Can MOT smoke test cause problems?
 

My venerable (225,000 miles and still going fine) CDT Tourer had its MOT test recently, and passed the smoke test just fine. Driving the car a few days ago, I noticed that it was putting out a fair bit of smoke on acceleration, which is something I hadn't seen before, and I was wondering whether this could be the result of some damage done by an over-exuberant smoke test.

I hope not, of course. It is entirely possible that is has been happening for a while and I just hadn't noticed before, but I don't think so. Anything else I should be looking at for an explanation? It's certainly not down to the mileage per se, as I only do at most 3-4,000 or so miles per year, and it's definitely a recent phenomenon (i.e., it wasn't there when I had 220,000 miles on the clock).

No this isn't damage from the smoke test. These diesel engines are limited, and they should rev freely to that limit with no problems.

A bottle of decent injector cleaner, and if that doesn't help a full service - including cleaning the inlet manifold and MAP sensor, EGR and PCV should sort it.



















.

OK, I'll order a bottle of that magic injector cleaner whose name I have forgotten (LATER: Forte, ordered), and book it in for a full service. Relieved that it won't be damage from the smoke test - thanks!

An Emissions Test would only Reveal Failing Parts - NOT cause Parts to Fail ;)


My MOT Test Station has a Disclaimer - they won't do an Emissions Test on a Diesel unless there are Service Records to show the Timing Chain/Belt(s) have been replaced within a specific time frame.


what colour "Smoke" are you seeing ?





Paul.

Not really sure yet, only seen it in the dark.

You will find that the "Smoke" is more noticeable in the dark when there is someone behind you with their headlights on.;)

Hi John.
I think your full service will not include a manifold, EGR, or MAP sensor clean. That is something you need to do your self, or get someone to do it for you.

What colour is the smoke you are referring to, is it grey, blue, or black, ? if black check the intercooler pipes, and the O-rings, as well as your service of clean air filter, PCV, Fuel filter, also hopefully the MAF sensor is within spec & not starting to break down. ;)

I only drive around on light throttle and I reckon my engine rarely revs above 2500 - 3000 rpm and if I put my foot down I get smoke for a while as all the crud gets blown through. It will gradually clear but then I'm back to poodling about again.
I did have a problem scraping through the smoke test but last year I took it for a 5 mile run at 4000rpm and flew through. It's sound advice to get all the relevant items serviced but even when that is done you might, depending on your driving style you still may see a bit of smoke, and yes it does look worse at night.

It does strike me that the issue may simple be my latest tank of fuel. I filled up with Asda ultra low sulphur City Diesel this last time, without recalling that in the past I'd had noticeably poorer performance from this kind of fuel. I stuck a slog of Miller's in there, and I think there was less smoke afterwards, but it was still present.

i purchased some wynns emission reducer for the test and it flew through there is also some wynns called clean burn which is for smoke related issues rgds mark