---
title: "Can you mix them? Vehicle fluids"
description: "5 combinations under vehicle fluids, with what actually happens rather than a blanket rule about not mixing things."
url: https://atoneplace.net/can-you-mix/vehicle/
site: "At One Place"
---

# 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?](https://atoneplace.net/can-you-mix/engine-coolant-types/) — No — it damages something or fails
- [Can you mix dot 3 brake fluid and dot 4 brake fluid?](https://atoneplace.net/can-you-mix/dot3-and-dot4-brake-fluid/) — Yes, this is fine
- [Can you mix one engine oil and a different brand or grade?](https://atoneplace.net/can-you-mix/engine-oil-brands/) — Yes, this is fine
- [Can you mix regular petrol and premium petrol?](https://atoneplace.net/can-you-mix/petrol-grades/) — Yes, this is fine
- [Can you mix dot 5 brake fluid and dot 4 brake fluid?](https://atoneplace.net/can-you-mix/dot5-and-dot4-brake-fluid/) — No — it damages something or fails

## Related pages

- [Cleaning products](https://atoneplace.net/can-you-mix/cleaning/)
- [Around the house](https://atoneplace.net/can-you-mix/household/)
- [Paint, glue and materials](https://atoneplace.net/can-you-mix/diy/)