Why would changing motor oil to fresh oil before inspection be helpful?

[JT20]

I have heard of this. To change the oil to fresh oil before you get the car inspected. I can't for the life of me think of why that would help.

What is the deal with that? (And has anyone else ever heard this advice. Same as, say, put Premium gas in it before you go.)

All they do on 1996 and newer cars is read the OBD2 so I am suspicious of why changing the oil would help... This is gonna be on a 2004.. I am locked in familial debate about this as we speak, thought I would get an answer.

Let's assume emissions check.

 

[Anduril]

It would only (possibly) matter if they tested tailpipe emissions.

 

[Trav]

It would possibly only help with tailpipe testing if the oil had fuel dilution otherwise if all the monitors have run and no CEL it will not make any difference.

 

[AutoMechanic]

I don’t know. We don’t do emissions tests in my part of the state I’m in. Only the northern part of the state does the emissions tests. That’s the only reason I could think of it.

 

[zzyzzx]

Does anyplace do tailpipe testing on OBDII vehicles?

 

[JT20]

Does anyplace do tailpipe testing on OBDII vehicles?

If they don't exempt 1995 and prior vehicles? Yes.

 

[1uz_4me]

Does anyplace do tailpipe testing on OBDII vehicles?

Good ole California

 

[zzyzzx]

Good ole California

I'm adding this to my long list of reasons not to move to California.

 

[Imp4]

I'm adding this to my long list of reasons not to move to California.

Too much honesty?

 

[DGXR]

I could see a difference if the new oil is a lower viscosity (0/5w20) and the vehicle requires a sniffer (emissions) test. But even then, this would only be needed if there was a reason to believe the vehicle will not pass the sniffer test. And in that case it needs proper repairs, not thinner oil.

 

[Andrew1972]

Old wives tail. People who did it and it failed will never admit it. Irrelevant.

 

[pezzy84]

If this is just a OBD2 plugin emissions check its not gonna make a lick of difference whether oil is fresh or has 20k miles on it (well unless the neglected car gets a CEL due to neglect).

We have a similar annual emissions check in our area and it involves an OBD2 plugin, they test the gas cap separately then mirror under the car to make sure the cat is still intact. Its been a few years since I have had to get one done (diesels are exempt) but honestly I don't think any of them even popped the hood.

 

[blupupher]

Can't think of any reason to do this.

 

[atikovi]

Old wives tail. People who did it and it failed will never admit it. Irrelevant.

If you ever do an oil change on an older car or one that hasn't had the oil changed in a long time, take a whiff of the drain pan. Likely get a strong gas smell. Good old hydrocarbons. And what does a tailpipe test check for? Excess hydrocarbons.

 

[el Nuke]

If I owned a shop that did oil changes and state inspections, I would try my hardest to get this rumor circulated in my area. Every little bit helps!

 

[atikovi]

If I owned a shop that did oil changes and state inspections, I would try my hardest to get this rumor circulated in my area. Every little bit helps!

Because shops really clean up on all those $19.95 oil changes?

 

[el Nuke]

Because shops really clean up on all those $19.95 oil changes?

I’m sure I would charge more than $20, but the actual price of my imaginary oil changes doesn’t matter, for my shop is imaginary...just like the premise behind this thread.

 

[kschachn]

If you ever do an oil change on an older car or one that hasn't had the oil changed in a long time, take a whiff of the drain pan. Likely get a strong gas smell. Good old hydrocarbons. And what does a tailpipe test check for? Excess hydrocarbons.

The tailpipe test checks the tailpipe, not the oil pan. Does the emissions test facility stick their probe down the dipstick tube?

That's the part I struggle with, what connection there is between emissions testing of the exhaust and how that's influenced by the oil. Even "bad" oil.

 

[Jetronic]

All cars here get a physical sniff test. Lambda value has to be withing the 0.997/1.003 range and CO has to below a threshold depending on the first registration date. 2% for old non catalysed cars I think. 0.35% for recent cars. some at idle, some at higher rpm...

Diesels get revved to redline and the opacity of the exhaust gas gets measured.

 

[Le_bow_ski]

I'm adding this to my long list of reasons not to move to California.

No doubt there are millions of Californians who‘s highest aspiration in life is to move to Baltimore, Maryland.