Oil change, pre smog test.

[wrcsixeight]

I see on that many websites concerning passing a Smog test, say that changing the Oil beforehand increases the chances of passing a Smog test.


I can't see this as increasing the chances by anything but a small fraction of a percent.

I've got to get a smog test within the next 2 months, and My oil certainly does not have enough miles or time on it to justify replacement.


I'm not stressing passing smog, as I've passed easily all previous times with usually decreasing numbers every 2 years. I'm just wondering how an oil change can realistically affect any of the pollutants the Sniffer, sniffs for.

Seems to me this 'change your oil recommendation before a smog test' just decreases the weight of one's wallet. If a person is stressing passing the Sniffer test, then that money is better spent on ignition parts rather than oil, IMO.

But perhaps there is something I have not considered.

 

[eljefino]

IIRC it was for the hydrocarbons, new oil soaks 'em up.

 

[147_Grain]

Fresh clean oil creates a better seal between the piston rings and cylinder wall, helping to improve emission levels.

 

[Chris142]

It works! It won't fix a gross puluter. It will make car that barely failed pass

 

[Chris142]

It works! It won't fix a gross puluter. It will make car that barely failed pass

 

[bdcardinal]

Yup, it will not help a ton, but if a car barely fails it will usually lower the numbers just enough to let it squeak by.

 

[BikeWhisperer]

I had a 1984 Chevy Scottsdale that was always on the edge smog wise. Twice it failed barely and twice I got the oil changed and nothing else, and it then passed.

Used oil vaporizes more hydrocarbons through the PCV system and fresh oil can be just enough to lower your HC levels.

 

[panther427]

Yes what they said. It really does work. used to do emission at my old work. If it was really close we would recommend a oil change. And like a miracle and to the happy smiles of customer it would work. Never really thought about the science behind why

 

[supton]

Originally Posted By: 147_Grain
Fresh clean oil creates a better seal between the piston rings and cylinder wall, helping to improve emission levels.


This I could buy. But

Originally Posted By: BikeWhisperer
I had a 1984 Chevy Scottsdale that was always on the edge smog wise. Twice it failed barely and twice I got the oil changed and nothing else, and it then passed.

Used oil vaporizes more hydrocarbons through the PCV system and fresh oil can be just enough to lower your HC levels.


Over in the DI thread someone has the idea that changing oil too soon causes too much "new" oil vapors to into the pcv system. I'm not sure how or if that correlates.

Not saying you are wrong, just not sure how that plays with the DI issue.