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#4754096 - 05/11/18 10:58 AM Cummins N14 5W40 vs 15W40
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
I have a 1999 Monaco Signature 45í Class A. The motor is a Cummins N14. Just added a FS2500 bypass filter plus the factory Fleetguard FF filter. I havenít filled it with oil yet, but want to run synthetic and do EOC. Any issues with running 5W40?

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#4754105 - 05/11/18 11:08 AM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
beanoil Offline


Registered: 10/17/04
Posts: 2928
Loc: Midwest, Illinois
Probably not, but in Arizona, no need to. The 15w40 would be just fine.
There is no advantage to synthetic unless the conditions call for it. Temperatures or extended drains, maybe, but there are many, many UOA that prove that a conventional will do just as well as a full synthetic, depending on application.
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#4754121 - 05/11/18 11:21 AM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
A_Harman Offline


Registered: 10/01/10
Posts: 6891
Loc: Michigan
Just run 15w40. Valvoline Premium Blue Classic if it's still available. Or Mobil Delvac MX.
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#4754128 - 05/11/18 11:29 AM Re: Cummins N14 5W40 vs 15W40 [Re: A_Harman]
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
Neither of those are available in my town. My only synthetic option is the Rotella T6 5W-40

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#4754129 - 05/11/18 11:32 AM Re: Cummins N14 5W40 vs 15W40 [Re: A_Harman]
krismoriah72 Offline


Registered: 02/16/09
Posts: 1485
Loc: wv
Many millions of miles logged on the old N14 engines using nothing but conventional 15w40. Spend the money on clean air filters and clean fuel filters as well as coolant.

How much of an extended drain do you want? 10000 miles is the normal change interval.

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#4754149 - 05/11/18 12:01 PM Re: Cummins N14 5W40 vs 15W40 [Re: krismoriah72]
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
My plan was to go as long as possible using analysis. I figure with the bypass filter I should be able to easily go 20,000 miles. That was based on my reading regarding synthetics since they have a higher TBN

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#4754172 - 05/11/18 12:18 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
krismoriah72 Offline


Registered: 02/16/09
Posts: 1485
Loc: wv
Originally Posted By: offtosleep
My plan was to go as long as possible using analysis. I figure with the bypass filter I should be able to easily go 20,000 miles. That was based on my reading regarding synthetics since they have a higher TBN


Rotella T4 15w40 TBN is 10.27 http://pqiadata.org/Shell_Rotella_T4_15W40_4192017.html

Delvac 15w40 TBN is 11.0 http://www.pqiamerica.com/June%202014/ExmoDelvac13001540.htm


Rotella T6 5w40 TBN is 10.94 http://www.pqiamerica.com/June%202014/shellrotellat6.htm

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#4754185 - 05/11/18 12:41 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
jayg Offline


Registered: 10/04/12
Posts: 1189
Loc: Rabbit Creek, Alaska
Higher starting TBN doesn't necessarily mean it lasts longer though. TBN can drop faster or slower depending on oil and conditions.


If your only synthetic option is T6 in 5w40 then run it if you are dead set on extended drains. You don't need it for the winter weather starting obviously but I would feel more comfortable with the synthetic going 20k miles with the bypass filter setup.
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#4754194 - 05/11/18 12:55 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
racin4ds Offline


Registered: 05/07/10
Posts: 878
Loc: Ocala, Florida
If you're attempting extended drain intervals then yes you should use synthetic, and you should being that you've went to the expense and trouble to install a bypass filter setup.How many gallons of oil does the N14 hold?

I'm sure that ol Cummins will love the Rotella 5W40 either way.
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#4754195 - 05/11/18 12:59 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
Chris142 Offline


Registered: 06/05/03
Posts: 16678
Loc: Deplorable in apple valley, ca
Exactly how many miles are you thinking of running the oil? Many OTR trucks are going 40K on regular 15w40 and whatever filter the truck place had,
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#4754276 - 05/11/18 02:27 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
CT8 Offline


Registered: 10/09/14
Posts: 10730
Loc: Idaho
The only advantage the 5w- will buy you is below freezing starts. If you can use the starting advantage then run the syn.
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#4754345 - 05/11/18 04:05 PM Re: Cummins N14 5W40 vs 15W40 [Re: racin4ds]
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
I canít find anyone who has run the 5W40 in that engine, hence my concerns. The manual calls for 14 gallons.

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#4754347 - 05/11/18 04:06 PM Re: Cummins N14 5W40 vs 15W40 [Re: CT8]
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
Despite being in Arizona, I donít live at the lower elevations. We were freezing up until about a week ago. I live at 8000 FT ASL

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#4754350 - 05/11/18 04:09 PM Re: Cummins N14 5W40 vs 15W40 [Re: Chris142]
offtosleep Offline


Registered: 07/06/16
Posts: 6
Loc: Arizona
Iíd love to go that long! I think with UOA and the bypass filter, Iím hopeful. I hate wasting good oil just because itís been. Year. I donít think Iíll put more than 20k per year anyway. Mostly just hate wasting 14 gallons of oil when I donít need to

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#4754443 - 05/11/18 06:48 PM Re: Cummins N14 5W40 vs 15W40 [Re: offtosleep]
clinebarger Online   content


Registered: 12/19/13
Posts: 1834
Loc: Fort Worth, Texas
Originally Posted By: offtosleep
I canít find anyone who has run the 5W40 in that engine, hence my concerns. The manual calls for 14 gallons.


A lot of people have ran 5w40 HDEO in their N-14's, 350 engine hours should be easy to do with just about any good quality HDEO......That's a lot of run time for a recreational vehicle!!
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