M.O.T. (am I wrong)

stewart_c · Post by **stewart_c** » 10 May 2005, 01:29

I have just had my MOT done today & the car failed on the emissions @ 3.6 & I was told that it required to be 3.0 or below.
I have no problem with the figures it is the remedy that has had me thinking.
To get it to pass the garage put some fuel treatment in & that was ok with me, but here is the query,they also changed the oil.The oil that was in had only done 800 miles& was fully synthetic so it was hardly over worked.
I think some one is haveing a laugh at my expence as the car (xantia td 196k )does not burn oil (except veggie[;)])& yesteday I gave it a good blowout just below the rev limit for a few miles.
Curious to know what others more knowlegeable than me think!
ps it passed after the treatments[^]

rossd · Post by **rossd** » 10 May 2005, 01:48

Old oil certainly wouldnt help the emissions test, especially on an old engine such as yours. They probably just changed it to be on the safe side, after all it did pass afterwards!!

citronut · Post by **citronut** » 10 May 2005, 01:48

first thing to check for diesel with high emissions is air filter,if MOT station where told before hand that your oil was fresh,you should not pay them for there oil or fitting time,when i take my customers diesel cars for MOT i get on main road put in 2nd gear throtle flat to floor for few seconds ,this usuly clears any smoke,regards malcolm

stewart_c · Post by **stewart_c** » 10 May 2005, 03:44

I suppose I should just be thankfull for a pass but if it does not burn oil (& it does'nt )then how can oil affect the emissions[?]

AndersDK · Post by **AndersDK** » 10 May 2005, 04:00

It's a wellknown "trick" to reduce emissions by replacing an oil near or overdue the service interval.
The reason is the engine oil gets contaminated with fuel, carbon, water and quite some other garbage from the combustion process over time.
Especially diesel engines holds a lot of carbon in the engine oil - hence the nasty "ink" when you replace engine oil on a diesel.
Also diesels are prone to build up carbon in general in the exhaust system by everyday mixed usage. This will show in a test.
As Malcolm writes it is rather easy to do a "first stage" cleaning.
Also referred to as "Italian tuneup".
We have had a few diesel owners here with mysterious "dead" diesel engines - caused by longterm usage in London-like traffic.
What happens is that the carbon build up in the exhaust becomes so severe that it restricts the exhaust - and hence the engine power.
Such an engine takes dramatic advantage from an Italian tune up - i.e. a long steady trip over an hour at least with engine at max revs in 3.rd or 4.th. You can litearally see the black carbon released from the exhaust the very first minutes - then calming down as the trip progresses. And the shift in engine power is amazing.

fastandfurryous · Post by **fastandfurryous** » 10 May 2005, 04:41

If you do this at night on a really bad engine, you can see the burning chunks of carbon come out of the exhaust. It looks like someone flicking really big chunks of burning cigarette ash out of the back of the car. I did this once with a MK1 Astra Diesel along a motorway in the middle of the night. Engine went from about 35HP to 55HP (it was only a 1.6D) in about 20 minutes. Continued boot-to-the-deck driving for the next week or so made it stop smoking quite so badly too! (oh, and 2 changes of oil.. it was beginning to resemble tar!)

JohnD · Post by **JohnD** » 10 May 2005, 23:31

My 2.1 Xantia has been smoke tested for the past five years on the same machine, and always at 80C. At 40K the reading was 1.1, at 52K it was 2.3, at 62K 1.8, at 75K 2.76, and recently at 88K 1.42. I always give it an oil and filter change with a week before the test, but I'm convinced that what accounts for the erratic results is (a) the quality of the diesel and (b) the amount of Redex/Dieselclean that I use in the period prior to the test.

citronut · Post by **citronut** » 11 May 2005, 03:08

a lot of diesel get potered around town most of the year,so get cloged up in combustion chamber and exhaust system most of the time they just need a good blast for a few seconds on rout to MOT,also diesel fiter freind said fuel adetives in diesels dose damage to hole system,as it is mostly abrasive regards malcolm

Mosser · Post by **Mosser** » 11 May 2005, 04:28

I have previously removed (just for the test) the air filter in a friends old diesel car after it failed the mot, put it straight back on the smoke tester and it passed with flying colours, and the filter didnt look at all dirty

bxbodger · Post by **bxbodger** » 11 May 2005, 04:37

At that sort of mileage if you've tried everything else it would probably benefit from an injector overhaul- they don't last for ever and should really be considered as a long service, but still consumeable part.
My BX started to get a bit smokey after 200000 odd miles so I put some recon injectors in and the difference was incredible-not a puff of smoke at any loading or speed, and a very good smoke test, going through on quick pass rather than the full repeated revvings- it even impressed the tester for its age!
On the old injectors the tips were eroded and the needles were protruding very slightly, and it only needs a small amount of wear at the tip and a bit of weakening of the internal spring to allow excess fuel through, and hence smoke.

JohnT · Post by **JohnT** » 11 May 2005, 23:20

There is a fuel additive called 'Forte' ( I think I got the name right)and it is superb. Put it in your fuel a few days before the retest, do a good run, and it will pass unless something really is requiring attention. This info came from my MOT tester I take my cars to.

stewart_c · Post by **stewart_c** » 12 May 2005, 00:52

Thanks for all the imput folks & I do appreciate the comments,it was the fact that the oil had only done 750 miles & I could not see how an oil change with an other new filter could make the difference.
However the main thing is it is on the road again for another year[:D]