Can you mix regular petrol and premium petrol?
Regular petrol and Premium petrol
Yes, this is fine
Yes. They blend, and the tank ends up somewhere between the two octane ratings.
What actually happens
Octane rating is a measure of resistance to knock, and mixing two grades gives an intermediate rating in proportion. A car specified for premium running on a mixture will retard its ignition timing slightly and lose a little power; a car specified for regular gains nothing at all from premium. Diesel in a petrol tank, or the reverse, is an entirely different question and a serious one.
What to do instead
Use whatever the fuel filler flap specifies. Higher octane than required buys nothing.
Vehicle fluids
| Combination | Verdict | Why |
|---|---|---|
| One engine coolant and a different coolant type | Do not | No — not across chemistries. The additives react and can gel. |
| DOT 3 brake fluid and dot 4 brake fluid | Fine | Yes. Both are glycol-based and fully miscible. |
| One engine oil and a different brand or grade | Fine | Yes. Any two oils meeting the same specification mix safely. |
| DOT 5 brake fluid and dot 4 brake fluid | Do not | No. DOT 5 is silicone and is not compatible with any glycol fluid. |
Common questions
- Can you mix regular petrol and premium petrol?
- Yes, this is fine. Yes. They blend, and the tank ends up somewhere between the two octane ratings.
- What happens if you do?
- Octane rating is a measure of resistance to knock, and mixing two grades gives an intermediate rating in proportion. A car specified for premium running on a mixture will retard its ignition timing slightly and lose a little power; a car specified for regular gains nothing at all from premium. Diesel in a petrol tank, or the reverse, is an entirely different question and a serious one.
- What should I do instead?
- Use whatever the fuel filler flap specifies. Higher octane than required buys nothing.
Related pages
- One engine coolant and a different coolant type No — it damages something or fails
- DOT 3 brake fluid and dot 4 brake fluid Yes, this is fine
- One engine oil and a different brand or grade Yes, this is fine
- DOT 5 brake fluid and dot 4 brake fluid No — it damages something or fails
- Bleach and ammonia Also produces a toxic gas
- Bleach and vinegar Also produces a toxic gas
- Bleach and toilet cleaner Also produces a toxic gas
- Bleach and rubbing alcohol Also produces a toxic gas
- Hazard symbols What the pictogram on the bottle actually requires
Sources
- Official vendor product documentation — At One Place