My mother was driving my car recently and decided to helpfully fill up the tank, unfortunately, she didn’t consult me first and topped it off with 87 octane instead of the 93-95 that the engine needs. How big an issue is this going to be?
(To make matters more complex, the tank was half-full with 93, so since she added another half of 87, does this mean the eventual blend/mix comes out to 90 octane?)
The Check Engine light might come on and you might hear engine knocking. The computer will compensate for it but it’s limited in how much it can do that. If you’re super worried you can take it to a shop and get the tank drained.
Or you can just drive real easy until you use some of it up. If you go that route, drive off about 1/4 of the tank then top up with the correct octane, repeat until you think the lower octane stuff has been used up.
Yes it does. The engine computer should detect premature ignition and dynamically detune the engine to avoid knocking with the effect of reducing output and efficiency.
Just fill up with high octane when it’s half full a couple of times.
What does ‘real easy’ entail - that by driving slowly, it’s better for the engine than if I drive fast?
It basically just means drive a little less than “normal.” You don’t have to drive Miss Daisy, but definitely don’t go all Fast & Furious on it. Just keep it around the speed limit and no drag racing off the line, is all. It will probably noticeably object if you push it too hard.
Ah thanks.
The computers are smart in newer cars–even my '02 Subaru with the H-6 engine prefers 92 octane but will cope with 87, just with a bit less oomph and the mileage will be less. And yeah, knocking can be an issue, especially in hot weather and long drives.
Lower octane gas is more susceptible to preignition. So putting 87 octane into the gas tank might cause preignition.
Fortunately your engine has a knock sensor. It listens for knocking (preignition). If it hears knocking, it will slowly change the timing just until the knocking goes away. Of course, this also means the engine will not be operating at peak performance. Putting 93 octane back into the tank will make it go back to optimal timing.
This. Basically modern engines since the 1980s or so have knock and ping sensors that detect the effects of too-low octane gas (knocking and pinging), and change the ignition timing to diminish or eliminate it.
Trouble is, that makes your engine both less powerful and less efficient, so it’ll likely burn more gas and be sluggish relative to if you’re running normal 93 octane gas.
But it won’t hurt anything.
Has anybody tried octane booster?
I know @FinsToTheLeft already answered this, but I wanted to add that this is exactly how gas stations that had three different octanes would handle it. The middle option would just mix the two.
I’d also say I’m not 100% sure that you’ll get 90 octane, but the mixture will be somewhere in between.
Finally, here’s an article about your main question, in this context due to people getting the lower octane stuff due to the shortage:
https://www.charlotteobserver.com/news/state/north-carolina/article251384363.html
But if it’s out of range, it voids your new car warranty. Pinging / pre-ignition can destroy an engine. I’m not a car person, I don’t know anything about modern engines, but even in the 00’s putting the wrong fuel into your new VW could destroy it.
Maybe… but I sort of doubt that a major US or Japanese manufacturer would actually make an engine that would incur damage if you ran commonly available gasoline in it. There are too many instances where you may be able to get 87 but not 93 for example.
That does sound like the sort of vehicular bitchiness VW might engage in though, considering that nearly every fluid in the car is some VW-specific one-off, and not the standard ones that the rest of Europe or the US uses. You have to have specific nearly impossible to get 50X.XX oil and some weird pink antifreeze, and special brake fluid, and so on… No using ATF+4, API SN/SP, and DOT 3/4, not for VW. I’ve got a '12 Passat, and it irritates the heck out of me how much more prissy the VW is versus the Dodge when it comes to fluids/filters/etc…
Exactly how bad this is depends on your engine. Some engines are better than others at knock detection and adjusting things to avoid damage.
For example, I have a Cadillac that is designed for 91 octane, but the manual says that it can run on 89 octane without damage. I know some other engines that aren’t so happy running on 89 though. Most engines these days will run on lower octane without damage, just at reduced efficiency. What is the year and make of your vehicle?
Regular and Mid-Grade are almost always 87 and 89 respectively in most areas, though 85 and 88 are used in some areas in the midwest. Premium varies a lot more though, and is 91 in some areas and 93 in others. Given that 93 isn’t even available in many areas, I strongly suspect that your vehicle is really designed to run on 91 or better.
Half a tank of 93 plus half a tank of 87 is probably about 90-ish and is also probably close enough to 91 that the engine will run fine. I wouldn’t worry too much about it, though I personally would also probably follow @DCnDC’s advice and put 93 in once I used up about 1/4 of the tank.
A couple of weeks ago I had a similar mishap with flex-fuel. I mistakenly filled up with flex-fuel in my non-flex engine, a 2017 Ford Edge. (I blame my sister, who called me just as I was selecting the fuel grade at the pump.) I didn’t realize what I was doing until the tank was full. As it was about 10% full when I started pumping, I now had a tank that was 90% flex.
I immediately called my mechanic, expecting to have my tank drained. But he told me to drive as usual, but fill up as soon as I had used up about 1/4 tank, and continue to do this four or five times. I did so and haven’t seen any adverse side effects. Mechanic said that the check engine light might come on, but that didn’t happen. He also told me not to make a habit of making this mistake.
Hopefully OP doesn’t mind a related question:
Does your car have some type of warning or label with the minimum octane rating? I’m just curious if high performance cars have some indication (besides the owner’s manual) to let a reasonably observant operator know the fuel requirements. I’ve never driven a high-performance car long enough to refuel it.
My car is labeled inside the fuel filler door “91 OCTANE OR HIGHER RECOMMEND, 87 MIN”
If not, or even if it does, I’d recommend consulting the owner manual in the glovebox for the full text, and pay attention to the exact wording they use. Most cars will say “XX octane recommended for best fuel economy,” in which case you can safely put in lower octane fuel. If it says “XX octane required”, then there may be an issue, and you’ll probably want to add octane booster and/or drive gently until you’ve burned off a large part of what’s in the tank, at which point you can refill with the right grade.
Continuing to blend the higher octane gas by topping off the tank a few times should clear the problem up.
There are not really 3 grades of gas available at the pump. There is no such thing as mid grade, it is blended at the pump by the pump with regular and premium grade gas. When you see a gasoline delivery truck it usually has only two tanks, a big one for regular and a smaller one for premium. Mid-grade is created at the pump.
Yes, it says 91 minimum. It’s a SmartCar. 93 or above is ideal but 91 is what the engine grudgingly accepts, I guess, given that some gas stations don’t offer 93 or 95.