Skip to content 
If you are choosing between Redex and STP diesel injector cleaner, both products are aimed at keeping a diesel fuel system clean, but they are not positioned in exactly the same way.
I would choose Redex when my main goal is general diesel fuel-system maintenance. If I specifically wanted an injector cleaner, I would lean towards STP because its product has a more direct focus on diesel injectors.
Quick Answer
Redex is the better fit for general diesel fuel-system maintenance, while STP is the better choice if your main goal is cleaning diesel injectors. Redex uses a flexible dose based on fuel volume, while STP uses a 200ml treatment for 50–60 litres of diesel. Neither product can repair a damaged injector.
Redex vs STP Diesel Injector Cleaner at a Glance
| Feature | Redex Diesel System Cleaner | STP Diesel Injector Cleaner |
| Main purpose | Diesel fuel-system cleaning | Diesel injector cleaning |
| Injector deposits | Yes | Yes |
| Fuel-system focus | Broader | More injector focused |
| Typical treatment | 2.5ml per litre | 200ml for 50–60 litres |
| Treatment interval | Follow product instructions | Every 3,000 miles |
| Common-rail diesel | Suitable for diesel engines | Suitable for DI, IDI and common-rail diesel engines |
| Best suited to | General fuel-system care | Injector-focused cleaning |
| Can repair injector damage? | No | No |
| My pick | General maintenance | Injector cleaning |
Redex Diesel System Cleaner
Redex Diesel System Cleaner is made to clean deposits from the diesel fuel system, including deposits around fuel injectors.
I see it as a general fuel-system cleaner rather than a product aimed at one specific injector fault.
Redex recommends a dose of 2.5ml per litre of diesel. For a 50-litre tank, that works out at 125ml.
The product is also sold in larger bottles, so one bottle can provide more than one treatment depending on the bottle size and fuel volume.
What is Redex used for?
Redex is used as a diesel fuel additive to help clean deposits in the fuel system.
Deposits can build up over time and affect fuel delivery and engine performance. Cleaning these deposits may help the fuel system work as intended.
I would see it as a maintenance product rather than a repair product.
Why would I choose Redex?
I would choose Redex if I wanted a simple product for general diesel fuel-system maintenance.
I also like the flexible dosing. I can work out the amount based on the fuel in the tank instead of always using a complete bottle.
STP Diesel Injector Cleaner
STP Diesel Injector Cleaner has a more specific focus.
It is made to clean diesel injector deposits and is marketed to help restore engine performance, smooth rough idling and support fuel economy.
STP says its product is suitable for diesel engines including DI, IDI and common-rail systems. It recommends adding the entire 200ml bottle to a 50–60 litre tank every 3,000 miles.
What is STP diesel injector cleaner used for?
STP is mainly aimed at deposits in diesel fuel injectors.
If deposits affect the injector spray, the engine may not run as smoothly or efficiently as it should.
That makes STP a product I would consider when injector cleanliness is my main concern.
Why would I choose STP?
I would choose STP if I specifically wanted a diesel injector cleaner.
The treatment is also simple. You add the full bottle to a 50–60 litre tank and follow the recommended interval.
Redex vs STP: What’s the Difference?
The main difference is product focus.
Redex Diesel System Cleaner has a broader fuel-system purpose and also targets injector deposits.
STP Diesel Injector Cleaner puts more emphasis on cleaning the injectors.
That does not mean STP is proven to clean injectors better than Redex. I would not make that claim without a proper independent test comparing both products under the same conditions.
For me, the simple comparison is:
- Redex: broader fuel-system maintenance
- STP: more direct injector-cleaning focus
- Redex: flexible dosing
- STP: simple fixed treatment
- Redex: good for routine fuel-system care
- STP: good when injector cleaning is the main goal
Redex vs STP for Dirty Diesel Injectors
If I suspected that my diesel injectors were dirty, I would consider both products.
Dirty injectors can affect fuel delivery and combustion. Depending on the cause, a driver may notice rough idle, hesitation, poor acceleration, smoke or changes in fuel economy.
STP is the more direct choice because its Diesel Injector Cleaner is specifically made for injector deposits.
Redex is also relevant because its Diesel System Cleaner targets deposits in the fuel system and injectors.
So my choice would be simple:
For injector-focused cleaning, I would pick STP.
For wider fuel-system maintenance, I would pick Redex.
I would still check the actual cause of the symptoms first. A faulty injector, fuel filter problem or another engine fault can create similar signs.
Redex vs STP for Common-Rail Diesel Engines
Many modern diesel cars use common-rail fuel injection.
These systems use high fuel pressure and precise injector control, so injector condition matters.
STP specifically states that its Diesel Injector Cleaner is suitable for common-rail diesel engines.
Redex also markets its Diesel System Cleaner for diesel vehicles, including diesel cars with modern fuel systems.
I would still check the product label and vehicle requirements before use.
If a common-rail injector has an electrical or mechanical fault, an injector cleaner will not repair it.
Redex vs STP for High-Mileage Diesel Cars
An older diesel may have more deposits in its fuel system simply because it has covered more miles.
That does not mean the injectors are damaged or automatically need cleaning.
STP also offers a High Mileage Diesel Injector Cleaner for vehicles with more than 75,000 miles or 120,000km.
If I owned a high-mileage diesel, I would check the symptoms and service history before choosing a cleaner.
Mileage alone would not be enough for me to decide.
Redex vs STP: Dosage and How Often to Use Them
The dosing methods are different.
Redex dosage
Redex recommends 2.5ml per litre of diesel.
For a 50-litre tank:
50 litres × 2.5ml = 125ml
So 125ml is the dose for 50 litres of fuel.
I would always check the bottle instructions before using the product because dosing instructions can change.
STP dosage
STP recommends adding the entire 200ml bottle to a 50–60 litre tank.
The recommended treatment interval is every 3,000 miles or 4,800km.
Which dosing method do I prefer?
For simple use, I prefer the STP method.
You use the full bottle with the recommended amount of fuel.
For flexible dosing, Redex has the advantage because you can measure the amount based on the fuel in the tank.
Redex vs STP: Which Is Better Value?
I would not compare the products by bottle price alone.
I would compare the cost per treatment.
For example, Redex’s 250ml bottle can provide two 125ml treatments for a 50-litre tank. STP’s 200ml bottle provides one treatment for a 50–60 litre tank.
Before buying, I would check:
- Bottle price
- Bottle size
- Number of treatments
- Fuel volume treated
- Recommended treatment interval
- Cost per treatment
This gives a better value comparison than looking at the shelf price alone.
Can You Use Redex and STP Together?
I would not use Redex and STP together just to try to get a stronger cleaning effect.
Both products are made to deal with deposits in the diesel fuel system.
There is no good reason for me to assume that combining them will give twice the result.
I would choose one product, follow its instructions and see how the car responds.
Can Redex or STP Fix a Bad Diesel Injector?
No.
This is an important difference between cleaning deposits and repairing an injector.
A diesel injector cleaner may help when deposits are part of the problem. It cannot repair a physically damaged or electrically faulty injector.
A serious injector fault may involve:
- Damaged injector nozzle
- Internal injector wear
- Electrical failure
- Excessive fuel return
- Fuel-pressure problems
- Other fuel-system faults
If the car has severe symptoms, I would get it checked instead of repeatedly adding cleaner.
Redex vs STP: Which One Should You Buy?
I would base the choice on what I want the cleaner to do.
Choose Redex for general fuel-system maintenance
I would choose Redex if I wanted a simple diesel fuel-system cleaner for routine maintenance.
The flexible dosing also makes it useful when the fuel tank is not full.
Choose STP for injector-focused cleaning
I would choose STP if my main concern was dirty diesel injectors.
Its product focus is more specific, and the treatment method is simple.
Choose neither as a repair
If the engine has serious running problems, I would not expect either product to fix a damaged injector.
A cleaner makes more sense when deposits are the likely cause.
Final Take of Redex vs STP Diesel Injector Cleaner
I would give Redex the edge for general diesel fuel-system maintenance.
I would give STP the edge when the main goal is diesel injector cleaning.
I would not claim that one product definitely cleans better than the other without a fair independent test.
So my choice is:
Redex for wider fuel-system maintenance.
STP for a more direct injector-cleaning purpose.
If your diesel has serious running problems, I would diagnose the cause before relying on either product.
FAQs
Can I put diesel injector cleaner in a half-full tank?
Yes, but the amount depends on the product. I would follow the dosage on the bottle.
Should the engine be warm before adding injector cleaner?
Usually, the additive goes into the fuel tank before driving. I would follow the instructions for the product you use.
Can I use diesel injector cleaner in a van?
Yes, if the product is suitable for the van’s diesel engine. Check the label before use.
Can I use injector cleaner every time I fill up?
I would not do this unless the product specifically recommends it. Follow the stated treatment interval.
Does diesel injector cleaner replace an injector service?
No. A fuel additive does not replace injector testing, cleaning or repair when a fault exists.
Can I use injector cleaner with premium diesel?
Check the product instructions first. I would avoid mixing different fuel additives without a clear reason.
Is injector cleaner useful for short-trip diesel driving?
It may help with fuel-system deposits, but it cannot solve every issue linked to frequent short trips.
Can I use petrol injector cleaner in a diesel?
No. I would use a cleaner made specifically for diesel fuel systems.
How often should I clean diesel injectors?
There is no single interval for every vehicle. I would follow the cleaner’s instructions and the vehicle’s service schedule.
