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Old 07-25-2021, 10:13 PM   #1
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CNG to Diesel Conversion Cost?

Hello,

So I recently purchased two buses with CNG engines. I like CNG engines, but the only CNG station that was near me closed down and the closest one I have is 125 miles away, clearly not suitable.

They both have Cummins Westport ISL G engines, which share 80% of components with the diesel counterpart. For those of you that have experience, how much would it normally cost to completely convert a CNG bus to Diesel? I researched online and saw $5k-10$k, depending on if there's a diesel counterpart of the CNG engine.

Thanks!

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Old 07-25-2021, 11:11 PM   #2
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I can’t see any circumstance where that would be worthwhile. Just find a diesel bus you like and pay a premium to get what you want
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Old 07-25-2021, 11:17 PM   #3
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I canít see any circumstance where that would be worthwhile. Just find a diesel bus you like and pay a premium to get what you want
Actually, there is. Some CNG built buses are built with wider room then diesel buses, and also have space on the roof that can have solar panels installed.
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Old 07-26-2021, 06:18 AM   #4
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If you have Natural Gas available were you park the bus there are home compressors they sell for people with CNG cars. Pricey but it keep them full all the time while parked.
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Old 07-26-2021, 08:19 AM   #5
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Actually, there is. Some CNG built buses are built with wider room then diesel buses, and also have space on the roof that can have solar panels installed.

Well. All CNG buses that I know of have the tanks on the roof, and my bus is 102Ē wide, meaning that if it were even half an inch wider Iíd need a oversize permit.

But yeah, ISLs can be converted if the compression ratio is suitable, but not for $5k. The common rail injectors alone are over $5k. How about the ECM? Whoís going to program that?

Propane or gasoline are much lower hanging fruit for CNG conversion.

Even those are monumental tasks that can take from days to months to get going, and from months to eternity to get right, reliable and letís not talk about legal.
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Old 07-26-2021, 08:34 AM   #6
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IDK who told you 80% part compatibility, maybe if they count all the bolts individually. I think all 30+ oil pan bolts will interchange

5-10k wouldn't touch it if you had a shop do it.

You'll need an entire fuel system. Literally every component; tanks, hoses, filters, pumps, injectors, etc. That alone would eat your 5-10k budget. You'll need a compatible ecm and wire harness, and I believe the heads are proprietary to cng vs diesel, so you'll need a new head too. I know for sure the pistons are different, so you're swapping out 6 of those as well.

Yeah, you'll blow by 10k in just parts alone.

Hate to say it, but buying a diesel bus would be your best bet....... Or buy an ISL powered semi and swap everything over.

I think a different diesel bus would be cheaper.
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Old 07-26-2021, 09:09 AM   #7
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Quote:
Originally Posted by Bert06840 View Post
Well. All CNG buses that I know of have the tanks on the roof, and my bus is 102Ē wide, meaning that if it were even half an inch wider Iíd need a oversize permit.

But yeah, ISLs can be converted if the compression ratio is suitable, but not for $5k. The common rail injectors alone are over $5k. How about the ECM? Whoís going to program that?

Propane or gasoline are much lower hanging fruit for CNG conversion.

Even those are monumental tasks that can take from days to months to get going, and from months to eternity to get right, reliable and letís not talk about legal.

I looked at a school bus this weekend and the CNG tanks were under the bus behind the rear wheels.. it was a gasoline / CNG hybrid.. could run either.. turned about to be a RUST bucket so i ran away quick but the tanks were 18 years old on it so figured if I even wanted to run it on CNG id have had to change the tanks..
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Old 07-26-2021, 10:28 AM   #8
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You seem to have this all figured out so I'd say go for it. Give it the old college try!
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Old 07-26-2021, 10:50 AM   #9
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I know for sure the pistons are different, so you're swapping out 6 of those as well.
You seem to have access to Cummins information that I couldnít get to when I was looking for it a while ago. Might you share your sources?

I imagine that the crank would have to be different too, Iíd have a hard time believing youíd be able to efficiently double the compression ratio with a different head (or cut it in half since they started out with a 20:1 diesel.
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Old 07-26-2021, 10:54 AM   #10
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I looked at a school bus this weekend and the CNG tanks were under the bus behind the rear wheels.. it was a gasoline / CNG hybrid.. could run either.. turned about to be a RUST bucket so i ran away quick but the tanks were 18 years old on it so figured if I even wanted to run it on CNG id have had to change the tanks..

Oh, isnít that interesting! I canít imagine a use case for it though. Why would a district invest in such an oddball?

As I have said in other threads, I drove a CNG/gas bi-fuel Volvo when I was living in Europe, and there the sales argument was that you drive on NG when you can, and on gasoline when you canít (road trip or whatever). But that doesnít apply to school buses, or transit buses for that matter.
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Old 07-26-2021, 11:33 AM   #11
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im not sure where it came from.. it was for sale at a church and the church guy said they had never filled the CNG had only run it as a gasoline bus.. in rural kentucky so maybe there were gas wells near or that the school had access to.. once I stepped into the bus and the floor felt like I was walking on a gymnastics mat.. plus being able to see the ground in a couple places I knew that bus was not going with me so I didnt investigate any further.. besides some of the CNG manifolds appeared to go around the engine where A/C compressors would normally go.. that was deal killer #1 even before the floors were discovered.. no ability to have A/C == No Me




the only diesel to CNG conversions ive seen are permanent.. and are engines which are structurally different..
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Old 07-26-2021, 12:03 PM   #12
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Quote:
Originally Posted by Bert06840 View Post
You seem to have access to Cummins information that I couldnít get to when I was looking for it a while ago. Might you share your sources?

I imagine that the crank would have to be different too, Iíd have a hard time believing youíd be able to efficiently double the compression ratio with a different head (or cut it in half since they started out with a 20:1 diesel.
The stuff I said is based off memory.

We had one come in years ago that was low on compression and torched the pistons. IIRC the head was different, and the pistons had the mexican hat offset to be centered below the spark plug. As far as the crank was concerned, I'd assume they were the same as it's they're both the same displacement, but nothing is certain as I didn't look at that.

IIRC, compression ratio for diesel was 18:1, CNG was 12:1.

I clearly remember seeing the heads and pistons were obviously different. Diesel uses 24v, natural gas was 12v.

As far as my access to cummins stuff, I have a shop and we have a subscription to insite, quickserve, etc.

And I'm not sharing it either.

If you want close, you can buy clones/hacked versions of the software off the internet. I'm not commenting on the legality of such products, or if they're entirely safe to use either.

Or contact your local cummins software distributor and pay to play.
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Old 07-26-2021, 12:15 PM   #13
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Thanks all for your opinions. I recently found out that the closed location near me actually got relocated 3 miles away but someone forgot to update the info on CNG now 🤦*♂️.

So Diesel conversion, not worth the money. I've been reading up on CNG, apparently these engines don't break down as often and are much cheaper then diesel. The tanks on both these buses expire in 2031.

My next question: safety. One of my biggest concerns are the compression tanks on the roof, I've heard stories (and saw a video online) about how they can explode if they're damaged or not maintained properly. I have a Cummins shop nearby that can maintain the engine/tanks, but what are some safety tips you guys can recommend?
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Old 07-26-2021, 12:26 PM   #14
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Quote:
Originally Posted by Booyah45828 View Post
The stuff I said is based off memory.

We had one come in years ago that was low on compression and torched the pistons. IIRC the head was different, and the pistons had the mexican hat offset to be centered below the spark plug. As far as the crank was concerned, I'd assume they were the same as it's they're both the same displacement, but nothing is certain as I didn't look at that.

IIRC, compression ratio for diesel was 18:1, CNG was 12:1.

I clearly remember seeing the heads and pistons were obviously different. Diesel uses 24v, natural gas was 12v.

As far as my access to cummins stuff, I have a shop and we have a subscription to insite, quickserve, etc.

And I'm not sharing it either.

If you want close, you can buy clones/hacked versions of the software off the internet. I'm not commenting on the legality of such products, or if they're entirely safe to use either.

Or contact your local cummins software distributor and pay to play.

the stuff on the interwebs os the real deal esp for the older engines on our aschool busses.. the subscriptipon makes sense for the newest stuff but the 5.9 and 8.3 stuff for school busses? download it and and live on
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Old 07-26-2021, 12:53 PM   #15
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Originally Posted by cadillackid View Post
the stuff on the interwebs os the real deal esp for the older engines on our aschool busses.. the subscriptipon makes sense for the newest stuff but the 5.9 and 8.3 stuff for school busses? download it and and live on
We need the subscription to print RO's and do warranty work. I don't think that would fly if we didn't have the subscription, or if we were using an old version of insite.

But you're right, anything with a 5.9 or 8.3 can be diagnosed with earlier versions of insite. Both engines are 10 years or more, so old versions work fine with them. I think programming requires the latest version, though, because the files are internet based. I've never tried accessing incal with an old version of insite.

I guess if you have the disc image of the calibration file, you could use a hacked version of insite to reprogram it. I've never had the need to do so, so I've never done it.

Some of the mhh auto stuff is loaded with malware, that was my point of it being safe to use.
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Old 07-26-2021, 01:42 PM   #16
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I use burner machines for all the mhhauto stuff I use.. no internet access and no HDD share... virtual machine running inside a docker container
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Old 07-31-2021, 03:49 PM   #17
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I would consider an LPG conversion, that engine has spark ignition, not compression ignition like the diesel models. Its a ground up design for gasous type fuels.
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Old 07-31-2021, 08:34 PM   #18
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Quote:
Originally Posted by the7exp View Post
Thanks all for your opinions. I recently found out that the closed location near me actually got relocated 3 miles away but someone forgot to update the info on CNG now 🤦*♂️.

So Diesel conversion, not worth the money. I've been reading up on CNG, apparently these engines don't break down as often and are much cheaper then diesel. The tanks on both these buses expire in 2031.

My next question: safety. One of my biggest concerns are the compression tanks on the roof, I've heard stories (and saw a video online) about how they can explode if they're damaged or not maintained properly. I have a Cummins shop nearby that can maintain the engine/tanks, but what are some safety tips you guys can recommend?
Did a couple of years on the reliablity testing for the Cummins for Freightliner and among the many problems that we had were is that if you shut it off when hot it would vapor lock and get towed because it sure wouldn't start again, plus it was very short of power slow to accelerate and poor exhaust brake. Being a test truck ours probably didn't run 40% of the time ,the tanks were very sensitive to temperature and when they vented if you were not expecting it to be that loud it would make you think of changing your shorts. Even with the 2 saddle tanks and the stack behind the sleeper the range was under 400 miles.
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Old 08-01-2021, 12:17 AM   #19
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My next question: safety. One of my biggest concerns are the compression tanks on the roof, I've heard stories (and saw a video online) about how they can explode if they're damaged or not maintained properly. I have a Cummins shop nearby that can maintain the engine/tanks, but what are some safety tips you guys can recommend?
Iíve owned a couple propane trucks in the past and I know propane in many ways is safer than gasoline, the tanks are much stronger for one. So I would assume cng is also. If the tanks were exploding I donít think theyíd be installing them. Just donít drive into a low bridge, donít park in enclosed areas, donít paint the tanks anything but very light colors (Iíd stay with white) and donít over fill the tanks (propane is 80% full max so cng might be something similar. That should make it pretty safe.
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Old 08-01-2021, 03:08 AM   #20
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I would consider an LPG conversion, that engine has spark ignition, not compression ignition like the diesel models. Its a ground up design for gasous type fuels.

LPG or LNG?
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