Whatt Does The 'valve/flap' Do In My Air Intake Tube?

[hoorders]

Just did a tune up on my newly aquired 93 yukon that has the 5.7 in it and I noticed there is a valve/flap looking thing in the air intake tube. Right below this a tube connects and goes down to ontop of the exhaust manifold.

 

What does this do and how do I know its working properly?

My concern is that it could stay shut closed all the time starving the engine of air.

Can I rig it to just stay open, will this screw anything up?

 

I noticed when I pulled the lid off the air breather the bottom of the lid was spattered with gas....could this have to do with that valve thing?

 

Thanks.

[dewfpo]

The flap valve you are referring to heat the intake air when the engine is cold. Once the engine warms up to a certain temp, the air flap valve closes and you only draw air in from the cold side of the intake. It does not limit air, it diverts air from one source or the other (hot or cold). The valve should be close when the engine is up to operating temperature.

 

I have no idea where the gasoline is coming from. Are you sure it's gasoline?

 

DEWFPO

[dlewis1111]

The flap valve you are referring to heat the intake air when the engine is cold. Once the engine warms up to a certain temp, the air flap valve closes and you only draw air in from the cold side of the intake. It does not limit air, it diverts air from one source or the other (hot or cold). The valve should be close when the engine is up to operating temperature.

 

I have no idea where the gasoline is coming from. Are you sure it's gasoline?

 

DEWFPO

 

+1 used to be called a thermac valve

[hoorders]

The flap valve you are referring to heat the intake air when the engine is cold. Once the engine warms up to a certain temp, the air flap valve closes and you only draw air in from the cold side of the intake. It does not limit air, it diverts air from one source or the other (hot or cold). The valve should be close when the engine is up to operating temperature.

 

I have no idea where the gasoline is coming from. Are you sure it's gasoline?

 

DEWFPO

Makes sense.

Can these malfunction?

What controls for how long it stays open until it closes?

 

Thanks.

[dlewis1111]

The flap valve you are referring to heat the intake air when the engine is cold. Once the engine warms up to a certain temp, the air flap valve closes and you only draw air in from the cold side of the intake. It does not limit air, it diverts air from one source or the other (hot or cold). The valve should be close when the engine is up to operating temperature.

 

I have no idea where the gasoline is coming from. Are you sure it's gasoline?

 

DEWFPO

Makes sense.

Can these malfunction?

What controls for how long it stays open until it closes?

 

Thanks.

 

 

Yes they can malfunction. On older vehicles there was a heat sensitive coiled spring that moved the flapper based on the temp of the metal. I have seen some that are also vacuum controlled too. If the diaphram gets a hole in it, it will not work right either. Not working right will result in taking a little longer to warm up the engine, or constantly drawing in hot air from the tube

[Bob D]

Can these malfunction?

Yes, but rarely.

What controls for how long it stays open until it closes?

My (slightly older model) thermac is controlled by vacuum triggered by thermostatic switch on intake man. I believe flap is "normally open". Vacuum (when cold) closes flap. Engine hot kills vacuum, flap opens.

Very easy to diagnose.

Look down snorkel when engine cold. Flap should be closed. Disconnect vacuum line, flap should open. Reconnect vac. line. When engine reaches operating temp. flap should open.

[hoorders]

Can these malfunction?

Yes, but rarely.

What controls for how long it stays open until it closes?

My (slightly older model) thermac is controlled by vacuum triggered by thermostatic switch on intake man. I believe flap is "normally open". Vacuum (when cold) closes flap. Engine hot kills vacuum, flap opens.

Very easy to diagnose.

Look down snorkel when engine cold. Flap should be closed. Disconnect vacuum line, flap should open. Reconnect vac. line. When engine reaches operating temp. flap should open.

 

I dont beleive mine is vacuum controlled, but I can certainly do the same check when engine is cold then hot.

 

Thanks.

[Bob D]

 

 

..thermac is controlled by vacuum triggered by thermostatic switch on intake man...

Not so. (Gotta correct myself) Temperature sensor inside the air cleaner modulates the vacuum to the snorkel vacuum motor.