You see Waleed, even if you change your engine oil after 50,000 kilometers (yes, you read it right, fifty thousand kilometers) you engine will never come out of your car and tell you to change the oil.
What are you expecting from it? To start crying "Hey change the oil I have had enough?"
I have basically grown up in an Air Base. I myself am not an engineer, but I have many many friends who are officer's in PAF and are engineers and my father being someone who has worked on Aero Planes himself, I feel I'm pretty enlightened. Let me tell you my concept of CNG:
First of all (based on the link you posted) the whole argument is that CNG has a higher octane level. While that may be true, CNG too has a good amount of "OIL" level in it. Obviously you're not always buying CNG from the same guy. Feeding Oil to your engine is definitely like choking it.
Secondly, inspite of its high octane level (which is primary if you want it to burn) you should understand that its after all 'gas' its not liquid. No matter how high the octane level is, its many many times lower than petrol, because petrol is a liquid. Therefore one cubic centimeter of petrol (which is liquid) has much more octane than one cubic centimeter of CNG (because its all air).
The example the guy starting that topic is talking about is when both are compressed to a level that CNG becomes liquid (I assume).
The easiest way to know which fuel has more octane is to see how good a car is performing on each fuel. Obviously its petrol. Your car goes much faster in petrol than CNG reason is the bad quality of fuel.
My point was not that CNG has octane or doesn't have octane, my point was that since its 'gas' its dry. And therefore petrol provides a better lubrication and so we can change engine oil after sometime for this.
And then comes the question of misguiding people. The easiest way to know if CNG is good for your engine or not is this: Ask the people who are making cars.
Really very simple, isn't it? Do you think a single one of them will recommend you to put CNG in it? If no, why no? They are getting benefit out of it. Because as soon as you put CNG, they don't have to worry about your warranty. Why would they still not want you to put CNG?
Obviously because they make cars. They know how they work. They know what is harmful for it and what is not.
BUT IN SPITE OF ALL WHAT I HAVE SAID ABOVE You've missed a very clear point in the discussion:
No where did I say that I am in the favor of not running the car on CNG.
You can read my responses. I didn't say that anywhere. In fact, I wrote that I do not worry about people saying that you will destroy your engine. (read my first response in this thread).
You assumed it.
What we are discussing here is "should one really put CNG in Honda City 09/10 or not." And we are sharing our experience about it. We nowhere started the discussion that CNG is good or CNG is bad.
You can go through all of the above responses and you'll not find it.
Rather I was actually saying that the CNG kit is not free. And Honda City gives exceptional mileage on Petrol. So it doesn't really need a CNG kit. (that was my claim).
And our brother (vik_vik) was saying that 21Kmpl is not realistic. This is the discussion. Not that CNG is better or bad. BUT I DO THINK (atleast to my own self) that Petrol is way way better for the engine than CNG.
You get what you pay for. If you think you'll get something good by paying less, you're kidding. This doesn't happen. Specially not in the case of CNG.