How Serious Is It?
| Situation | Risk Level | Action |
|---|---|---|
| Wrong grade (e.g., 5W-30 instead of 0W-20) | Medium | Change at next service or sooner |
| Wrong spec (e.g., non-DPF oil in DPF car) | High | Change immediately |
| Mineral in a synthetic-required engine | Medium-High | Change within 1,000 miles |
| Petrol oil in a diesel engine | High | Change immediately (DPF risk) |
| Diesel oil in a petrol engine | Low-Medium | Change at next service |
What to Do
If you’ve used the wrong oil:
- Don’t panic — short-term use of the wrong oil rarely causes immediate damage.
- Identify what oil was used and what your car actually needs (use our oil finder).
- If the spec is wrong for a DPF diesel, change the oil as soon as possible.
- If just the grade is slightly off (e.g., 5W-30 vs 5W-40), change at the next service.
- If you’ve driven less than 100 miles on the wrong oil, a drain and refill is all that’s needed.
Frequently Asked Questions
Will the wrong oil void my warranty?
Potentially, if the manufacturer can show engine damage was caused by incorrect oil. Keep receipts showing the correct oil specification for all future services.
Can I mix different brands of engine oil?
Yes — mixing brands of the same grade and specification is fine. The oil industry uses compatible additive packages.
Can I mix 5W-30 and 5W-40?
In an emergency top-up, yes. The result will be approximately 5W-35. Change to the correct grade at the next service.
