This may be a very noob question to ask. But I recently got this car and was used with 92 octane petrol. However, to my negligence I overlooked the user manual which states to include 95 octane petrol.
My question is, will it cause a problem if I fill the tank with 95 octane while it is quarter full with 92 octane petrol?
I did my on-line research and returned empty handed.
Mixing 95 octane gasoline with 92 is perfectly fine. In fact, this is what many gas stations do in order to offer their mid-grade product. For example, many gas stations in the United States offer 87, 89, and 91 octane gasoline. The 89 octane gasoline is a 50-50 mix of 87 and 91 octane gasoline. Mixing grades of gasoline will not harm your engine as long as the mix calculates overall to satisfy the manufacturer's minimum octane specifications.
To answer your question directly, adding the 95 to the 92 in your tank will not cause any real problems, in the short term. Once you have used the tank full you can carry on filling up with the recommended 95. Modern engine ECU programming will adjust the timing of your engine, knock sensors, to minimise or prevent engine 'pinking' caused by the lower octane fuel. Pinking can and will cause engine damage, and can be identified by a rattling from the engine, especially under acceleration.
