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Ask Honest John: What is Redex and when should I use it?

Honest John answers reader queries about whether to use Redex or not
Redex injector cleaner - Halmer
I put the desired amount of this into my 20,000 mile, two year old 2.0 litre Passat on Friday morning.

The old adage don't fix if it aint broke comes to mind as it's started awfully on Saturday and Sunday morning from cold. Never had a problem with it before and it's never missed a beat. I jus hope that I haven't ruined something and it was dodgy petrol or something.

It seemed to be fine this morning however.

Tags: technical issues petrol or diesel? repairs consumer rights maintenance and servicing

Redex injector cleaner - Dynamic Dave
The redex *might* have shifted some carp from somewhere & temp partially blocked something else. It *could* have then got to work again and finished cleaning the remainder of the carp out.

Redex injector cleaner - pienmash
my dad always told me to boot(go quite fast) the engine after using redex to get all the old crap out,are carp a comman redex problem then dave ^^^^^sorry couldnt resist
Redex injector cleaner - Aprilia
Why did you put Redex in?

With any car, keep clear of additives of any sort. Just replace the recommended fluids at the right intervals. If you want to spend money on the car then treat it to an extra oil change.
Redex won't do anything on a modern car other than create extra smoke and muck (deposits) in the cylinders - a 20k mile Passat should have a spotless fuel system (unless you have been filling it up in Greece!).
Redex injector cleaner - Halmer
I put Redex in because HJ recommends that you use it periodically.
Redex injector cleaner - Halmer
Your theory sounds a bit fishy to me DD
Redex injector cleaner - Dizzy {P}
Halmer, I suggest that you put your trust in Aprilia. If you click on his profile (i.e. click on the name at the top of his posting) you will see that he has a great deal of technical knowledge and experience.
Redex injector cleaner - Halmer
I thought that I could recall HJ writing that you should use it once a year particularly if you use supermarket petrol.

As my car is in its third year I thought that it may help and at worst be a waste of £4.

Maybe it will clear when I refill next time.
Redex injector cleaner - dieselhead

I would have thought that the occasional use of additives when using supermarket petrol would be a good idea. My understanding is that the quality of uk petrol is "monitored" - this is a bit different from regular inspections with fines etc. for petrol not meeting the specification.
In any case the quality control of the base fuel or additives used by supermarkets is likely to be inferior to that of the big oil companys.
Redex injector cleaner - Aprilia
In any case the quality control of the base fuel
or additives used by supermarkets is likely to be inferior to
that of the big oil companys.


Oh no, not again....

I am not aware of any motor manufacturer who recommends the use of fuel additives - in fact I think you will find most handbooks specifically warn *against* using them.
I also think you'll find that Redex caution you that using their additive may invalidate your warranty and suggest you check with your vehicle manufacturer prior to use.

There are numerous fuel additives on the market (STP, Wynns, Holts, Forte etc etc) and I am not aware of a single independent test which validates the claims made for these additives.

Redex creates a lot of particulates (i.e. smoke) which I don't think would be healthy for the cat.
Redex injector cleaner - dieselhead
In any case the quality control of the base fuel
or additives used by supermarkets is likely to be inferior to
that of the big oil companys.

Those are not my words - I'm repeating what i was told at a meeting by an engineering prof. that's a part time advisor to the oil industry.

Redex does produce alot of particulate matter used in high concentrations - I would not pour the stuff into throttle bodies or cylinders on a catalyst equipped car.
Could cause overheating of the catalyst if you were very unlucky.

An additive added at a low concentration to the fuel should help keep injectors clean and shouldn't do any harm and may do some good especially if fuel quality is questionable.

The issue with the motor manufacturers is that additives designed to increase octane ratings containing heavy metals such as phosphorus or manganese can degrade catalysts.

As far as i know, the injector cleaner additives don't contain anything harmful to emission control systems.
Redex injector cleaner - CG
I have used Millers Diesel Plus for most of the 87K in my 406 HDi - originally recommended by none other than HJ. It does improve consumption and slightly reduces the typical diesel noise. It is supposed to help lubricate the high pressure pump, now that low/ultra low sulphur fuel is with us. It also allows soot etc to be blown out of the exhaust when accelerating hard, instead of retaining it in the system. I reckon it's worth using - the consumption gain pays for it anyway.

Redex injector cleaner - Aprilia
In any case the quality control of the base fuel
>> or additives used by supermarkets is likely to be inferior
>> that of the big oil companys.
Those are not my words - I'm repeating what i
was told at a meeting by an engineering prof. that's
a part time advisor to the oil industry.

At risk of repeating an old discussion - Tesco sell 1/8th of all petrol sold in the UK. They don't have their own refinery; in fact I gather that Tesco have an agreement with Esso for fuel supplies.
As far as i know, the injector cleaner additives don't contain
anything harmful to emission control systems.

OK, what's in it then?
Redex injector cleaner - Kevin
Aprilia said:

>OK, what's in it then?

Snake oil?

Redex injector cleaner - Ben {P}
I thought that manufacturers stated do not use any additives for legal reasons. The point being that the vast majority of products are snake oil and can cause harm.

However, there are some products on the market people beleive do have beneficial effects, and according to a number of private oil analysis results do not cause any harm.

I have heard that BMW even have tested Red Line SI-2 and given their approval. Here is a bit copied directly from the product description on their web-site:
"SI-1's injector and valve detergent is a concentrated package of the most powerful high-temperature detergents available to clean gasoline fuel injectors, intake valves and combustion chambers. SI-1 Complete Fuel System Cleaner can clean injectors to nearly 100% efficiency in one treatment. The cleansing effect on injector deposits can raise fuel economy approximately 12% or even greater, depending on the condition of the injectors. Although many gasolines advertise injector cleanliness, GM presented a paper to the SAE which indicates that their customers encountered injector plugging with all major brands of gasoline (SAE 861533). SI-1 also contains detergents and a synthetic upper cylinder lubricant which will help clean the intake valves, pollution control valves, combustion chamber deposits and carburetors. One bottle of SI-1 to a tank of fuel can reduce octane requirements by two numbers. SI-1 also protects the fuel system from rust. One bottle treats up to 100 gallons. Safe for continual use. "

They claim GM believe injector plugging has occured with major brand fuels in the US- is their fuel of inferior quality to UK fuel?

They claim this product is quite different to the kerosene based cleaners (ie redex etc).
Redex injector cleaner - Sooty Tailpipes
RedEx do two products for gasoline engines, One is an olefin solvent upper cylinder lubricant, the other an injector cleaner mainly isopropanol and oxygenates.
The poster is talking about the latter, which is simply.to clean deposits left by fuel which has evapourated (gums varnish)

the former is the one which causes the smoke and is mainly just a visual effect and for older carburettored cars
Redex injector cleaner - Glaikit Wee Scunner {P}
Just about finished a bottle of Miller's Diesel Powerplus Cleaner.
No improvement at all noted in performance or economy.
I usually use Total diesel as that is the locally available brand.
I wasna fu but just had plenty.
Redex injector cleaner - Roger Jones
Search the Forum for "G 001 700 03" and you will find lots of boring comments from me about how VAG's own injector-cleaner fuel additive worked a treat in curing my Audi 100's cool-running problems (clogged up by short trips) and is something I continue to use in all three of my ageing vehicles, which all run as smooth as silk. HJ originally recommended it to me and my mechanic shares his and my faith in it.
Redex injector cleaner - Dude - {P}
My recent experience of using Millers Diesel Power Plus does not follow those of Glaikit Wee Scunner, in that I have gained an extra 3.5 mpg and the engine is running much smoother.
So contrary to earlier comments, there are situations where these products do give quantifiable benefits.
Redex injector cleaner - MarkSmith
I have no opinion on whether or not these things work. I've heard compelling arguments both ways.

However something I think is being overlooked by people saying "It didn't help me" is that even if these things do work, they will only give an improvement if your car is suffering from the thing they aim to improve. My car may be running lumpy and no additive in the world will help because it's down to a faulty distributor cap!

If you don't have a blockage / gum etc., there's nothing to unblock/ungum. That doesn't mean they wouldn't ungum something if there was gum. (Neither does it mean they would.) They'll only improve your MPG if something they (aim to) affect is causing poor economy.

Sounds pretty obvious I know, but I think it it overlooked.

Redex injector cleaner - Aprilia
Modest build up of gum on injectors is not an issue on modern vehicles simple because the engine control system uses feedback control. If the injector delivery volume per unit time falls slightly then the ECU simply opens it for a little longer to compensate.

The advertisers of these additives are eager to show gum on the back of inlet valves (left there by the evaporation of the petrol) but in practice this is modest and may even be beneficial (by creating microturbulence in the inlet air stream).
Redex injector cleaner - Ben {P}
But in the photos and on heads i have removed, build up on the back of valves could easily be 0.25 to 0.5mm, which is as much as the difference a high-lift performance cam could make to valve lift. And given the performance benfits i have witnessed produced by such cams, i would have to conclude that a build up would have a noticeable effect upon performance. I wonder why engine builders/tuners would take a lot of care creating a specific finish and reshaping valves if it did not make a difference. I thought "swirl effects" on the inlet side were created by skillful manifold design etc. Ideally atmoisation of fuel should be perfectly uniform, i cannot see how this would be created with random bits of dirt on the back on an inlet valve.

Having said that most of the crap on my 16v VW head @100k miles was on the bottom of the valve ie the flat part. There was very little on the stem and back of the valve. Car was run on Shell Super/Optimax and the VW injector cleaner. It looked better than many of these heads i have seen, but due to the variables involved i could not conclude whether it was due to fuel or not.

The oil nutters in the states have not noticed any detrimental effects in their oil analysis when using the *right* products, but would cylinder deposits show up in oil analysis?
Redex injector cleaner - Nortones2
Would not emissions control be compromised in such circumstances? And another effect would be that the injector spray pattern would eventually be affected as the fouling process continued? Dribble factor is not just cosmetic in this case!
Redex injector cleaner - dieselhead
Agree with Nortones, even if the emission control system compensated for the reduced fuel deliver caused by deposits, economy, emissions and driveability would all suffer.
The injector spray pattern would be affected i.e. not atomise the fuel as finely or spray too much fuel into the wrong place causing fuel "puddling" or lube oil contamination.
Redex injector cleaner - baldingbuthandsome
To all that have posted here, I run a small haulage company and therefore monitor costs of fuels and oils very closely as our line of business has rather narrow margins in some cases.

It's interesting so many of you dissmiss the benefits of additives. I've recently changed the oils in our Merc Actros and the rear axle oil as a base is the exact same oil as the gearbox. However the additive package which has been developed for the rear axle more than doubles the price of the gearbox oil.

To quote you the gearbox oil is a Full synthetic EP 75/85 priced at £106.18+Vat for 25 Litres. The Rear axle oil is a Full synthetic syntogear FS.TDL 75w/85 priced at £214.93+Vat again for 25Litres. And believe me I shopped around!! The engine oil is also heavily fortified with additives and has alot of calcium in it to neutralise the acid formed by the carbon deposits suspended in the oil. These acidic carbon deposits are what normally degrade the oil by eating away at it's lubricating properties. Abit like soap works. (Yes I know soap is generally alkaline but it has the same effect on the oil molecules). The additive package goes way beyond just calcium but together they extend the oil drain interval from 35000km to 120000km. Although I personally think this is abit too far! But thats what Merc have programmed the dash to!

The difference is the additives in the Rear axle oil guard against the shearing effects of the diff from burning the oil. The base is the same.

I'm currently trialing the Redex diesel injector cleaner which claims to improve fuel economy. The truck has averaged 7.9/8.0mpg over the last 6 months. The Redex has now been in for a couple of weeks and the first weeks average was 9.0mpg. I was very surprised at such a difference but the truck had been on lighter trailers that week which therefore answered the large jump. However the monday of the 2nd week the truck was on heavy work and averaged 9.9mpg. This a record by an awfull long way! A 44T artic doing 9.9 to the gallon is extremely good!

I'll post again at the end of the week when i know what it's done. I don't just go by the reading on the dash either for those of you who are going to say it's fooling the system!
Redex injector cleaner - Armitage Shanks {p}
Referring to earlier posts, surely the difference between say, BP standard diesel and BP Ultimate is additives? If there is no difference what justifies the 4-5p price difference?
Redex injector cleaner - baldingbuthandsome
The BP Ultimate and Shell V-Power ranges of diesel is quite in depth and I don't yet understand how it's done. Simply put they reconstitute and change the chemical formula make-up of natural gas so that it stays in a form similar to diesel (i think the petrol version is made in the same way). Hence if you fill your car up with one of these 2 you'll notice there is no smell. The reason being natural gas has no smell. What we smell as gas is Butanethiol added to the gas so we can detect a leak. Obviously yes there are a lot of additives such as detergents etc also added but this is the main difference. They make it like this as it burns much cleaner. If I could buy it in bulk I'd run my trucks on it!
Redex injector cleaner - Number_Cruncher
>>It's interesting so many of you dissmiss the benefits of additives.

There's an important difference though.

If additives have been added to the engine/gearbox/axle oil or to the road fuel to meet the Mercedes specification and the relevant British Standard respectively, then, that is a different case to pouring some spurious jollop into the tank.

If the oils for your Actros meet the requirements of the relevant MB spec sheet, then, they have been tested in accordance with MB's requirements, and are therefore recommended for use.

Alas, you're mpg results are just one point, one result, and could easily be the result of a different driving style, different routes, different loadings, different temperatures, and different combinations of these and other factors. If results from 100 trucks were presented, then, it could be more meaningful.

I forgot to say, back in the 70s and 80s, the Merc trucks my father ran used to use EP90 in the gearbox, and EP140 in the diffs.

Edited by Number_Cruncher on 18/03/2009 at 11:35


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