Just blowing hot air?

December 17, 2009 7:56 PM

Does this manifold on a 2.5L Jeep really expel hot air into the main engine compartment or is a part missing?

If you look at the picture, the side facing away from the screen joins onto the engine. The output on the bottom right presumably joins onto the exhaust pipe/system, but what about the output middle-left, pointing out to your screen?

Background: I'm borrowing a Jeep at the moment, and it makes one hell of a racket-- I heard it had some work done on the manifold recently, so I had a quick peek to see if there was anything immediately loose/etc. I noticed that there's an outlet from the manifold that goes no-where, just expels air into the engine compartment-- this (as a total non-mechanic) strikes me as weird.

Has a part fallen off, or was forgotten to be placed on, or is it working as designed and the noise is born from something else wrong with the new manifold?

posted by Static Vagabond to travel & transportation (5 answers total)

Usually that kind of fitting on an exhaust manifold has a pipe attached that goes up to the air cleaner/air intake. It isn't actually a big hole in the manifold that lets exhaust and noise out, it's kind of a shroud around the manifold that sucks fresh air past it to heat it up.
posted by FishBike at 8:29 PM on December 17, 2009

IT is usually hooked up to a fitting in the intake manifold that heats up the carburetor and shortens warm up time.
posted by bartonlong at 8:42 PM on December 17, 2009

It should have a pipe connected (usually) to the underside of the air cleaner assy.
posted by Duke999R at 8:44 PM on December 17, 2009

As others have said, the outlet facing you in the picture directs hot air (not exhaust) to the air cleaner through a duct or pipe. The air cleaner has a valve that opens when it's cold and closes when it's hot, so it helps the engine warm up faster. Not a huge problem if the connection between the manifold and air cleaner is missing -- it just means the car will take a little longer to warm up.

As for the noise -- you mention the manifold was worked on recently. My money would be on either that the manifold gasket wasn't torqued down right (you usually need to follow a specific pattern, generally tightening from the "inside" bolts out, and may need to retorque after it's been through a few heat cycles) or that the connection between the manifold and exhaust pipe is loose.
posted by zombiedance at 9:35 PM on December 17, 2009

It did turn out to be the exhaust manifold to exhaust pipe connection. I had a look under the engine on the weekend and found the connection point which was indeed loose, so I borrowed a socket set, tightened it up and it's purring like a kitten now— huge difference.

Thanks for all the help, perhaps because I'm in a hot climate we don't really have the need for the hot air to get passed back into the intake manifold?
posted by Static Vagabond at 10:15 AM on December 21, 2009