic lubricants - aren't?
It will probably last a lot longer than 350k either way, a couple advantages of synthetic include better detergent package, the inside of the engine stays cleaner, and more stability, you can push your oci out a bit longer. I've come to the point I always use synthetic, the price isn't that high for the advantages, and if you change out half as often it gets closer to a wash price wise, my sprinter goes 20k on an oil change and I change the filter at 10k.
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Old 03-22-2020, 07:17 PM   #6
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It will probably last a lot longer than 350k either way, a couple advantages of synthetic include better detergent package, the inside of the engine stays cleaner, and more stability, you can push your oci out a bit longer. I've come to the point I always use synthetic, the price isn't that high for the advantages, and if you change out half as often it gets closer to a wash price wise, my sprinter goes 20k on an oil change and I change the filter at 10k.
I have no doubt dino oil will last 20K miles either. An oil analysis should be done any time OEM oil change interval is ignored though.
Cummins states the type oil is irrelevant, their change interval stands, or warranty is voided.
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Old 03-23-2020, 04:50 AM   #7
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I have no doubt dino oil will last 20K miles either. An oil analysis should be done any time OEM oil change interval is ignored though.
Cummins states the type oil is irrelevant, their change interval stands, or warranty is voided.
Feel free if you'd like, after 30 years of seeing the insides of engines I'll stick to what I know keeps them clean.
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Old 03-23-2020, 05:03 AM   #8
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Most RV's don't often get 150,000 miles on the odometer. My son in law, a certified diesel and gasoline engine mechanic, states emphatically that regular oil changes keep engines running smoother and longer. Although he prefers synthetic, either one will do well IF the oil is changed regularly and within the manufacturer's time/mileage specs.
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Old 03-23-2020, 09:10 AM   #9
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I went to 7500 or more on the gas engines years back with synthetic and the upgraded synthetic filter. Never an issue and we drove many to well over 100K. It was 43 miles to town so got the miles put on everything over time

On the diesels pretty much Dino or blend except for the 6.7's and went full synthetic and pushed the mileage up to 7500 or per the computer same as the gas

On the Cummins and JD's pretty much Dino due to the cost of a barrel or tote

Now that retirement has a lot less engines the Synthetic on sale is my chosen route however the Dino with the new packages is much better than what we used 20 years ago

We went the Synthetic route on the others due to the cold starting which was a huge plus
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Old 03-25-2020, 09:34 PM   #10
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Feel free if you'd like, after 30 years of seeing the insides of engines I'll stick to what I know keeps them clean.
I stick to mfgr recommendations. I have also seen Blackstone analysis of dino-oil that was still within specs at 20K or over. I never said I try to extend oil change intervals.
I did flush out a diesel once that was ran with the same oil for years. I used a 50/50 mix of kerosene and 30W oil, not only was the mixture in the drain pan black, the bottom was coated with gritty soot.
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Old 03-26-2020, 06:39 AM   #11
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I stick to mfgr recommendations. I have also seen Blackstone analysis of dino-oil that was still within specs at 20K or over. I never said I try to extend oil change intervals.
I did flush out a diesel once that was ran with the same oil for years. I used a 50/50 mix of kerosene and 30W oil, not only was the mixture in the drain pan black, the bottom was coated with gritty soot.
A manufacturer can't recommend something that didn't exist at the time the product was produced, oils have come a long way

Thank you for making my point with your statement about flushing

The question wasn't is regular oil good enough, it was is synthetic ok to use, and by all metrics it is a better oil. I have yet to ask you to use it, nor have I said it isn't good enough. Feel free to use what you like.
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Old Today, 05:25 AM   #12
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A manufacturer can't recommend something that didn't exist at the time the product was produced, oils have come a long way

That is not entirely correct. Our motorhome has the old 12 valve B-series Cummins. If you go to the Cummins Quickserve website, you will find that even the manual for this 26 year old engine has been updated, and recommendations/specifications for oil along with it.



For our engine, the recommendation is 15W40 conventional. They actually go so far as to say that synthetic is only recommended for arctic conditions.


All that said... synthetic oils are superior. The question is how much superior do you need to be on an engine that will already last hundreds of thousands of miles if properly cared for.



I experimented with T6 full synthetic in our motorhome a couple years ago. I immediately had oil leaking everywhere within a few hundred miles of the oil change. There were zero leaks prior. Not everyone has this experience... I ended up switching back to conventional, but the leaks did not go away until I tightened all the bolts on the timing cover and oil pan. It's almost like the synthetic caused the gaskets to shrink?



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Old Today, 07:10 AM   #13
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I have run Valvoline 5w-40 Premium Blue Full Synthetic in all my diesels. Cummins certified. 2008 to date 74000 miles.

Some of Rotella synthetics are dino oils with their molecules mechanically aligned not completely full synthetic.
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Old Today, 09:16 AM   #14
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I have run Valvoline 5w-40 Premium Blue Full Synthetic in all my diesels. Cummins certified. 2008 to date 74000 miles.

Some of Rotella synthetics are dino oils with their molecules mechanically aligned not completely full synthetic.
Ran the same when traveling and changing in my 6.7

Traded it at well over 100K and still ran like new, never an issue and it towed its entire life at near maximum weights
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