True CO2 output | Motoring discussion | Back Room Forum

Mon 16 Jun 2008 12:24

True CO2 output - Westpig

just had my car MOT'd. Examiner was kind enough to say that the readings on the Emissions test were very good, which is pleasing as the car is a V6 auto and only really used now in town....however, it is maintained properly via a Jag Independent, I only ever use BP Ultimate fuel and it gets an 'Italian Tune' roughly once a month

it has got me thinking though

would a well maintained so called 'gas guzzler' beat a poorly maintained smaller car on emissions?... or would a well built quality car beat a cheap one that tended to go out of tune more quickly? etc, etc

the figures for my 9 year old auto Jag S Type are as follows:

Fast Idle....
CO...............0.003% (limit <0.2%)
HC...............12 ppm (limit < 200ppm)
lambda.........1.008 (limit 0.970 - 1.030)

the car is too old to have the CO output on the V5, but a bit of research suggests that this car is shown as being 259 g/km

Will I be entitled to look a bit smug... or will I be shot down in flames and have to slink off back to the shadows with my shoulders down. I'm afraid my knowledge on this subject matter is somewhat lacking.

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Mon 16 Jun 2008 12:47

True CO2 output - Blue {P}

CO is Carbon MONoxide as far as I know, not Carbon DIoxide.

Sorry I can't be of more help as I don't know anything about it either!

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Mon 16 Jun 2008 12:52

True CO2 output - DP

The level of CO2 is a function of the amount of fuel burned. The more fuel burned, the more CO2 produced. This is why big cars are generally higher, small cars lower, and diesels lower still. CO2 emissions are given as an absolute level, so x grams per kilometre or other constant.

The MOT tests are a proportion or percentage. They do not take into account how much exhaust gas is produced in the first place, just what the gas consists of.

Bigger engines produce more exhaust gas than smaller ones, so for a given percentage of the total exhaust gas, the bigger engine is more polluting.

But it is possible that a well maintained, healthy "big engine" such as yours, can be less polluting than a smaller, badly maintained engine, or one with a fuelling fault.

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Mon 16 Jun 2008 13:48

True CO2 output - RichardW

But what's tested on the MOT bears no relation to the amount of CO2 the car is putting out - the emissions test is to check the engine is in tune and the cat and associated systems are working. All petrol cars (of a similar age) are subject to the same emissions levels in MOT test, but can have vastly different outputs of CO2 (like by a factor of 5).

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Mon 16 Jun 2008 14:46

True CO2 output - moonshine {P}

But what's tested on the MOT bears no relation to the amount of CO2 the

car is putting out - the emissions test is to check the engine is in

tune and the cat and associated systems are working. All petrol cars (of a similar

age) are subject to the same emissions levels in MOT test but can have vastly

different outputs of CO2 (like by a factor of 5).

Richard is spot on.

The MOT measures Carbon MonOxide

CO2 is Carbon DiOxide

Look to the MPG figures to get an idea of what cars produce the most/least CO2 per mile.

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