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Old 04-15-2009, 12:27 AM   #2 (permalink)
Moderate your Moderation.
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Pasta - '96 Volkswagen Passat TDi
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Yes, temps are a factor, because engine intake temps will increase in warmer months. This means higher chance for detonation.

Assuming you have a 12 gallon tank, your fuel's octane rating on your change-over tank would have been approx:

2 x 93 = 186
10 x 87 = 870

870+186 = 1056
1056/12 = 88

So you'd have had 12 gallons of 88 octane fuel, approximately. Simple averaging is all you need to determine a mix of octane ratings.

Yes, it is possible that the ECU had to experience a re-learn with the new fuel. Being OBD-II compliant kind of makes it difficult to speculate without actually knowing how the ECU compensates for potential knock (detonation).
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