Getting my daughter ready to head back to school today. Took her 2015 VW Tiguan 2.0 TSi out to get washed and gassed up. Car runs on premium (91 octane). Got distracted at the gas station (Valero) and put about half a tank (say 9 gallons) of regular unleaded (87 octane) in the tank. I'm use to filling up my F150 with regular.....

Any reasons to be concerned?
Assume the car will probably not run as smooth/idle rough? She's not doing any autocrosses or drag racing. (I hope not...).

Is it worth putting in a bottle of octane booster from O'Reilly's in the tank?
Or just have her put premium back in when the tank is half empty?

Thx SW86

hypeiv said:

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It will be fine. I assume it has half a tank of 87 and half of 93? If so that mixes to 90 octane.

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X2

Knock Sensors will r e t a r d timing.

Thanks for the confirmation - Told her to drive it and let me know if it did anything weird. Made it up to BCS without any check engine lights, etc.

I put a tank of regular in a corvette a few months ago. Could not tell any difference. Would I be correct in assuming the knock sensors are only going to kick in close to full throttle?

Jack Boyett said:

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I put a tank of regular in a corvette a few months ago. Could not tell any difference. Would I be correct in assuming the knock sensors are only going to kick in close to full throttle?

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That is correct. Most the normal commuting miles are done and you'll not feel the difference.

FWIW, my sister who used to drive an M35 and now a XC90 has always used regular and never had any issues. All her driving is shuttling kiddos and running errands.

hypeiv said:

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Also we are blessed with good gas in Texas and have access to 93. In a lot of states 91 is the best, so mixing 87 and 93 of Texas gas is about the same as the best stuff you can get in a lot of states.

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Dont get me started on 85 octane in colorado

The Lost said:

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hypeiv said:

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Also we are blessed with good gas in Texas and have access to 93. In a lot of states 91 is the best, so mixing 87 and 93 of Texas gas is about the same as the best stuff you can get in a lot of states.

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Dont get me started on 85 octane in colorado

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You really don't need high octane at high altitudes, do you?

You can run 87 3 out of 4 fill ups without any real issues, though some cars will have decreased gas mileage and be a little underpowered. You will need to do more deeper fuel system cleaning but with everyone that puts 87 in their car because its cheaper, there shouldn't be any real long term damage.