Are diesel additives worth it?

[Barchettaman]

Wouldn’t the petrol ‘float’ on top of the diesel anyway, or am I making that up?

[Kernowlokal]

I use the Millers Ecomax in a Volvo D5. Gained about 2mpg from it, plus it pulls better and runs smoother. If someone borrowed my car and put some diesel in without the additive, I could tell straight away as it ran so much better with it. I sell it, so speak to others about what results they get, most like it, but some people find it does nothing for their engine. Like most things, some people see a benefit, others don't. It's cheap enough to give it a go and see what you reckon.

[Second Best]

I just use Shell Vpower diesel in my R320. Nothing else. Driving it back from Lincoln a few days ago I got 36.4mpg and that was at 0.83 leptons with the air con and heated seat in action.

[AlexS_LDN]

LarsG said:

Suggest you have your car checked,

"Diesels actually do not suffer exactly the same "knock" as gasoline engines since the cause is known to be only the very fast rate of pressure rise, not unstable combustion. Diesel fuels are actually very prone to knock in gasoline engines but in the diesel engine there is no time for knock to occur because the fuel is only oxidized during the expansion cycle."

"Generally, diesel engines operate well with a CN from 48 to 50. Fuels with lower cetane number have longer ignition delays, requiring more time for the fuel combustion process to be completed. Hence, higher speed diesel engines operate more effectively with higher cetane number fuels."

In the EU Cetane level is set at 51.

"Diesel engine knocks when there is accumulation of fuel in the combustion chamber which happens when the injected fuel fails to burn as there will a huge delay period. And at a specific time all mixture burns simultaneously which causes increase in peak pressure and shock waves travel at higher speeds and can lead to permanent damage to piston crown and cylinder wall and head."

Therefore unless BMW say it can only run on CN 60 you might want to have the car checked out. There might be a software or sensor issue.

Edited by LarsG on Sunday 6th January 21:06

The notorious "swirl flap" problem never went away from BMW engines, although it was the earlier N47 4 pots that sufferered these flaps getting ingested by the engine and wrecking pistons after they work loose (there were an emissions reduction system), the M57 six pot was overlooked. Couple with timing chain issues (4 cylinder N47 diesels needed engine removal as the chain and guides are awkwardly at the very back) it could be something else. If the B57 engine is a slight evolution of previous engines (swirl flaps used in conjunction with DPF to reduce emissions) I would be wary of any knocking sounds. My brother's engine seized and it had to be replaced. You either get a good BMW diesel, or in rare cases a very bad one. Or the previous owner could have thrashed the life out of it first...

Before going Japanese (at present) I have had only BMWs either with 4 pot diesels, but mainly 6 (325d, 530d, 535d)... the majority were fine, only two of the cars suffered with the timing chain and swirl flap issue. I never had any engine knock though now and then I would even use supermarket fuel, but no issues. I personally found the additives did nothing, and most manufacturers warn against adding such in the tank. I use the V Power or Ultimate most of the time

[TurboRob]

Hydra's "Diesel Power Blast" injector cleaner made a noticeable difference to a 145k mile Focus TDCi sh!tbox/winter hack I'm running at mo.

https://www.hydra-fueladditives.com/diesel-power-b...

Smells very similar to Millers - not sure if these products use aromatics or it means similar main ingredients.

[Alex_225]

A friend of mine has an old C220 diesel and it was running a bit rough etc. I helped her out with a couple of bits and said it can't hurt to use one of these additives.

As a thank you she bought me a bottle of Redex as she got one for her car as well.

I put a shot in my E320 CDI as thought it can't hurt, I use V-Power diesel anyway and I haven't noticed any difference. My other half has a CLS350 CDI but uses normal Shell diesel so put a shot in that. Did 500 miles or so in it over Xmas and the returned MPG was 43-44mpg. May be complete placebo and me subconsciously driving more gently but usually the car shows about 39/40mpg on a run.

Either way for the sake of £5 for a bottle that gives enough for four tank fulls, if you're prepared to do it by the book it's worth trying. Near empty tank, shot of additive and fill again. You may notice a difference.

[Sa Calobra]

Glasgowrob said:

always whacked a little bit of 2 stroke oil into the taxis

and we've run up some stellar mileages 400-500k without any problems never changed anything injectors or turbos on anything we've run the last 10 years

Really, this is on modern diesels??

[TheDrownedApe]

On hundreds of forums this topic always divides opinion. There is no definitive answerwhjch you can hang your hat on. A few still reference the Tiff video but alas that's old and been pulled apart.

If you want to use it then do so, if you see a benefit then GG.

[Evercross]

After reading another thread on the same topic I started adding pure 2-Ethylhexyl Nitrate (the active ingredient in super-diesels as used at the refinery) to a tankful. Being doing it for about 6 months now and (pre-lockdown) I have recorded a measurable improvement (based on brim-to-brim fillups and odometer reading, not fuel computer) in MPG of about 5 miles over previous.

You can get it in litre bottles for about £11 delivered. Adding it at the recommended rate of 10ml/10litres it goes a long way.

There's plenty scientific study to say 2-Ethylhexyl Nitrate actually works as a fuel improver and AFAIK the branded diesel additives are just expensively repackaged versions of it. One major downside to it is that it stinks so don't spill it on your hands or in your boot.

People going on about adding 2-stroke oil - that's essentially just more (poorer) fuel.

Edited by Evercross on Tuesday 26th May 22:12

[Chlorothalonil]

Have tried various products including Archoil and Forte, with no discernible improvements.

[A1VDY]

Adding 2t oil isn't about increased mpg its about getting mechanical components to last longer. Better to use it in older Diesels with a mechanical pump and injectors. It lubricates the upper cylinders too. Can't be used in new stuff with a dpf though..

[NGRhodes]

A1VDY said:

Adding 2t oil isn't about increased mpg its about getting mechanical components to last longer. Better to use it in older Diesels with a mechanical pump and injectors. It lubricates the upper cylinders too. Can't be used in new stuff with a dpf though..

http://www.fuelexpert.co.za/2-stroke-oil-in-diesel-technical-study.php - shows 2 stroke oil make minimal difference to the lubricity of diesel.

[MethylatedSpirit]

I used to pour 20 litres of veg oil in my polos tank


Not sure if counts as an additive.

[S8QUATTRO]

Any thoughts on the Lucas Injector Cleaner - also referred to as Upper Cylinder cleaner, it seems thicker than the redex type additives but still goes into the fuel tank.

[Rich Boy Spanner]

Additives depend on your driving cycle. If mostly motorway or A road and decent miles you don't need them. Maybe use a some V Power diesel once in a while and an additive once or twice a year at most. If a lot of urban then you absolutely do need them or use the V Power diesel type of fuels regularly.
I ran diesels for 20 years on motorway using Tesco diesel and an additive once a year and had no bother at all. We also have an old Toyota with the 2.2 d4d engine which does more short journeys and it smokes like hell and clogs up the EGR valve unless it has V Power or Tesco plus Redex. You really notice the difference in a diesel without a DPF.

[Hugo Stiglitz]

I chuck in Shell VPower every 2-3rd tank and just drive.

[Scarletpimpofnel]

Pica-Pica said:

I am in the process of assessing different fuels for my 66 plate 335d. I usually run Shell V power diesel, the reason being in hope it will protect the dpf. However, I noticed a slight diesel knock on light throttles that was not there before; I was not sure if I was running Shell V power or had a tankful of Shell fuel save at that time. So I researched on line, and a few people were recommending BP Ultimate. Pricey, but the knock (which I must say very, very slight) went. I had two tanks of BP Ultimate, then topped up with Shell V power. Still OK, then on a nearly empty tank I topped up with Shell Fuel Save (standard Shell diesel) - result, knock returned after 20 miles or so. Again, I am in the process of next trying BP Ultimate, despite the cost, for two or three tankful, then Shell V power again to compare to BP Ultimate, and then back to Shell Fuel Save on it’s own, and then with additives. Apart from costs, the mpg has been similar, and any performance difference is impossible to gauge on the 335d. My main issue is to get back to no-knock on light throttle increases (such as when using cruise control). It will probably be a few months before I conclude anything.

That was all about fuels being able to minimise a particular knock. Additives may be tried in due course. Keen to hear other comments.

I'm interested in what you say about "knock". I generally use BP fuel and mostly use BP Ultimate diesel. I did find when using "standard" diesel my car developed some "hesitancy/knock" at low speed/low throttle. It was quite disconcerting and felt very rough just as knock would. Now I use BP Ultimate more regularly the hesitancy has disappeared.

I cannot say the hesitancy was fixed due to the use of BP Ultimate as it might be that I simply had a poor quality tank of fuel at some point or a service change of fuel filter etc actually fixed it.

[Lester H]

I very much doubt it, but having had several diesels in the family, I suspect that the occasional use of a premium brand of “ super” fuel is worthwhile before a good long run or an MOT.