It needs an oil change, especially that engine which should have an oil and filter change at least once every year unless you travel more than 10k miles a year, some would advocate even more frequent servicing on this engine (i would too) some would not.

A full can of Forte, good stuff that, through the tank stands a good chance of getting it through the test, it used to be advised to go half and half, ie half the can straight into the fuel filter (can't recall if the one on the HDi can be manually prefilled before offering up) the other half into the tank, but if you don't want to take the fuel filter off shove the canful directly into hopefully not a full tank of fuel for a strong mix, then give the car a serious thrashing for a few dozen miles to blow the stuff through the injectors...if you have to put some fuel in anyway, splash out on the premium stuff for a while.

Some of us believe fuel treatments work, i along with many others use Millers fuel treatments on every tankful, others think differently, again you must decide who you believe.

Don't forget to ave a poke nose at the air filter, if that's been in two years its probably well dirty now and that won't be helping airflow.

One other thing, is it putting out black smoke under acceleration, could it have been remapped a little too enthusiastically? even if it has the Forte fix has as good a chance as any.

These engines (I have had one for 10 years) benefit from fresh oil and filter about every 8000 miles. The handbook probably says 12,000. If you get this done (properly, not just a quick suck-out) and follow it with 20 litres of Shell V-nitro fuel, your problem should go away. Just for luck add some injector cleaner to the tank.

My last reading was 0.32.

Edited by Andrew-T on 14/11/2019 at 21:55

An oil change is only likely to resolve an engine smoking condition if the oil has sheared and/or been diluted with fuel so that its viscosity is lowered enough to significantly increase the rate that it is getting past the piston rings and being burnt.

This is more likely to happen with "modern" low viscosity oils.

I can not think of ANY way a new oil filter will have an immediate effect on engine smoke.

I had a Renault 5 Campus fail on "visible smoke" (Long time ago, I don't THINK they had instrumentation to measure it then, so I think it was subjectively assessed by the tester)

I changed the oil (Castrol GTX 20W50) and added Wynn's viscosity improver (Stuff looks like honey. Don;t use honey) . This was probably overkill, since I also cleaned out the crankcase breather system, AND I changed the MOT tester.

It passed,

I can't say for sure what fixed it, but my guess would be the new MOT tester, with cleaning the crankcase breather as second choice.

BUT the principle remains. If you hope to stop it smoking with an oil change:

(a) Good luck with that

(b) Use THICKER OIL

However, a modern diesel will call for a low SAPS oil to protect the DPF,

I dunno offhand if these are available in the higher viscosity ranges, but IF you can't get one, you could put high SAPS in for the MOT test and then swap it out after.

If doing that I wouldn't change the filter for the test, to reduce carry over into the replacement low SAPS oil.

Edited by edlithgow on 16/11/2019 at 01:35