Emissions and motor oil / What can you tell from a cars exhaust smell ?

[Cd]

Dumb question of the day :

My car exhaust smells like motor oil ( a sweetish smell ) just after an oil change, but after short while ( 250 miles ) it begins to smell like regular car exhaust.

I would think that the car produces less emissions with fresh oil, but is this the case ? My cars exhaust is pretty strong now, but the oil is still a dark honey color.

What causes a stronger exhaust smell ? Is it a sign that the oil is breaking down, and producing more emissions ?

Also, is synthetic motor oil better for the environment ? What about just using recycled motor oil ?

" The Lesser of Two Evils
Conventional motor oils are derived from petroleum, whereas synthetic oils are replicas manufactured from chemicals that are really no kinder to the environment than petroleum. As such, conventional and synthetic motor oils are about equally guilty when it comes to how much pollution they create. "


Source : Motor Oil -- Synthetic or Conventional Motor Oil -- Which is Better for the Environment?

Lastly, read the first line of the text on this bottle of Valovoline NextGen oil :

" oil doesn't completely wear out ( it simply gets dirty ) "



So what else cause a strong exhaust smell ?


Thanks !

[JRMichler]

Most likely is that a couple drops of oil landed on the exhaust manifold or exhaust pipe.

[Gasoline Fumes]

When I change the oil on my Honda, a lot of the oil from the filter ends up on the exhaust pipe and CV axle.

[Cd]

Originally Posted by JRMichler

Most likely is that a couple drops of oil landed on the exhaust manifold or exhaust pipe.

If you mean the sweetish oil smell, it comes out the exhaust pipe that way, and this happens each and every time the oil is changed. Open up a new bottle of oil and take a whiff. That is what I smell.

[user removed]

I can smell a bad oxygen sensor or head gasket following a car on the highway. A cold engine smells different before the catalyst lights off. I never smelled a difference between fresh oil and old oil after an oil change.

regards
mech

[JRMichler]

That honey color, even in new oil, is dirt. Clean oil is transparent. I once designed a hydraulic system and specified a three micron absolute, full flow, no bypass, high collapse element. After running 18 months without an oil change, the analysis said the oil was good for continued service. When I looked in the reservoir, I could see the bottom through about 20 inches of perfectly clear transparent oil. That's why oil added to industrial hydraulic systems, even from a new container, is supposed to pumped in through a filter.

Motor oil has additives to counteract acids from blowby. Those additives get used up.

If you had an engine with really good filtering, analyzed the oil regularly, and added additives as needed, you could run the same oil forever. It's cheaper to just change the oil, though.

[Cd]

If i pull my spark plugs. there is oil leaking down the threads of the plug - pretty bad too on at least two.
I changed the gaskets, but i still have the issue.
Since i am screwing in the plugs, this seals the hole and keeps any oil from entering the combustion chamber though - correct ?
That's the only thing that I can think of that would make the exhaust smell like oil.

So if I were to run an engine with new oil, versus old oil, the emissions will be worse with the old oil ?
If so, why is this ?

What exactly causes an engine to produce more poison emissions ?

"Motor oil has additives to counteract acids from blowby. Those additives get used up.

If you had an engine with really good filtering, analyzed the oil regularly, and added additives as needed, you could run the same oil forever. It's cheaper to just change the oil, though. "

So if I understand correctly, an engine will produce more emissions once additives in the oil are used up ?

[ksa8907]

Install an oil catch can aka an oil-air separator in the pcv system. My guess is that after an oil change the oil level is high enough that excess oil gets sucked into the intake.

One way to verify is to pull the intake or you could look for oil buildup on the throttle body.

[JRMichler]

Originally Posted by Cd

So if I were to run an engine with new oil, versus old oil, the emissions will be worse with the old oil ?

So if I understand correctly, an engine will produce more emissions once additives in the oil are used up ?

New vs old oil does not affect the emissions. New vs worn engine does affect the emissions.

Old oil has dirt in it. That dirt acts like grinding compound and causes engine parts to wear out faster. When the additives are used up, blowby reacts with the oil to make acid, which also causes engine parts to wear faster.

[user removed]

Originally Posted by Cd

If i pull my spark plugs. there is oil leaking down the threads of the plug - pretty bad too on at least two.
I changed the gaskets, but i still have the issue.
Since i am screwing in the plugs, this seals the hole and keeps any oil from entering the combustion chamber though - correct ?
That's the only thing that I can think of that would make the exhaust smell like oil.

So if I were to run an engine with new oil, versus old oil, the emissions will be worse with the old oil ?
If so, why is this ?

What exactly causes an engine to produce more poison emissions ?

"Motor oil has additives to counteract acids from blowby. Those additives get used up.

If you had an engine with really good filtering, analyzed the oil regularly, and added additives as needed, you could run the same oil forever. It's cheaper to just change the oil, though. "

So if I understand correctly, an engine will produce more emissions once additives in the oil are used up ?

If you have oil accumulating on the spark plug threads, it is either coming past the rings or valve seals, or it is leaking out of the valve cover gasket and pooling in the recesses where the spark plugs are located.

The second scenario is in engines where the plug is located in a recess surrounded by the valve cover with a cup and gaskets to seal off the plug and cup.

The threads on the plug, being located below the crush washer can only accumulate oil from the combustion chamber. When we changed plugs that were through the valve cover, as well as most any others, we blew the recess out with air to get any accumulation of oil and dirt out before removing the spark plug to prevent the accumulated debris from falling into the combustion chamber with potentially disastrous consequences.

The type of engine and the oil consumption would help with any diagnosis, but regardless of the type there is oil consumption and that is what you are smelling. It's also the most likely scenario that produces the smell you describe. Most likely the catalyst's function has deteriorated due to oil contamination which also produces the"sweet" smell you describe.

Why it would be more prevalent with fresh oil?

Not sure on that one, but I can smell them on the highway. One exception is leaking valve cover gaskets which can fill the spark plug recesses with oil as well as leaking onto the exhaust manifold. Sometimes I can see the smoke from the burning oil when the car is sitting at a light idling.

regards
mech