Vapor from engine..... What is it?

[WMSmotorhead]

Ok, 2001 Ford Zetec motor... a hot little iron block.

If the motor is hot, and I remove the oil fill cap, a bit of vapor will rise up from it... looks like a waft of steam.

What is it? It's done it for over 100K miles, so I assume it hurts nothing. Just curious about it.

 

[Steve S]

That is called blow by it is what gets past the piston rings from the combustion process [blows by the piston rings] and there also a bit of oil vapor but mostly it is blow by. Before emission controls started taking effect the blowby was vented into the atmosphere via what is called a road draft tube . Now it plumbed back into the intake manifold and usually the location depends upon the Manufacture. Positive crankcase ventilation,,PCV valve

 

[Bluestream]

If it comes from the oil cap, then its just oil vapours, no big deal

 

[TFB1]

It's a bit of blow by, no big deal... If it were actually oil vapor, the engine would be a heavy oil user due to the PCV valve sucking in the vapor...

 

[OldCowboy]

Actually, under SM and SN ratings, up to 15% of oil can boil off during use. This is known as the NOACK Volatility.

 

[Errtt]

Yup blow-by. Not to worry unless there is a high fuel dilution and/or PCV system isn't working.

^^^ I remember the days of the draft-tube. And I was always checking and/or cleaning the screen on the valve cover vent cap. The good ol days. Liked the fuel sediment bowl on my 1st truck too.

 

[cmf]

Originally Posted By: OldCowboy
Actually, under SM and SN ratings, up to 15% of oil can boil off during use. This is known as the NOACK Volatility.


The current (SL onward) NOACK volatility test is the ASTM D 5800 which is the Selby-Noack volatility test. The temperature used for this is 250 degrees Celsius (482 Fahrenheit). I don't think it's really applicable to this scenario.

As others have said, it's blow-by and definitely nothing to worry about.

 

[Gene K]

Look under large trucks idling sometime. They still have road draft tubes.

 

[ltslimjim]

Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?

 

[Bluestream]

Originally Posted By: TFB1
It's a bit of blow by, no big deal... If it were actually oil vapor, the engine would be a heavy oil user due to the PCV valve sucking in the vapor...


Blow by is mostly oil vapour

 

[A_Harman]

Blow-by gases are mostly products of combustion that blow through the ring end gaps. They are mostly carbon dioxide and water. What you see is the water vapor. The other stuff that you see will oil mist from crankcase churning.

 

[TFB1]

Originally Posted By: Bluestream
Originally Posted By: TFB1
It's a bit of blow by, no big deal... If it were actually oil vapor, the engine would be a heavy oil user due to the PCV valve sucking in the vapor...


Blow by is mostly oil vapour


IF it were actually oil vapor we'd be adding a quart or two a week to our engines... Think about it, you pour a gallon of water into a vaporizer and it's gone in less than 24hrs... No oils aren't water but vapor is vapor and would indicate the oil was boiling off...

 

[chevrofreak]

Fuel and water, with some oil. For every gallon of gasoline burned, over 1.25 gallons of water is created. Some of it makes it past the piston rings as blowby.

 

[Jeff_in_VABch]

Get yourself a crankcase vacuum pump and you can get rid of all that blowby and gain quite a bit of horsepower.

I beileve as engine technology marches on, production cars in the future will use crankcase evacuation. If we are still using gasoline.

I have seen up to 40HP power increases on some of my engines at 15" crankcase vacuum. And nice clean oil.

 

[Gene K]

Originally Posted By: ltslimjim
Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?


The reason for the road draft tube is the flow of air past it creates a pressure differential which helps evacuate the crankcase improving ring seal.

 

[lexus114]

Originally Posted By: Gene K
Originally Posted By: ltslimjim
Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?


The reason for the road draft tube is the flow of air past it creates a pressure differential which helps evacuate the crankcase improving ring seal.




Yup, What he said! ^^^

 

[WMSmotorhead]

I never figured it was anything to worry about. I never checked my other cars for it, but I bet they have a little bit too. I'm glad to have an explanation. Around here I was waiting for questions about what oil is in there, what my UOA was, etc...

Its got some WPP in it.. and I havn't had a UOA on it since I bought it 115K miles ago...

If anyone ever wondered if WPP's oil was OK... I have cars that have gone 50-100K miles on it with no known issues related to oil. I like the pricing on it.

 

[ltslimjim]

Originally Posted By: Gene K
Originally Posted By: ltslimjim
Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?


The reason for the road draft tube is the flow of air past it creates a pressure differential which helps evacuate the crankcase improving ring seal.


So, basically back pressure making for a better 'seal' for each stroke to TDC for each cylinder. Almost like a safety net or required for operation period? Just curious.

 

[Jeff_in_VABch]

Originally Posted By: ltslimjim
Originally Posted By: Gene K
Originally Posted By: ltslimjim
Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?


The reason for the road draft tube is the flow of air past it creates a pressure differential which helps evacuate the crankcase improving ring seal.


So, basically back pressure making for a better 'seal' for each stroke to TDC for each cylinder. Almost like a safety net or required for operation period? Just curious.


You want a negative pressure in the crankcase, not positive. However, this is not implemented in but a very few vehicles engines but in all race/performance engines.

 

[uart]

Originally Posted By: lexus114
Originally Posted By: Gene K
Originally Posted By: ltslimjim
Interesting, is a road draft tube similar to the 'purge' that happens at the bottom of the charcoal canister that allows the heavier fumes to escape out the bottom of the engine bay?


The reason for the road draft tube is the flow of air past it creates a pressure differential which helps evacuate the crankcase improving ring seal.




Yup, What he said! ^^^

Yes the small negative pressure will aid in the extraction of crankcase fumes, but I don't believe that this small level of negative pressure will have any meaningful effect on ring seal.