No. You can switch oil brands at every oil change, and you can top up with a different brand, as long as the viscosity and spec match what your manual calls for.
The brand on the bottle matters much less than two things printed on it: the grade, like 0W-20, and the approvals, like API SP or dexos1.
Why mixing oil brands is safe
Oils that carry the same API and ILSAC licenses are built to the same minimum tests, so they can share a crankcase. The American Petroleum Institute's own motor oil guide says that if you have to mix brands, use the same viscosity grade and API service category to keep the performance.
Mobil, which has every reason to want you loyal, says Mobil 1 is fully compatible with conventional, semi-synthetic and other synthetic oils. Its only caveat is that mixing dilutes Mobil 1's performance.
So if you're a quart low and the gas station only has a different brand of the right grade, buy it. Rick's Free Auto Repair Advice puts it bluntly: even the wrong oil is better than low or no oil.
What actually has to match
Match the grade and the spec. Brand is optional.
What's on the bottle | Does it need to match? | Why |
|---|---|---|
Brand (Mobil 1, Castrol, Valvoline, store brand) | No | Licensed oils are compatible (API, Mobil) |
Viscosity grade (0W-20, 5W-30) | Yes | Your manual specifies it; API says keep it the same |
API service category (SP) and ILSAC (GF-6A, GF-6B) | Yes, or newer | API SP and GF-6 are backward compatible with older categories (Valvoline) |
Maker approval (GM dexos1, European specs) | Yes, if your manual lists one | The maker's spec may go beyond API |
Synthetic vs conventional | Ideally | Mixing is safe but dilutes the synthetic (Mobil, Rick's) |
A note on the newer codes. API SP and ILSAC GF-6 took effect on May 1, 2020, and both work in engines that called for older oils like SN (Valvoline). GF-6B is only for 0W-16 and wears a separate "shield" mark so it doesn't end up in engines that don't call for it.
GM's dexos1 Gen 3 is backward compatible with earlier dexos1 generations, according to GM's TechLink bulletin. If your manual names dexos1 or a European approval, buy oil that lists that approval on the label, whichever brand it is.
Switching brands at an oil change
Switching brands at a full oil change is the easiest case. The old oil comes out, so you're not mixing much at all.
Owners on Bob Is the Oil Guy argue about this regularly. Most say they switch brands with no problems, or buy whatever is on sale. A few report an engine using a bit more oil for an oil change or two after a switch, then settling down.
One poster there had a reasonable explanation for those cases. A more detergent oil can clean out deposits and expose a valve stem seal that was already leaking. That's an engine problem the new oil revealed, not one it caused.
If your engine already burns oil, keep an eye on the dipstick for the first 1,000 miles after a switch. Our engine symptom guides cover what to check if the level drops.
When mixing does matter
There are three cases where I'd be careful.
- Your car needs a maker approval. Topping up a dexos1 or European-spec engine with a plain API oil is fine for a quart in a pinch. Don't run a full fill of it, and change back at the next service.
- You run a full synthetic for a reason. Rick's notes that adding conventional to synthetic dilutes the benefits. On a turbo engine or a long interval, top up with synthetic.
- The grade is different. A quart of 10W-40 in a 0W-20 engine shifts the whole fill. Rick's advises changing the oil sooner if you had to mix grades or specs in an emergency.
Warranty is worth a line too. Mobil says Mobil 1 won't void a new-car warranty where API-certified oil is recommended. What protects your warranty is using oil that meets the manual's spec and keeping receipts.
What to do today
- Open your owner's manual and write down the viscosity grade and any approval it lists, like API SP, GF-6A or dexos1.
- Keep a quart of a matching oil in the trunk. Any brand that lists those specs works.
- If you've already mixed in a different grade or a non-approved oil, plan an oil change sooner than usual.
- After switching brands, check the dipstick a couple of times over the first 1,000 miles.
Common questions
Is it bad to mix different brands of oil?
No, if they share the same viscosity and API category. The API guide says that's what to match when mixing brands.
Is it bad to switch oil brands every oil change?
No. Licensed oils meet the same standards, and most owners on Bob Is the Oil Guy report switching freely without problems.
Can I mix synthetic and conventional oil?
Yes. Mobil says Mobil 1 is fully compatible with conventional and semi-synthetic oils, though mixing reduces the synthetic's advantages.
Can switching oil brands cause leaks or oil burning?
It shouldn't cause them. Some owners report a short-lived rise in oil use after a switch, often on engines with existing wear that a fresh, detergent oil exposed.
Does it matter if I use a store brand oil?
Not if it carries the API donut and starburst or shield, and the grade and approvals your manual lists. Those marks are what count.
More oil and fluid guides are in our oils and fluids section.
Sources
- API: Motor Oil Guide (EOLCS)
- Mobil: Mobil 1 FAQs
- Valvoline: What is GF-6?
- GM TechLink: Next Generation dexos1 Gen 3 Engine Oil Now Available
- Rick's Free Auto Repair Advice: Can you mix motor oil brands
- Bob Is the Oil Guy forum: Any Harm in Switching Oil Brands?
Featured image: Man pulling oil dipstick to check engine oil level by Ivan Radic, CC BY 2.0. Source
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