Cummins Diesel to CNG conversion and Motor Oil

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I am new to the forum, my 1st post, but I work with buses, transportation & logistics fleets, and of course motor oil. In CA a lot of diesels are being converted to CNG. I am wondering since a lot of my fleets are slowly converting all of their engines to CNG, do they have to then buy 2 motor oils. One for the diesels and one for the CNG engines?

Would mobil delvac 1300 work in a CNG converted engine. I'm talking mostly about the big cummins diesel bus engines which have the Valvoline premium blue recommended stamp on the engine block. The CNG engines come back with that same stamp. Does that mean cummins recommends Valvoline Premium Blue on their CNG engines, or that they were too lazy to remove the stamp?

Any insight would be much appreciated because it seems like CNG is going to be the future no matter what, at least in Cali (emissions laws).

Thanks Guys
 
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It is a pretty big ordeal. Costs upwards of $15-20K USD per engine, and another 5 grand for the gas tank. plus the buses can't go nearly as far per tank. The only thing that everyone agrees on is it burns cleaner/is a cheaper fuel.

I have heard all kinds of conflicting information:
it's better/worse for your engine.
extended oil change intervals are recommended/never extend OCI.
Any 15w-40 diesel oil works/you need a "GEO" CNG oil.

Since these are not going to be dual fuel buses/trucks (phase out diesel entirely) I have heard that they have to add spark plugs to the diesel engines.

Also it burns much hotter than diesel so all the internals need to be treated, and this is why the oil breaks down faster.


I've seen the engines and they look like a regular cummins diesel. I figure since I don't have much choice in the matter I might as well get educated.

I know this is an alternative fuel, but it is a HDEO question so I hope i'm in the right section here and someone can enlighten me.
 
My professor has been using propane on his gas truck after it warms up, since the energy crisis of the 70's.... He said they always ran longer than the frame lasted in Mn/Nd and he just used any 5w30 at normal intervals.
 
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Welcome and thanks for posting. It sounds like you have a nice project on your hands. I am glad to hear anytime vehicles are using or being converted to CNG. From everything I have read it is the cleanest burning fossil fuel in existence. I am seriously considering the Honda Civic NGV since Clean Energy opened a CNG station just South of downtown Chicago. Plus, they are giving away a $3,000 gift card for CNG at their stations until the end of the year when you buy a Honda.

To answer your question, I am not 100% sure but..... I have been reading a LOT about CNG engines and conversions. The one thing I read over and over is CNG burns clean which reduces the contaminants and acidity of the oil. CNG engines (especially gas, not as much in diesels) are great candidates for extended OCIs.

If I were you, here is what I would do.

1. Find out who's conversion system is being used. You mentioned the vehicles use Cummins diesel engines so they are probably using Westport equipment. Contact Westport and see what they say. Cummins-Westport have a working agreement. Anybody who wants to learn more about CNG diesel take a look here. http://www.cumminswestport.com/

2. Have the oil analyzed (post results on this forum if you can!) and see what the results are. Keep extending the OCIs as you see fit.

If I had to guess, the engine oil won't change because of the CNG conversion but you should check. I think you will just get longer OCIs.

Out of curiosity do you know what kind of conversion technology is being installed? I know of two for diesels.

1. Full CNG conversion- Very little or no diesel fuel used in these engines. This conversion requires installation of spark plugs. I have also read Westport has created a fuel injector with a glow plug tip which creates ignition so the installation of plugs can be avoided since an ignitions system adds complexity, points of failure, and added maint. costs.

2. Bifuel- Runs on both and can be adjusted as desired. Uses some diesel fuel to create spark for ignition.

I would love to hear from more experienced people on this.
 
rk1407: Thanks for the reply. it is the Full CNG conversion with sparkplugs. I will definitely get UOA's because I am curious and I will need them. So when I do, you all will get the results as well. I will call cummins westport and see what they say.

Carwreck: Thanks. I have seen specific motor oils for CNG and I guess i'm trying to figure out if they are necessary or just recommended. but thanks for the link, I have not seen these specs yet.

CNG engine oil seems to have a lower TBN (no idea why) and lower sulfated ash (this makes sense to me) as well as higher VI (which also makes sense because of extra heat).

I just want to make sure that my motor oil will work in both bc I don't want drums of different oils yet.
 
Originally Posted By: djten4
CNG engine oil seems to have a lower TBN (no idea why) and lower sulfated ash (this makes sense to me) as well as higher VI (which also makes sense because of extra heat).


If I recall correctly, the lower TBN (and lower sulphated ash) is used because there are no fuel dilution issues with CNG or LPG. Whether or not switching to such an oil for a converted Cummins is advisable is another issue. Most of the CNG/LPG oils I've seen have been in lower viscosity PCMO grades, and that may not be optimal in a Cummins. In this case, I think you need some expert opinion. There are a few here who may have some ideas.
 
Originally Posted By: ARCOgraphite
Nothing to add, though I was unaware you could convert a diesel to CNG. Something to read up on.


I was at the Kansas State Fair a couple of months ago and they had an OTR semi truck set up to run on natural gas. They occasionally started it up and had it running. I asked the guy a couple of questions that I knew the answers to and a couple of questions that I did not. The first two questions: "How many places in our state is there CNG refueling stations?" and "What is the PSI in the fuel tanks?" He lowered his voice (so nobody else could hear him) when he answered: "None, but we will have some in the future" and "About 3200 PSI". You've got to remember that a propane tank has a little over 100 PSI and CNG is over 3000 PSI. I'm not so sure I would like to be involved in an accident with that much pressure, but I guess gasoline is extremely flammable also.
I also asked him who manufactured the engine in that particular truck and he couldn't answer that. It did look like a coil-over-plug diesel conversion, however.
 
i work in the natural gas compression business. Most of our compressor engines are CAT 3306 diesel conversions. we run CITGO 1740 oil in them, i do not know how it relates to specs. of HDEO we use on the street. i believe it's a straight 40w. we have some Aarow engines( no conversion) on some pump jacks that run HDEO 15-40. My 2011 Chevy 2500 with IMPCO CNG conversion still runs 5-30 engine oil as it is dual fuel. for alot more info. on CNG conversions go to www.cngnow.com. Cummins and Westport are maketing a new all NG engine called ISX12 G, spark ingnited engine. 12 liters, 450 HP, 1450 #ft.tq. to be installed in over the road trucks.
 
Originally Posted By: Garak
Originally Posted By: djten4
CNG engine oil seems to have a lower TBN (no idea why) and lower sulfated ash (this makes sense to me) as well as higher VI (which also makes sense because of extra heat).

If I recall correctly, the lower TBN (and lower sulphated ash) is used because there are no fuel dilution issues with CNG or LPG. Whether or not switching to such an oil for a converted Cummins is advisable is another issue. Most of the CNG/LPG oils I've seen have been in lower viscosity PCMO grades, and that may not be optimal in a Cummins.
Oh thanks for your opinion... Does it imply that in CNG-driven engines, HDEO engine oils are not be unsuitable because of higher ash levels ? Will the HDEO hurt in any way(s) ?
 
Originally Posted By: lilred67
i work in the natural gas compression business. Most of our compressor engines are CAT 3306 diesel conversions. we run CITGO 1740 oil in them, i do not know how it relates to specs. of HDEO we use on the street.
i believe it's a straight 40w. we have some Aarow engines( no conversion) on some pump jacks that run HDEO 15-40.
Are these 'Aarow engines' using natural gas as the fuel ???
 
Originally Posted By: fpracha
Oh thanks for your opinion... Does it imply that in CNG-driven engines, HDEO engine oils are not be unsuitable because of higher ash levels ? Will the HDEO hurt in any way(s) ?


From what I understand, it's more of a case of "less than optimal" rather than any real harm. I know for LPG vehicles, the taxi fleet used nothing bought normal PCMOs (rather than specific LPG/CNG lubes) without any longevity issues. The engines would routinely last into the hundreds of thousands of miles with no lube related issues. With the nature of LPG, sludge was certainly never an issue.

As we know, there are certain reasons for low SAPS oils in various applications. A CNG/LPG engine simply doesn't need the high TBN of most modern oils, much less some of the very high TBN oils available years ago.

Personally, I wouldn't sweat it. I would rather ensure that the oil meets the viscosity requirements of the engine first before worrying about getting a low TBN oil, unless, of course, someone else here with experience can show us differently.
 
Great info guys, this site is a huge resource. When I get the oil running in CNG engines i'll be sure to post the UOA's bc im sure people will be curious.
 
The entire fleet of service trucks at the natural gas utility company my father worked for were Dodge Ram D250s that had their 5.9 liter straight six Cummins engines converted to run on CNG once warmed up. I believe it was done by fogging CNG in the intake and drastically reducing the amount of diesel injected.

Some diesel was always injected even when 'running on CNG' to ignite the natural gas and work as a UCL. IIRC at idle they ran approximately 40% of the normal amount of diesel and the remainder of BTUs were supplied by natural gas - the mix leaned out the diesel percentage as RPMs increased. He borrowed one several times for government projects around the house. I recall them all having insane miles on them (450k+ miles) but running very well and never producing any visible smoke or soot at all except when starting on straight diesel. Switchover was handled by a simple rocker switch on the dashboard... once the truck was started and warmed up, you flipped it from D2 to CNG. Hot restarts were fine on CNG.

When the trucks were returned to the service center at night, they were hooked up to a CNG cascade filling system that would trickle fill the two tanks in the truck bed overnight to 3000 psi. The tanks were mounted one on top of the other, right behind the cab. Apparently oil changes were able to be extended quite a bit and some trucks in frequent use would go a month or more on a single tank of diesel.
 
I was the mechanical development engineer of the C-series natural gas engine when I was at Cummins in '94-'95. This was a turbocharged lean-burn engine with coil-on-plug ignition and throttle-body gas injection. When I first started testing these engines, it was freaky to be able to hear valvetrain noise because the natural gas combustion was silent. Descendents of this early C-series engine are now being produced by Cummins-Westport, but I see they have migrated to a stoichiometric combustion strategy.

Mechanical design changes that we made in converting from diesel to natgas were with the pistons, rings, valves, valve seats, and valve stem seals. The cylinder head was a production casting but was machined for a spark plug in place of a fuel injector. The oil that we used for development testing was Mobil Delvac Super-GEO 15w40, which was a low-ash oil. Spark ignition heavy duty engines require low or no ash oil to eliminate or reduce ash deposits in the combustion chamber that could cause preignition under high load conditions. IIRC, TBN's of gas engine oils don't need to be much over 6.0 to get long OCI's, but you should be doing UOA's to gage this for yourself. There are some gaseous fuel applications out there that require higher TBN if the gas has high concentrations of sulfur compounds, such as landfill gas or sour gas wells.

We also had a problem with high lifter wear on some engines when it turned out that another gas engine oil we had selected had insufficient ZDDP to provide wear protection for the flat tappets. The Delvac Super-GEO provided better wear protection. If your engine has rolling cam followers, this is probably not an issue.
 
A freind and former co-worker of mine works on a large fleet of cummins CNG busses. Low ash/low zinc is what the specs call for.

They run a bulk Chevron Delo 400 15w40 NG oil. They also utilize bypass filtration for extended drain intervals.

Quote:
Delo 400 NG SAE 15W-40
Featuring ISOSYN Technology, Delo 400 NG SAE 15W-40 is a new, premium oil for use in a wide range of modern compressed natural gas (CNG) and liquefied natural gas (LNG) engines. With OEM approvals from Cummins and Detroit Diesel, Delo 400 NG SAE 15W-40 protects CNG/LNG engines from sludge, valve and piston buildup, offers superior anti-wear performance and extends service life between oil drains. It’s specially formulated to improve performance while lowering operating cost in all medium and heavy-duty CNG/LNG-powered fleets.



I have some limited experiance with the CAT 3600 series gas engine and we used CAT NGEO for those applications. You can spec the CAT stuff out with a mobil product.

Here is the specs on the CAT stuff:

Typical Characteristics {A}
SAE Viscosity Grade SAE 40
Gravity, API 27.5
Flash Point, °C (ASTM D92) 265
Pour Point, °C (ASTM D97) -15
Viscosity cSt @ 40°C (ASTM D445) 130
Viscosity cSt @ 100°C (ASTM D445) 13.5
Viscosity Index (ASTM D567) 99
Sulfated Ash, % wt. (ASTM D874) 0.48
TBN, mg KoH/g (ASTM D2896) 6.2
Phosphorus, % wt. (Spectro or AA) 0.030
Calcium, % wt. (Spectro or AA) 0.125
{A} The values shown are typical values and should not be used as quality control parameters to either accept or reject product. Specifications are subject to change without notice.
 
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