Hey i have got cultus VXRI 2008 model. it gave me 17 km/L once when i checked cuz mostly i drive car on cng. Few days back i drive my car on petrol for 4 days. It gave me 14.5 km/L. i got the plugs checked they are in a good condition. The milage since i changed my plugs is 10,000km till now. What is average life of spark plugs ? After how many kilometers they should be changed.