Smoking diesels & MOT

[Arif110]

Often enough, I'll see a diesel vehicle putting out plumes of smoke/soot. I know that this for some cars may not be all of the time, and the engine might still be warming up, etc - but overall - how do smoky diesels manage to pass their MOTs?

Or is it that the MOT test doesn't care about smoke per se - rather various, specified gasses (e.g. NOX, etc)?


Arif

[Drive Blind]

they do get failed for excessive smoke,

an Italian tune up by myself used to get my dads smokey focus diesel through an MOT each year after the MOT guy failed it and started talking about replacing expensive injectors and the like.

Dad drove everywhere at <2000rpm.

[wiliferus]

Clogged EGR valves can give the impression of a poorly smokey diesel.

A bottle of Redex and a good Italian tune up will see most diesels right.

The main problem is that loads of diesels now aren't used for what diesels are intended. The chug around town <30mph slowly clogging themselves up.

I used to have a right snotty old Audi A4 1.9tdi. It had over 180k on the clock last time I MOTd it. The tester said it was one of the cleanest running diesels he'd seen for a while. I was using it for a 70 mile a day motorway commute which kept the internals nice and fresh

[Arif110]

Okay - phew! I've run my Toyota Landcruiser 120-Series from new to 130,000 miles so far - and 95% motorway, and mostly towards top rev's. I've changed the oil every 8K to 10K miles, and all other usual service items (it's a D4D). It's running fine so far thankfully - but I'm a 'worrier' and wonder if future smoking represents expensive issues.

I forgot about the EGR valve being one easily-rectified source of smoking issues - hopefully my hot-running history has helped keep that working better too. On my Landie (TD5), I disabled the damn thing, so easy - but apparently modern engines will really mind - and while we're there - does it matter that it throws a fault code/light - is that the only consequence?

[Bear Phils]

It takes a good amount of smoke to fail. Such as if your injectors had actually failed and you couldn't see out the rear window when you put the foot down.

[Arif110]

Bear Phils said:

It takes a good amount of smoke to fail. Such as if your injectors had actually failed and you couldn't see out the rear window when you put the foot down.

Well that explains it! On the one hand they use precision equipment to measure for specific baddie gasses - but then a 'Passed' car could still be making a moderate amount of visible smoke.

So hopefully I won't have to worry about the MOT and smoke for a while.

[lescombes]

Just put my Mazda Bongo through the MOT... it shares the WL-T engine from the Ford Ranger so not a super whizzy Common Rail HDi job....
MOT tester run the test 3 times...he thought his equipment was wrong ..even though I was 3rd test of the day)

The beast passed.... easily with the mean figure of 0.02 ...yep 0.02... Well I was using a mix of 25% Veg oil to Diesel...

I also keep the vehicle fully serviced too and Veg oil is known to clean out the engine and EGR.

The same applies to Delica's and the same/similar result can be obtained.... I still get a little puff of black smoke on hard acceleration but the veg oil keeps that under control and the engine clean....in bulk the veg is 92p litre or less... To be honest if you can get out of date or short date oil it doesn't matter.... it's not going on yer grub....