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Redex Petrol System Cleaner is a fuel additive made to clean deposits from the fuel system and fuel injectors in petrol engines. I would treat it as a maintenance product rather than a fix for a serious engine fault. It can make sense if your car has an older or dirty fuel system, but you should not expect a dramatic MPG or performance change from a single dose.
Quick Answer
Redex Petrol System Cleaner can help clean deposits from the fuel system and fuel injectors in petrol engines. I would use it as a maintenance product, not as a repair for engine faults. The current dosage is 2.5ml per litre of petrol, and it is suitable for compatible petrol cars using E10 or E5 fuel.
What Is Redex Petrol System Cleaner?
Redex Petrol System Cleaner is a petrol fuel additive that you pour into the fuel tank. It is made to clean deposits that can build up in the fuel system and injectors over time.
Redex says the product is suitable for petrol engines, including hybrids, and can be used with E10 and E5 petrol. It also claims to help reduce emissions, restore performance and improve fuel efficiency.
I see it as a simple extra step in car maintenance. It does not replace an oil change, spark plug service, injector repair or proper engine diagnosis.
Does Redex Petrol System Cleaner Work?
Yes, it can help clean fuel-system deposits, but I would keep my expectations realistic.
Fuel injectors need to deliver petrol in a controlled way. Deposits can affect how well they do this. A fuel system cleaner is intended to remove some of that buildup and help the system work more efficiently.
The key point is the condition of the car.
If your fuel system has deposits that are affecting engine operation, you may notice a smoother idle, better throttle response or improved fuel economy after using a cleaner. If your engine is already clean and running well, the difference may be very small.
I would not expect Redex to suddenly add extra horsepower or give you a large MPG increase.
Real-world tests of fuel additives have also shown why fuel economy can be hard to judge. Traffic, road type, weather, driving style and tyre pressure can all change MPG, so a small difference cannot always be linked to the cleaner.
What can affect the result?
You may get more noticeable results when:
- The car has high mileage
- The fuel system has not had much maintenance
- Injectors have some deposit buildup
- The engine has become less smooth over time
- Fuel economy has dropped without another obvious cause
On the other hand, a cleaner is unlikely to solve a problem caused by a failed mechanical or electrical part.
What Does Redex Petrol System Cleaner Clean?
The main target is the fuel system, especially deposits around the fuel injectors.
During normal engine use, deposits can form as fuel passes through the system and burns inside the engine. Redex is made to help remove this buildup and keep the injectors cleaner.
That does not mean it cleans every part of the engine.
I would not use the phrase engine cleaner as if it means the product can remove all carbon, sludge or dirt from the whole engine. Its main job is fuel-system cleaning.
How to Use Redex Petrol System Cleaner
Using Redex Petrol System Cleaner is simple.
- Check that you have the petrol version.
- Check the dosage on the bottle.
- Add the correct amount to the fuel tank.
- Fill the tank or add the product around refuelling.
- Drive normally.
The current product information gives a mix ratio of 2.5ml of Redex per litre of petrol. A standard 125ml dose treats about 50 litres of fuel.
I would follow the dosage marks on the bottle rather than guessing.
Redex Petrol System Cleaner dosage
| Petrol in tank | Redex dose |
| 20 litres | 50ml |
| 25 litres | 62.5ml |
| 30 litres | 75ml |
| 40 litres | 100ml |
| 50 litres | 125ml |
For example, if you have around 25 litres of petrol in the tank, the 2.5ml-per-litre ratio gives you about 62.5ml of cleaner.
The bottle has dosage markings to make this easier.
Should you add Redex before or after filling up?
You can add Redex before or after filling the tank.
I prefer the simple approach of adding the correct dose around the time I fill the tank. Redex recommends adding it to a full tank to reduce the chance of overdosing.
The important part is getting the amount right for the fuel in the tank.
Can you put Redex in a half-full tank?
Yes, you can adjust the amount to match the fuel level.
For example, if you have 25 litres of petrol, use about 62.5ml based on the 2.5ml-per-litre ratio.
Do not simply pour a full 125ml dose into every tank regardless of how much fuel is present.
How Often Should You Use Redex Petrol System Cleaner?
The manufacturer recommends regular use and says the product can be used each time you fill up. Its guidance also suggests using it every other fill depending on the car and mileage.
I would not treat that as a rule that every petrol car needs a dose at every fill-up.
Your driving habits, mileage and vehicle condition matter.
If you are using Redex as part of normal fuel-system maintenance, following the bottle instructions is the safest approach. If you are trying it because your car has a running problem, I would focus on finding the cause rather than relying on repeated doses.
Can You Use Redex Petrol System Cleaner With E10?
Yes. Redex Petrol System Cleaner is made for use with E10 and E5 petrol in compatible petrol vehicles. The current formula also includes protection against corrosion linked to the higher ethanol content in E10.
E10 contains more ethanol than E5. Some older cars have restrictions on E10 use, so the cleaner does not change whether your particular vehicle can use E10.
If your car is not approved for E10, use the fuel recommended for your vehicle.
Can You Use Redex Petrol System Cleaner in a Hybrid?
Yes, the current petrol system cleaner is suitable for petrol hybrids.
The important point is that a hybrid with a petrol engine still has a petrol fuel system. The engine may switch on and off more often than a normal petrol car, but it still needs the correct fuel and maintenance.
I would still check your vehicle handbook if you are unsure about a specific additive.
Can Redex Help With Poor MPG?
It can help if dirty fuel injectors or deposits are contributing to poor engine efficiency.
But I would not use Redex as my first answer to every MPG problem.
A drop in fuel economy can come from many things, including:
- Low tyre pressure
- Short trips
- Heavy traffic
- Aggressive driving
- Poor wheel alignment
- Brake drag
- Faulty sensors
- Worn spark plugs
- Engine problems
- Fuel system faults
A cleaner cannot fix all of these.
If your MPG suddenly falls, I would look for the cause first.
Can Redex Help a Rough Idle?
It may help if fuel injector deposits are part of the problem.
A dirty injector can affect fuel delivery, which may contribute to poor engine running. Cleaning the fuel system can help in cases where deposits are causing the issue.
But rough idle has many possible causes.
For example, you could have a problem with:
- Spark plugs
- Ignition coils
- Air leaks
- Fuel pressure
- Sensors
- Throttle body
- Injectors
- Engine compression
So I would not keep adding fuel additive if the engine continues to run badly.
A persistent rough idle needs proper diagnosis.
What Redex Petrol System Cleaner Won’t Fix
This is one of the most important points to keep in mind.
Redex is a fuel additive. It is not a replacement for a mechanic or a failed engine component.
It will not repair:
- A failed fuel injector
- A bad spark plug
- A faulty ignition coil
- A damaged fuel pump
- A broken sensor
- A vacuum leak
- Low engine compression
- A damaged fuel line
- A serious mechanical engine fault
For example, if one injector has an electrical fault, putting cleaner in the fuel tank will not repair that fault.
I would use a fuel-system cleaner for cleaning and maintenance, not as a cure for a warning light or serious running problem.
Is Redex Petrol System Cleaner Safe?
When used according to the product instructions, Redex Petrol System Cleaner is intended for petrol engines and is compatible with E10 and E5 petrol in suitable vehicles.
The product information also says the cleaner has been tested at up to four times the recommended dosage without harm. I still would not use that as a reason to add extra. The correct dose is the better approach.
If you spill the product on your skin, wash the area with water. Also avoid unnecessary contact with paintwork and follow the safety information on the bottle.
Can You Use Petrol Redex in a Diesel?
No. I would use the cleaner made for your fuel type.
Petrol and diesel fuel systems work differently, and Redex uses different formulas for the two types of engines. The petrol cleaner is not a substitute for a diesel system cleaner.
If you drive a diesel car, use a product made for diesel fuel.
Is Redex Petrol System Cleaner Worth It?
I think it can be worth using as a low-cost maintenance product, especially if you have an older petrol car or suspect that deposits may be affecting the fuel system.
But I would not buy it expecting a dramatic change in every car.
If the engine already runs smoothly, gets normal fuel economy and has no signs of a fuel-system issue, you may notice little or nothing after one treatment.
If deposits are affecting the injectors, a cleaner has a better reason to be useful.
My main rule would be simple: use Redex as maintenance, not as a repair.
Redex Petrol System Cleaner vs Premium Petrol
These are two different ways of approaching fuel-system maintenance.
Premium petrol may contain additional detergent additives and can have a higher octane rating. Redex is a separate fuel additive that you mix with petrol in the tank.
I would not assume that one is automatically better.
If your main goal is cleaning the fuel system, a dedicated cleaner gives you a direct way to add a fuel-system treatment. If you want the benefits of higher-octane petrol, that is a different reason to choose premium fuel.
Your car’s fuel requirements should come first.
How Long Does Redex Petrol System Cleaner Take to Work?
Redex says the cleaner starts working as it moves through the fuel system.
That does not mean you should expect an instant change in how the engine feels.
If deposits are affecting the fuel system, the result may become more noticeable over continued use. If the engine does not have a deposit-related problem, you may not feel any difference at all.
I would avoid judging the product only by whether the car feels different after a few miles.
Can Redex Lower Emissions?
Cleaning deposits from the fuel system can help the engine use fuel more efficiently, and Redex markets its petrol system cleaner as a way to reduce emissions.
But I would not use it as a guarantee that a car will pass an MOT.
If your emissions are too high, there could be a deeper engine, fuel or exhaust problem that needs attention.
A fuel additive should not replace proper fault diagnosis or servicing.
Can You Use Redex With Premium Petrol?
Yes, Redex says its Petrol System Cleaner can be combined with premium fuel.
The question is whether you need both.
If your car runs correctly on standard petrol, I would compare the extra cost of premium fuel with the cost of the additive before deciding what makes sense for you.
The two products serve different purposes, so there is no simple rule that says you must choose one over the other.
Final Take on Redex Petrol System Cleaner
I would consider Redex Petrol System Cleaner a useful maintenance additive, but not a miracle cure.
Its main job is to help clean the petrol fuel system and injectors. It can make sense for older cars, higher-mileage vehicles or cars where deposits may be affecting smooth running or fuel efficiency.
The biggest mistake is expecting it to repair a mechanical problem.
If your car runs well, you may see little change. If deposits are affecting the fuel system, regular use may help keep it cleaner. The best approach is to use the correct dose, follow the bottle instructions and investigate any serious engine symptoms instead of trying to fix them with additives.
FAQs
Can I use Redex Petrol System Cleaner in an older petrol car?
Yes, provided the product is suitable for your engine. I would check the vehicle handbook and use the correct dosage for the amount of fuel in the tank.
Can I use Redex Petrol System Cleaner with E10?
Yes. The current petrol system cleaner is made for use with E10 and E5 petrol in compatible petrol vehicles.
Can I use Redex Petrol System Cleaner in a diesel car?
No. Use the Redex product made for diesel fuel instead.
Can Redex Petrol System Cleaner fix a misfire?
I would not rely on it for a misfire. A dirty injector can sometimes affect engine running, but a misfire can also come from spark plugs, ignition coils, sensors, fuel pressure or other faults.
Can Redex Petrol System Cleaner improve fuel economy?
It may help if fuel-system deposits are affecting engine efficiency. However, I would not expect a fixed MPG increase, and other factors can have a much bigger effect on fuel economy.
How much Redex Petrol System Cleaner should I use?
The current standard dosage is 2.5ml per litre of petrol. A 50-litre tank therefore needs about 125ml. Always check the dosage instructions on your bottle before adding it.
