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Discussion Starter #1
Running the risk of this being discussed to death here, but can't find any previous posts.

With the impending MOT changes, my emissions are concerning me. Only had my bus for 3 months but it is smoky, as I'm sure most are. It's a 2.5tdi 03 plate.

If anyone uses an additive, what would you recommend. A friend of mine has told me BG44K or Millers and would like to hear if anyone has used these on here.

I've just filled up with V-Power fuel too, hoping to give the fuel lines a clean out with that too.
 

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Hello Sandym,

I've done my fare share of research into this sort of stuff (even before owning a T4). I've read quite a lot about additives, redneck tricks, fuel efficiency, engine treatment etc. on various forums (e.g. VWAudi, T4, pistonhead, brickwerks, Landyzone, some over in the US) in the last few years.

First and the golden rule is: service the vehicle according to the interval specified by the manufacturer using appropriate products. This is the best thing that can be done on a vehicle.

Next: the additives...short answer is there's no silver bullet out there. If there is, everyone would be using it. But if you must, then there are plenty of products out there claiming all sorts of miracles. There's no hard evidence of what's best product / practice, as far as I understand. Fuel industry is very secretive (as you might have guessed). All are based on comments / opinions / biased research articles online so I'd take it with a pinch of salt and see what convinces you and suits your needs.

WARNING: Experiment at your own risk...

In terms of the product that you can by, Millers Diesel Power Ecomax and Diesel Rhino seem to be the popular ones. Some say all these "fuel additives" and "engine treatment" products are snake oil. Some swears by certain products. No one is right or wrong. I've never used them. But I may try Diesel Rhino in near future.

Not quite an "additive" but LiquiMolly Diesel Purge is something to check out. Lots of YouTuve clips on this and it looks very promising. It can be poured into the fuel tank like any other additive, or you can play with the fuel lines and run the engine with it for deep clean, or next time you service fuel filter, fill the filter with it and pour the rest in the tank. I'm going to try this on my next oil and filter change.

In terms of the fuel, V-Power, followed by BP Ultimate, give you a good MPG and "treatment" of fuel and engine components. Supermarket fuels are frowned upon (due to the content of sulphur, which acts as a "lubricant", being very low) amongst diesel enthusiasts, unless you add some sort of additives. In my old A4 (1.9TDi AFN), V-Power gave me 3-4MPG more than the supermarket fuel (based on 2 tank full mileage, I think), where as BP Ultimate gave me about 2MPG more than supermarket fuel (based on 4-5 tank full mileage, I think).

Some rednecks and cheapskates (including me) find that above methods are can become expensive (about £10-15 more per fill up, though the MPG result and "perceived" performance are observable). Some make home-blend fuel additives! Common home-blend chemicals are two-stroke oil (low ash, mineral, and NOT red in colour) for lubrication and cétane booster (2-EHN) for higher combustion rate. But the ratios of these chemicals per 10L of diesel seem to be quite variable (and no hard evidence). Usually forum comments mention ratios around:

1:200-250 for two-stroke oil (i.e. 40-50ml per 10L diesel) and
1:1000 for 2-EHN (i.e. 10ml per 10L diesel)

You can get 2SO and 2-EHN cheaply online. BUT, depending on your engine, these can be beneficial or actually detrimental. For example, old diesels like Defenders and Mercs benefit from added lubrication, but any "newer" engines (PD, more electrically controlled engines) are so refined it'll actually cause damage to fuel pump, lines, injectors and other vital components (based on others comments on forums). I made home blend of 300ml 2SO + 50ml 2-EHN on the same A4 with supermarket fuel: improved about 3-4MPG, I think, and did it for nearly 1 yr (10,000miles) (I don't remember exactly but it was as good as having V-power without the premium price).

That's pretty much it in terms of "adding" something into the fuel tank.

BUT, also consider... Many different things cause smoky engine. If you're experiencing smoky engine, then I'd investigate relevant components themselves. This means VAG-COM diagnostics for fuel / air ratio, fuel pump timing, glow plugs, MAF sensor, possibly cleaning out components like intake / exhaust manifolds, turbo, EGR, injectors, etc. T4s have plenty of mechanically driven components which can be replaced / serviced. For example, our T4 was smoking white puffs in cold; replaced glow plugs, had pump timing adjusted and no more smoke.

Once again, this is just purely based on what I've read online (don't believe everything you read on the internet), and some first-hand experiments. Fellow forum users may agree or disagree on what I found out. Every vehicle, every engine is serviced differently, treated differently, and responds differently to anything done to it. So there's no clear answer.

Sorry, lots of worms came out of the "additives" can!

I hope this helps in getting you started on how to sort out your smoky engine before the MOT.

Happy motoring!
 

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Use the best fuel, V power or BP Ultimate.. Additives. I used Diesel Rhino, when I first got the van.. (2.5TDI ACV). It is supposed to be the best.. The only thing that put me off Diesel Rhino was that if I got it on my hands, I seemed to be able to taste it in my mouth..I suppose, just wear plastic gloves and you won't get the problem..

But once it has cleaned the engine out a bit, just use the best fuel to keep it good...
 

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Discussion Starter #5
Cheers Defever......thats given me plenty food for thought.

I was also looking into replacing/servicing parts that I can. Although I've not been able to pin down the smoke to a particular colour. It doesn't seem to be too white, blue or black so I can't seem to decide which part to look at deeper first.

Thanks for all the advice though
 

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i used bg44 for higher mileage vehicle, however for under 100k i would go with terra clean.
terra clean was backed up by edd china (wheelers dealers) however it could be so effective that itll uncover underlying issues. for example you could find out that you've got leaky injector, or injector seals has perished, or some other leak ,as the sot that was sealing it previously would/should be gone.

saying that, as per advice above, run full diagnostic as the smoky diesel could be many different things and many could be relatively cheap to fix. once sorted, treat your engine best you could afford T:
 
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