Premium Gas; Minimum Octane?
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Joined: Sep 2025
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From: Illinois
2026 Mercedes-AMG GLC43 Coupe 2025 BMW X5 M60i 2005 Porsche 911 Turbo Cab 2023 Kia Sportage
Premium Gas; Minimum Octane?
Have a 2026 AMG GLC43 Coupe and have heard different recommendations for which Octane to use. MB says minimum of 91 while I've heard from others 89 would do. What experiences have you had using 87, 89, 91+...and what's the best route to keep running smoothly.
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Out Of Control!!
Joined: Nov 2018
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From: San Francisco Bay Area
2019 C63CS
Open the gas door flap and read the sticker. It clearly states 91 is the minimum. More information can be found in the owner's manual. 89 can be used in a pinch if at least 91 isn't available, but especially with higher power AMG engines, when doing so you must avoid high engine loads. No WOT or driving hard and refill with 91 as soon as possible before using high engine loads again. It's all about pressure. The highly compressed air/fuel mixture of turbo charged engines is more prone to pre-detonate if the octane rating of the fuel is too low, but a casual run to the grocery store on 89 isn't gonna be an issue. Problems occur if you try to use all the power the engine offers while running with less than 91.
Last edited by superswiss; Apr 27, 2026 at 11:46 AM.
Member
Joined: Mar 2017
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From: East Hampton NY
GLC300/GLC300C4
Back in the day when i use to lease and get a new car every 2 to 3 years i didn’t care what gas i used I would use 87 oct on a regular basis. Now that I keep my cars for 5-7+ years I run the required octane 😎
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From: SFV
2025 C300
Just my experience. I'm not sure if the engine timing was actually thrown off, but the sensors caught something for sure.
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From: Vermont
2023 GLC 300, 2021 VW ID4
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