Mixing vehicle fluids
5 combinations under 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. |
| Regular petrol and premium petrol | Fine | Yes. They blend, and the tank ends up somewhere between the two octane ratings. |
| DOT 5 brake fluid and dot 4 brake fluid | Do not | No. DOT 5 is silicone and is not compatible with any glycol fluid. |
- Can you mix one engine coolant and a different coolant type? No — it damages something or fails
- Can you mix dot 3 brake fluid and dot 4 brake fluid? Yes, this is fine
- Can you mix one engine oil and a different brand or grade? Yes, this is fine
- Can you mix regular petrol and premium petrol? Yes, this is fine
- Can you mix dot 5 brake fluid and dot 4 brake fluid? No — it damages something or fails
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