MOT and diesel smoke test: Motoring Motoring Discussion forum

Motoring Discussion > MOT and diesel smoke test	Miscellaneous
Thread Author: Mr Moo	Replies: 9

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Thu 5 Dec 13 23:33

MOT and diesel smoke test - Mr Moo

I took our 61,000 mile '57 plate Land Rover Freelander 2 TD4 for its MOT today. Passed with no work or advisories, which is nice when your MOT falls at the same time as all the pre-Christmas costs!

On checking the MOT Test Certificate, it says:-

001 Smoke level is too low to be detected by analyser, vehicle has passed emission test.

I'm sure in previous years, I've had a print out of the smoke test. The reading has always been pretty low and well within the limit, but this is the first year that the smoke level has been too low to measure. Given that the car is six years old, it's blessed with no particulate filter. I always give it some welly on the way to the MOT to blast the carp out of the exhaust, but I'm a little surprised that the smoke level is too low to measure. I dropped the car off at 08:00 this morning and they didn't do the test until early PM, so the engine was probably relatively cold when they did the smoke test, which would normally make the smoke reading worse.

Given that all new diesels have DPFs now, what's the point of a smoke test on a post 2010 diesel? Surely wiping a finger in the exhaust and seeing whether it comes out clean is pretty conclusive evidence of whether the DPF is present and working correctly.

How come my pre-DPF diesel emits so little smoke that it doesn't register? If I boot the throttle when driving at night, there's certainly a haze illuminated by the following cars headlights.

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Fri 6 Dec 13 19:17

MOT and diesel smoke test - Shiny

>> Surely wiping a finger in the exhaust and seeing whether
>> it comes out clean is pretty conclusive evidence of whether the DPF is present and working correctly.
>>

If passing the smoke test just meant wiping a rag with some solvent on it in your tailpipe I think there would be a lot of cheating.

My VAG 3.0TDi has had it's DPF removed and never makes any visible smoke even at full bore there is no smoke showing against the headlights behind.

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Fri 6 Dec 13 19:37

MOT and diesel smoke test - NortonES2

If a Tyndall beam was used, none would pass!

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Fri 6 Dec 13 19:35

MOT and diesel smoke test - Old Navy

>> How come my pre-DPF diesel emits so little smoke that it doesn't register? If I
>> boot the throttle when driving at night, there's certainly a haze illuminated by the following
>> cars headlights.
>>

MOT = Engine not under load.
Giving it stick = Engine working hard.

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Fri 6 Dec 13 22:32

MOT and diesel smoke test - Fenlander

My Alfa was recorded as "No smoke detected" at its Dec 2012 MOT. The tester has written that on the sheet and signed it, the printout actually says test "Aborted". I was in the watching area and he did stick the probe up the tailpipe and rev it up a few times.

This Dec MOT the car was a little cool having stood 30mins. The first reading was 2.53 (3.0 allowable). The next 5 were an average of 1.09 so an easy pass. I'm happy with that at 160,000mls.

It did cross my mind there may have been a machine fault last year so he just signed it off by hand.

The only time I see visible light smoke in the mirror is if it's been pootled about for 20-30mls then you push it foot down to 4000rpm+. Then you don't see it again while driving briskly.

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Sun 8 Dec 13 09:16

MOT and diesel smoke test - Cliff Pope

Is it like the catalyst test on a petrol car? The car has to have a catalyst fitted, if original equipment, and the car has to pass the relevant emission levels.

But there doesn't actually appear to be a connecting link in the regulations, ie that the cat itself has to work. So if the cat is an empty shell, but the exhaust gas passes the test, then the letter of the law is satisfied.

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Sun 8 Dec 13 10:05

MOT and diesel smoke test - Robin O'Reliant

Mrs O'Reliant's diesel Saxo - which we owned from new - got a compliment from several MoT testers during it's life about it being unusual to see a car of that age with such low emissions. A 12 mile drive to the test centre with Millers diesel cleaning stuff in the tank and the revs up to the limiter may have made the difference?

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Sun 8 Dec 13 10:47

MOT and diesel smoke test - Dog

Reminds me of my mobile tuning days, XR3i owner had shaved his orf beard and , his missus told 'im to grow it back ASAP!

Anyway, the jamjar was running really bad and misfiring all o'er the place so, I bunged some STP fuel injector cleaner in the tank, ran it down the frog & toad and it worked a treat.

Had to spend another 45 mins on the car though, checking compressions/plugs/air filter etc. to warrant the 30 sovs.

:}

Last edited by: Dog on Sun 8 Dec 13 at 10:47

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Sun 8 Dec 13 11:43

MOT and diesel smoke test - Fenlander

Going back to 1990s cars I often wondered if they had off periods only resolved by bunging in a can of jollop.

If everything else obvious had been checked and the next options were expensive component swapping then a good way to get it out of the workshop for a while was to say the injector cleaner may or may not work but it was worth a try compared to the expense of other solutions. A parting shot of "give it a try for a few weeks and let me know" was appropriate and in 75% of cases folks were happy.

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Sun 8 Dec 13 14:08

MOT and diesel smoke test - Dog

Another 'trick' was to bung a tin of Wynns engine flush in (especially on the CVH) before changing the oil
(to GTX of course)

Worked wonders on hydraulic tappers.

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