CNG has become one of the most popular ways to buy a used car in Delhi. CNG cars made up 17.3% of used cars sold in Delhi, according to Cars24 data reported by Team-BHP, a share the report links to the city's age limits on diesel cars. Running costs are low and a CNG car is easy to sell on. But a CNG car carries one part a petrol car does not: a high-pressure gas cylinder with its own paperwork and its own expiry date. If you are looking at used cars in Delhi NCR, these six checks stop you paying for someone else's problem.
Why the Cylinder Now Decides Whether You Can Fill Up
Every CNG cylinder must be hydro-tested at a PESO-approved testing centre once every three years, under Rule 35(1) of the Gas Cylinder (Amended) Rules, 2025, as reported by Millennium Post. The test confirms the cylinder can still hold gas safely at high pressure.
That rule is now enforced at the pump. Indraprastha Gas Limited (IGL), which runs more than 1,000 CNG stations, has started refusing to refuel vehicles without a valid hydro-test certificate. At 10 stations, cameras read the number plate and check the cylinder's validity against the PESO online portal, and IGL plans to extend the system to all its stations. A used CNG car with an expired test is a car you cannot fill in Delhi until it is retested.
Check 1: The RC Must Say CNG
Open the RC, or use Hooter's RC details check, and look at the fuel type. A factory-fitted or legally retrofitted CNG car should show petrol/CNG. If the RC says petrol and the car has a cylinder in the boot, the kit was never endorsed by the RTO. That causes trouble with insurance claims, fitness checks and resale. Walk away, or ask the seller to get it regularised before you pay.
Match the cylinder number too. Every cylinder carries a serial number, and the kit and test papers list it. The number on the papers should match the one stamped on the cylinder in the car.
Check 2: The Hydro-Test Date
Ask for the latest hydro-test certificate and check its date. The test is due every three years, so a car whose cylinder was tested two and a half years ago will need a fresh test soon after you buy it. Factor in the cost and the time the car spends at the testing centre. If the seller cannot show a certificate, assume the test is due and price it in, or ask for it to be done before the sale.
Check 3: Factory-Fitted or Retrofitted Kit
Factory-fitted CNG cars, such as Maruti Suzuki's S-CNG models or Hyundai's factory CNG versions, come with the manufacturer's warranty and are calibrated for the engine. A retrofitted kit can work well too, but only if it is a type-approved kit installed by an authorised fitter and recorded on the RC. Ask for the fitment invoice and the kit's approval papers. A cheap, undocumented kit is the most common source of trouble in a used CNG car.
Check 4: Look and Smell for Leaks
Open the boot and look at the cylinder, its mounting brackets and the high-pressure pipe that runs under the car. Rust on the cylinder, a loose bracket or a pipe rubbing against the body are all warning signs. With the engine running on CNG, there should be no smell of gas in the cabin or the boot. If there is, stop the inspection there. A workshop can do a proper leak test in a few minutes, and it is worth paying for before you agree a price.
Check 5: Drive It on Both Fuels
A bi-fuel car should start on petrol and switch to CNG smoothly once the engine warms up. On the test drive, run on CNG for most of the distance and note any jerks, misfires or loss of pick-up on flyovers. Then switch back to petrol. If the car runs poorly on petrol, it may have been driven on CNG alone for years and the petrol side may need attention. A check-engine light on either fuel needs an explanation. Our Faridabad test drive checklist covers the rest of the drive.
Check 6: The Insurance Must Cover the Kit
The insurance policy should mention the CNG kit. Factory-fitted kits are usually covered as part of the car, while a retrofitted kit has to be declared to the insurer and added to the policy. If the kit is not on the policy, a claim involving it can be refused. After you buy, the policy also has to move into your name within 14 days. Our guide to used car insurance transfer explains how.
What a Used CNG Car Should Cost You
A CNG car usually costs more than the same model in petrol, because buyers pay for lower running costs. That premium is fair when the paperwork is clean and the cylinder has years left before its next test. It is not fair when the RC lacks the endorsement, the hydro-test is overdue or the kit is undocumented. Use each gap to negotiate, or let the car go.
Remember that the cylinder takes up boot space, so check that what is left suits you. And like every car in Delhi NCR, a CNG car needs a valid PUC certificate to buy fuel. Our guide to No PUC, No Fuel explains the rule.
A Used CNG Car Checklist
Confirm the RC shows CNG and the cylinder number matches the papers. Ask for a hydro-test certificate dated within the last three years. Get the kit invoice and approval papers for a retrofit. Check the cylinder, brackets and pipes, and smell for gas. Drive on both CNG and petrol. Make sure the insurance lists the kit.
For a shortlist, see our picks of the best CNG second hand cars under ₹5 lakh and under ₹10 lakh. When you are ready, browse used cars under ₹5 lakh and ask each seller for the hydro-test certificate before you visit.
Get the Hooter app for daily updates: Download the Hooter app to browse verified listings, track price changes and shortlist cars before you visit.
Frequently Asked Questions
How often does a CNG cylinder need a hydro-test?
Every three years, at a PESO-approved testing centre. Keep the certificate in the car, because IGL stations can refuse to refuel a vehicle without a valid one.
Can I buy a used CNG car if the RC says petrol?
It is best not to. It means the kit was never endorsed by the RTO, which can cause problems with insurance claims, fitness checks and resale.
Is a factory-fitted CNG car better than a retrofit?
Usually, because it comes with the maker's warranty and calibration. A retrofit is acceptable if the kit is type-approved, fitted by an authorised fitter and recorded on the RC.
Does car insurance cover the CNG kit?
Only if the policy lists it. Factory kits are normally included, while retrofitted kits must be declared to the insurer and added to the policy.
Do CNG cars need a PUC certificate?
Yes. CNG cars need a valid PUC certificate just like petrol and diesel cars, and fuel stations in Delhi NCR can refuse fuel without one.