Sniff test doesn't work

[stilldesperate]

I've just called to the local MOT garage for it doing.

The owner said that it's not worth doing on diesels, as what the meter looks for is gasses, (which are present in petrol engines if the head / gaskets gone),
but in diesels they are particles (I understood this to mean "solids" in the coolant).

Discuss

SD

[francophile1947]

Sounds like a load of old squit to me - I'm sure I get gas out of my exhaust pipe , not solids, and that gas could get into the coolant if there is a gasket/head problem.

[stilldesperate]

I thought the same, John, but thought I'd air it on the forum.

If you can measure co2 with the meter out of the exhaust, then surely it's the same if it's in the coolant

Trouble is, you can't argue with a man convinced!

SD

(please note, the term "man" is not intended to be gender specific. In fact i wouldn't dream of trying to change a womans mind )

[francophile1947]

(please note, the term "man" is not intended to be gender specific. In fact i wouldn't dream of trying to change a womans mind )

Coward

[mikeonb4c]

This rings a bell. Wasn't there discussion on here a long time back about it being hard to kill yourself in a diesel if the exhuast leaked fumes into the cab. Was that because you don't get the same problem with noxious (carbon monoxide - CO - gas)? If the sniffer measures CO (which another ringing bell tells me could be likely as CO, being more reactive, is easier to design sniffer systems for) then putting it all together might provide a case for sniffers not working too well on diesels.

But the above is all hypothisesing - it'd need checking out either way

[helen&tony]

Hi
No...a diesel engine doesn't pollute, and the exhaust produces nothing but eau de cologne and clean mountain air...that's why they never test the emissions for the MOT
Yes...diesels do produce Carbon Monoxide, but less than a petrol motor...they also throw out particulte matter and nitrogen-based gases
Whether the levels have to be high for a sniffer test to work, I have no idea.
Cheers
Helen

[dandywarhol]

tell your "mechanic" that the sniff test is to check for combusted CARBON DIOXIDE (CO2)

If he's still not convinced, then show him this..................
http://www.justoffbase.co.uk/Combustion ... ley-VS0061

[stilldesperate]

Interesting - I just phoned another MOT tester and they don't think it would work either

For diesels, they use an opacity tester - shining a light and measuring how much light is received. This wouldn't work in the header tank.

He didn't think the petrol engine "probe" would work in the header tank either........

Has anyone actually had a test prove a head/gaskets gone?

SD

PS - Yup, Cowardly

[dandywarhol]

aye

[rita]

aye

Hi,
Can you remember what the readings were.

[dandywarhol]

Sorry - it was a while ago but as soon as the gas analyser probe "sniffed" the steam the CO2 level rose. It was on a Citroen BX1.9 and about 14 years ago.........................

[stilldesperate]

.... That's proof enough for me !