We’ve covered both diesel and petrol injector cleaners on Parkers, but you might be wondering what engine oil additives are. Essentially, they’re compounds that help improve the lubrication of your engine oil.
A whole range of additives are out there. From anti-oxidants which fight against corrosion and sludge to viscosity index modifiers, which stop oil from thinning out too much at higher temperatures. Oil additives come in all sorts of forms and many are combined to tackle a number of things.
One useful thing worth noting is that synthetic engine oils are made up using a load of these additives. This is why the performance and durability of synthetic oils is vastly improved over conventional base products. They’re also quite beneficial to engines which have covered many miles, which means that lots of synthetic oils are useful as high-mileage engine oils.
The best engine oil additives at a glance:
Still, we understand that a lot of people will trust their local garages to service their cars and use whatever suitable oil is on site. This can mean that a load of cars aren’t using synthetic oil, so the room for adding in oil additives is quite large. Whether your car runs 5W-30 or 10W-40 engine oil, or many others, we’ve created a shortlist of the best ones you can buy to help your engine operate healthily.
The best oil additives
Editor's pick
It helps provide extra protection against excessive heat and reduces carbon deposits. This helps keep an engine running cleanly and smoothly while simultaneously reduces oil consumption. It's a great all-rounder as it can benefit high mileage engines, help reduce engine noise, assist with cold temperature protection and help improve the performance of engines with a poor maintenance history.
Pros
- Provides layers of protection for your engine
- Helps reduce oil consumption
Cons
- Petrol and diesel bottles are separate
Best oil additive for preventing oxidisation
It's recommended for petrol and diesel engines and protects against high oil consumption but low oil pressure and compression.
Pros
- Helps add a layer of protection with older engines
- Combats oxidisation and ensures strong lubrication
Cons
- Isn't as effective as synthetic oils
Best oil additive for treating tappet noise
Rrp: $14.09
Rrp: $14.09
It's important to note that after adding, you should run your car's engine until it's at the warm operating temperature to bed in the additive.
Pros
- Helps prevent tappet noise
- Can be used in all petrol and diesel engines
Cons
- Needs a little time to bed in
Best oil additive for protecting seals
Rrp: $20.00
Rrp: $20.00
While this oil stabiliser is advertised to stop leaks anywhere from your engine to the differential, it won't stop an oil leak caused by a perished seal that desperately needs replacing. Think of it as a preventative measure that helps prolong your engine's life.
Pros
- Effective at maintaining an engine's health
- Quantity is generous
Cons
- Doesn't contain many additional additives to improve performance
The best engine oil additive
One bottle of this additive can treat four to six litres of oil, and it can be used for both petrol and diesel engines as well as converted LPG engines.
Pros
- Useful for petrol, diesel, LPG and hybrid engines
- Helps improve engine cleanliness and smoothness
- Suitable for four to six litres of oil
Cons
- Isn't as comprehensive as other additives
The best additive for oil circulation
It helps to improve contact lubrication as well as keeping the oil circuit itself clean. You get 400ml of the additive, which isn't as much as other additives on the market, but it should be enough to treat an average-sized engine.
Pros
- Helps make the engine run more smoothly
- Cleans up areas of the engine where deposits build up
- Suitable for both petrol and diesel engines
Cons
- Isn't quite as comprehensive as others
The best oil additive for diesel engines
It's designed for regular use and helps remove harmful carbon deposits as well as reduce oil consumption. In turn, the additive will provide a smoother running engine as well as a cleaner one that'll likely last longer than an untreated diesel engine.
Pros
- Ideal for use in regularly-used diesel engines
- Helps clean up carbon deposits
- Contributes to reducing oil consumiption
Cons
- Don't expect a massive difference in oil consumption
Things to consider with oil additives
If my car runs synthetic oil, can I still use oil additives?
The simple answer is: it might not work as effectively – largely because synthetic oil makes an engine quite clean anyway. Fully synthetic oil is made of additives that help with the same things that sole oil additives are designed to do. Plus, synthetic oils have a habit of separating the sole additives rather than mixing the stuff in. You will have better luck if your car is running part-synthetic or fully conventional engine oils. Synthetic engine oils use a load of additives, so it’s always best to check before you buy.
Do oil additives really stop leaks?
The purpose of some of these additives is to help reduce the thinness of engine oil at high temperatures. Thin, hot oil leaks out of seals more easily than when it’s colder and thicker, so they can help reduce or even stop leaks, depending on the overall conditions. Some additives even work in gearbox oils and even oils found in differentials. But these tend to be more specialist.
But our advice is that they’re not sealants to perished seals or O-rings, so if you do notice a leak coming from your engine or gearbox, it will probably need a very worn-out part replacing. The job of the additives is to act as preventative measures. But it can never replace the necessity of changing your engine oil.
Are oil additives good for diesel engines?
Yes, they can be especially good to diesel engines simply because such engines have a tendency to build up slightly more carbon deposits than their petrol counterparts. Fuel system additives and engine oil additives are therefore a very good idea to keeping a diesel engine clean and healthy.
How to use engine oil additives
The key is to use oil additives as they’re designed; following the instructions accurately and applying it as the manufacturer intended. Adding in too much can have an effect on the viscosity of the oil itself, causing it to become either too thin or too thick. This can inevitably lead to engine damage thanks to bad lubrication.
How we choose
All of these engine oil additives have been hand-selected by our team of experts who have spent hours investigating and researching engine oil additives to make it easier for you to find the very best, and we’d never recommend a product we don’t believe in.
Where possible, we also test and share the latest and best products you should know about.
Aaron Hussain is a commercial content writer at Bauer Media writing for Parkers and CAR. He is obsessed with classic cars and anything with a fascinating story to tell.
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Just so you know, while we may receive a commission or other compensation from the links on this page, we never allow this to influence product selections – read why you should trust us
Just so you know, we may receive a commission or other compensation from the links on this website - read why you should trust us.
