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!