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Old 15th July 2014, 13:18   #1
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Default The importance of changing CNG Filters on time

If you think that CNG maintenance was only about changing the air filters, spark plugs and keeping the spark plug at just 1.0 mm, then you need to read this article for sure!

My car, a Wagon R is now 90,000 Kms. I am a maintenance freak. I had maintained the car as per the service booklet provided by Maruti. At around 40,000 kms of driving I had felt that my car’s CNG performance was not as good as it was when I had brought it. Back then there was just a 5% difference in performance when you switched from petrol to CNG. But at 40,000 the difference was about 20%, which was not a very happy experience.

At 90,000 the situation deteriorated even further. I asked Martuti Officials at the Maruti Workshop at Naraina, the biggest workshop of Maruti and they were clueless. I asked outside what we could do and everyone suggested to go to Maruti Workshop.

I thought there should be a separate manual for CNG maintenance too. My service booklet did not mention anything about it. So I googled it and downloaded a Wagon R CNG service manual from the net.

I was in for a big surprise!

It said two things:
CNG REDUCER FILTER CARTRIDGE WITH O RING TO BE REPLACED at 40,000!
CNG LOW PRESSURE FILTER CARTRIDGE WITH O RING TO BE REPLACED at 20,000, 40,000, 60,000, 80,000 and 1 lac Kms!


By that booklet I had skipped 4 low pressure replacements and one Reducer filter replacement! Just 20 days ago I saw the huge difference in cooling I achieved by cleaning my AC Filter (Below the Glove Box). I was on the verge of a major AC overhaul before I thought I would give the AC filter a try. I read a Team BHP article and followed the instructions and cleaned the filter first by shaking it and then with Arial detergent by dipping in a bucket. I let it dry for a full day (water should not go into the cooling duct was the precaution). And when I started the AC it was like my car was new! I saved 2500 in repairs I would have paid. So I knew what choked filters could do to performances.

I immediately called Maruti Workshop and asked why did they not change the filters in my car and didn’t even advice me to do it. The head of maintenance Mr. Sarkar apologized and asked me to come that day itself and said he will get this done.

It was surprising that such a big workshop had neglected service procedure and overlooked vital replacements. The cost of the entire replacement, I was told would be approximately Rs. 3000, which was not small by any yardstick.

The amount made me doubt if this was really required and if, after replacement, I would get any benefit by way of engine performance. But I was not too happy with the Wagon R’s CNG performance and decided to go ahead.

It turned out they had only one filter that day, the: CNG LOW PRESSURE FILTER CARTRIDGE WITH O RING. They were not aware of the part number of the other filter and promised they would do a complimentary replacement (no service or labour charge) and apologized for the two trips I would have to make instead of one.

Anyway I got this filter changed for Rs. 1676. This is the filter that should be changed every 20,000 kms but I think you can go for a replacement after 40,000, safely. I got the change at 90,000 kms! And when I drove the car, the effect was phenomenal! My car was like new. It was like the engine was finally able to breathe.

They gave me the replaced part and just to see how much choked it would be, I tried to open. It was a fused assembly and not a threaded assembly. So I had no option but to break it open with a hammer. My heart sank when I saw a very clean looking filter (steel and not paper like I had expected!). There was no dirt at all, unlike the AC filter which was choked hopelessly. I thought the increaser performance was my imagination only, or maybe they had tuned the car. But when I touched this steel filter, it was very oily! That intrigued me. Was oil a part of the filter mechanism? I wondered. It was simply unlikely because there was no oil in the casing I had broken. So maybe it was the oil that was causing the clogging, said my logic.

I decided to google again. I typed oil presence in CNG filter and the result was a link to a pdf. It gave me the shock of my life! Here is what it said:

Natural gas used for vehicular application and delivered from a CNG fueling station must be free of any solid material, water or oil. The heart of the natural gas fueling station is the compressor and most compressors require lubrication (oil). Over time, it is impossible to prevent some amount of the lubricant from leaking into the fuel stream. Specific equipment, called a coalescing filter, is designed to remove any liquid or solid contaminate in the high-pressure natural gas. They need to be installed downstream of the compression system, before the compressed natural gas enters the time-fill or high pressure storage system, as well as on-board the vehicle’s fuel system, to ensure that oil does not get into the on-board fuel storage cylinders and ultimately into the engine.

So the culprit in this case was not air but the compressor installed at CNG stations. The oil from compressor would invariably mix with CNG and get inside the filter and to some extent the engine too. The damage, the pdf said could be huge for the engine and even the CNG kit. It could damage the solenoids of the CNG kit too! So it was not just a matter of performance. It was a matter of protecting CNG kit and the engine that the CNG filters should be replaced periodically.

No where in the net is the complete finding mentioned, so I have taken pains to write this article. So guys it is not the CNG which will pull your engine down, it is the oil of the CNG station compressor that will take your car down, if you don’t change the filters regularly!

Without a second doubt, I got the second filter changed. I had to chase them for a week, constantly before they finally said they have the part in the store. I changed this part and the performance of my car is even better! This particular filter was open for me to see. It had a spring and paper/cloth filter and the paper was clogged with dirt and very smelly. I paid Rs. 1480 this time.

Part No. of the two filters:

CNG low pressure filter cartridge with O-Ring Part No. 15410 M78 L70

CNG REDUCER FILTER CARTRIDGE WITH O RING 15616M67L70

Conclusion
  • The car performance is greatly affected if these two CNG filters are not changed frequently
  • The engine can be damaged and you can be in for costly repairs if you don’t replace these filters
  • The CNG kit can be damaged due to oil short circuiting the solenoids.
  • Never trust any organization to do all the work for you. Organizations are made of mediocre people who may not have a passion for excellence. If you are very finicky about performance and maintenance, it would be good to double check with the manuals. In my case I had not received the CNG service manual but just the Petrol manual!

Last edited by Aditya : 16th July 2014 at 12:54. Reason: Editing spacing for better readability
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Old 15th July 2014, 14:10   #2
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Default re: The importance of changing CNG Filters on time

Dear Ravi

Very well written and informative review.

The filters needs to be changed at specified intervals.
The Wagon R CNG has two filters which the mechanics term as High Pass and Low Pass Filter.

In this service, (60K) they had checked the filters and found them satisfactory so the change was not done.

However, in my 40K service, both the filters were replaced at Rs. 16XX for High Pass and Rs. 1280/- for low pass filter.

The AC filter cleaning is a simple DIY and it is located behind the glove compartment and unscrewing a couple of screws will give you access.

Also, to help the car breathe better, the air filters needs to be replaced in every service rather than air cleaned in CNG. The main reason is that CNG being a lighter fuel needs a higher air intake compared to petrol. The filter, if clogged will immensely affect the performance(as told by the MASS advisor).
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Old 15th July 2014, 14:18   #3
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Default re: The importance of changing CNG Filters on time

@syravi:

Thanks a LOT for sharing your findings and research.
I am sure most of us had no clue about this.
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Old 15th July 2014, 21:00   #4
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Quote:
Originally Posted by arnabchak View Post
Dear Ravi

Very well written and informative review.

The filters needs to be changed at specified intervals.
The Wagon R CNG has two filters which the mechanics term as High Pass and Low Pass Filter.

In this service, (60K) they had checked the filters and found them satisfactory so the change was not done.

However, in my 40K service, both the filters were replaced at Rs. 16XX for High Pass and Rs. 1280/- for low pass filter.

The AC filter cleaning is a simple DIY and it is located behind the glove compartment and unscrewing a couple of screws will give you access.

Also, to help the car breathe better, the air filters needs to be replaced in every service rather than air cleaned in CNG. The main reason is that CNG being a lighter fuel needs a higher air intake compared to petrol. The filter, if clogged will immensely affect the performance(as told by the MASS advisor).
Thank you arnab. You were lucky you had passionate people inspecting your car CNG. I had to go by my instincts to get to the bottom of this.

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Originally Posted by bblost View Post
@syravi:

Thanks a LOT for sharing your findings and research.
I am sure most of us had no clue about this.
Thanks for appreciating!

Last edited by GTO : 16th July 2014 at 13:28. Reason: Merging back to back posts
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Old 15th July 2014, 21:16   #5
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Mod Note : There are several spelling & grammatical errors in your posts. This negatively affects the forum experience for other readers.

Kindly ensure that you proof-read your posts prior to submission. Also, it would be a good idea to use spell-checkers.

Last edited by GTO : 16th July 2014 at 13:27.
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Old 16th July 2014, 16:13   #6
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Is this filter present on sequential type cng kits as well ?
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Old 16th July 2014, 16:27   #7
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Default Re: The importance of changing CNG Filters on time

@syravi thank you for the detailed post. Just had my 2008 SX4 converted to CNG with a Lovato Kit 2 days back! I had researched about the maintenance that needs to be done after CNG conversion, but nowhere did I come across an informative article like this one. While I enjoy the new-found economy, will surely keep these intricacies at the back of my mind.
Cheers!
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Old 16th July 2014, 16:43   #8
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Default Re: The importance of changing CNG Filters on time

Wow, this is an interesting piece of information that you have shared over here.


But, what about people who fit aftermarket CNG kits? Can they source these filters locally? I guess this is one of the reason why lot of people complain that CNG cars lose out on power after a few years of usage.

Thank you for sharing!
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Old 16th July 2014, 17:25   #9
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Default Re: The importance of changing CNG Filters on time

I suppose this is limited to sequential kits. I drove my old WagonR F10D for over 1.5L km on a conventional CNG kit and I never changed anything like this. I doubt it had any such filters in the first place. The CNG mechanic also never mentioned about them over all the years I dealt with him.

I had no issues with my car for as long as I had it. Regular servicing kept it going for 2.75L km when I sold it off.
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Old 16th July 2014, 19:58   #10
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Quote:
Originally Posted by sumeethaldankar View Post
Is this filter present on sequential type cng kits as well ?
These filters are present in all kinds of kits. The wagon R factory fitted CNG kit is a sequential kit from Lovato

Quote:
Originally Posted by Shreyans_Jain View Post
I suppose this is limited to sequential kits. I drove my old WagonR F10D for over 1.5L km on a conventional CNG kit and I never changed anything like this. I doubt it had any such filters in the first place. The CNG mechanic also never mentioned about them over all the years I dealt with him.

I had no issues with my car for as long as I had it. Regular servicing kept it going for 2.75L km when I sold it off.
I have driven my car for about 90,000 kms with no intervention from trained mechanics of Maruti Naraina Workshop which is the largest in India. I would have driven another lac kms had I not been very sensitive to my car's performance. I faced a similar issue with the retrofitted CNG kit in my Maruti 800 at about 60,000 kms. No one had any solutions and I kept going from mechanic to mechanic with no solutions (the car experienced heavy vibrations on slow speeds and gear one and two). From the looks of it no one knows why these filters are there in the first place. It is just fit the kit and make quick bucks for most people. But there are obviously some who know these things should be replaced, just like a fellow bhpian had a mechanic who inspected and replaced the filters in his car.

Instead of assuming, it is best to find out. My gut feeling is that the filters have to be there to prevent engine from being damaged by oil from CNG compressor. It can also damage the kit.

Quote:
Originally Posted by SnS_12 View Post
Wow, this is an interesting piece of information that you have shared over here.


But, what about people who fit aftermarket CNG kits? Can they source these filters locally? I guess this is one of the reason why lot of people complain that CNG cars lose out on power after a few years of usage.

Thank you for sharing!
In all probability, the guys who sell these kits would not stock the filters otherwise they would have educated the people who install them. It is surprising, because it is a business opportunity for them too! But no one seems to care. It would be best to ask the guy who fitted the kit about the filters. If he doesnt have a clue then approach the company which made the kit about the filters through emails.

When the filter was not available even at Maruti Workshop I had asked around. The mechanic asked me if I had problems, I said just a little bit. He said, then why do you wish to change the filter!

In fact Mr. Sarkar too asked skeptically if the car was performing alright. Implying that if it is performing ok, then no need to change. But it is not about performance, the filter traps oil that can damage the engine or the kit. Otherwise the replacement would not have been mentioned in the schedule!

Last edited by SDP : 22nd July 2017 at 07:54. Reason: Merged. Also minor typo corrected
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Old 16th July 2014, 21:53   #11
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Default Re: The importance of changing CNG Filters on time

Quote:
Originally Posted by syravi View Post
Instead of assuming, it is best to find out. My gut feeling is that the filters have to be there to prevent engine from being damaged by oil from CNG compressor. It can also damage the kit.
I am just sharing my experience over an extended ownership period. Perhaps the F10D engine was more robust than the current K10.

Nonetheless, the point you make about compressor oil sneaking into the engine and potentially causing damage is logical. I am no expert in the construction of CNG kits but yes, this entire issue warrants further investigation.

You have raised a new and an important point that hardly anyone knows about.

Please share the WagonR CNG manual that you downloaded and mention the relevant page numbers.
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Old 17th July 2014, 11:04   #12
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Default Re: The importance of changing CNG Filters on time

Quote:
Originally Posted by syravi View Post
The wagon R factory fitted CNG kit is a sequential kit from Lovato
I believe the WR kits are sequential kits of Venturi and not Lovato.
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Old 17th July 2014, 17:06   #13
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Default Re: The importance of changing CNG Filters on time

I recently bought a Celerio CNG, 3 weeks ago. @syravi - Reading your post has really enlightened the maintenance knowledge I had. Will definitely read the Celerio Manual and check for similar information.

Kindly update us about anything more that we must know about maintaining a CNG fueled Engine.

@arnabchak - My car is going for it's first service tomorrow. And will be going for it's second service in a couple of months. Must i change the Air filter so soon?

Last edited by Pratzgh1 : 17th July 2014 at 17:07.
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Old 17th July 2014, 18:06   #14
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Default Re: The importance of changing CNG Filters on time

@arnabchak - My car is going for it's first service tomorrow. And will be going for it's second service in a couple of months. Must i change the Air filter so soon?[/quote]

HI

The air filter need not be changed in the first service or 1000 kms whichever is earlier.

However, do ask the advisor to take it out and air clean it. It needs to be replaced in your 2nd service though.
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Old 17th July 2014, 18:54   #15
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Quote:
Originally Posted by syravi View Post
I saw the huge difference in cooling I achieved by cleaning my AC Filter (Below the Glove Box). I was on the verge of a major AC overhaul before I thought I would give the AC filter a try. I read a Team BHP article and followed the instructions and cleaned the filter
[*]The CNG kit can be damaged due to oil short circuiting the solenoids.[*]Never trust any organization to do all the work for you. Organizations are made of mediocre people who may not have a passion for excellence. If you are very finicky about performance and maintenance, it would be good to double check with the manuals. In my case I had not received the CNG service manual but just the Petrol manual![/list]
Hi syravi,

I own a Wagon R K Series , Jan 2011 Vxi.Please share the process or thread from team-bhp to clean the AC filter.One problem which is bugging me on and off is the changeover from Petrol to CNG.Sometimes it does not change to CNG even after the cylinder is full and one day I wanted to rectify this issue, but after driving about 10 kms and in frustration I speed up the car on a mini speed breaker near Geeta Colony by pass road while coming from the Kashmere gate.That very moment when my car was crossing the speed breaker the car shifted to CNG. I particularly notice a sound coming from the right side of the engine bay, and it feels as if something is hitting continuously a hollow water mug . and it only comes when the car refuse to shift to CNG.

I really feel that there should be some specialized mechanics for the CNG cars but alas, everyone seems to just interested in fitting the kit and forgetting the maintenance part.

Please help me if out in this case if you have faced this issue of car refusing to shift to CNG and making weird sound as explained above in this post.
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