My '06 V6 with 100m miles has an exhaust smell that is noticeable in the cabin while the engine is running, it seems more when the engine is cold. My first thought was that one or both of the exhaust manifold gaskets are bad, since the fresh air intake is adjacent to the engine compartment. When driving the car there is that characteristic compressive hissing you here on acceleration, usually indicative of (a) bad manifold gaskets. Since the block is aluminum and the manifolds assumed to be cast iron, it would make sense that any leakage is worse when the engine is cold.
My question is, has there been a problem with this generally in V6 Escapes? Is there another possible/historically common origin for the exhaust leak, maybe something like part of the EGR system?
Changing the exhaust manifold gaskets myself looks doable, though I'm sure it would be a thrash. Any thoughts would be appreciated.
Generally speaking, when an exhaust manifold gasket leaks, or the manifold is loose from the head due to broken or loose bolts, you will get a noise when the engine is running. It can be a chirp, whistle, or other spiky sound, especially if the manifold has a crack. The leak or crack can close up and quiet down a lot when all the parts are heated up.
If you don't have a noise, you don't likely have manifold gasket problems. I would look further down in the exhaust system, near the final catalytic converter or the 'flex hose' area.
I finally got around to removing the rear exhaust manifold as a process of removing a bad automatic transmission, which I have posted about elsewhere in this forum. Some of you know that to remove the transmission you have to remove the transfer case, and to remove the transfer case you have to remove the rear exhaust manifold, etc., etc. When I removed one of the six exhaust manifold nuts, the stud came with it. It appears that that cylinder was leaking because of the loose stud, and that is where the exhaust was probably escaping. Furthermore, the original exhaust manifold gasket is metal - not a great sealing gasket.
My questions are, would it be OK to put stud adhesive on the removed exhaust manifold stud to prevent it from loosening again? Also, is it OK to coat the new gasket in either that spray gasket adhesive, or a silicone sealing type adhesive? The replacement gaskets (Fel-Pro, etc.) all seem to have a composition design that isn't all metal.
It's pretty common for the stud to come out when removing and doesn't necessarily mean it leaked. Usually can tell by looking at the gasket. I've also seen the manifold itself leak around the flange. If you look at the manifold the flanges are welded to the actual manifold assy. I don't use anything on the new studs or gasket for adhesive and never had an issue. Did you ever hear an exhaust leak?
It would not hurt to put some loctite type thread locker on the stud, but it's likely not absolutely necessary. I don't use it much except when specified as a requirement.
The composition gaskets should make up for minor surface defects and seal much easier than the flat metal gaskets. I think I have bunches of the flat metal from 'other jobs' where I never took the manifolds off the heads.
Check the manifold flanges for flat using a straight edge from side to side and front to back or top to bottom. If you find any 'dips', at a last resort you can use a hammer to whang the flange bolt hole areas 'backwards' so they will tend to compress the remainder of the flange against the gasket before they too flatten in place. Gently gently.
Gentlemen, thank you for the comments. The sound made by what I assume to be the exhaust leak is a "spitting" sound I have found to be characteristic of manifold leaks in the past. The flex conduit after the manifold piping is pretty ratty, though I don't think that is the problem or would make that sound. I'm in MN and there isn't a final catalytic converter. I believe that is an add-on to meert CA emmision requirements. The sound and the smell arrived the same time to my recollection.
I looked at the manifold for cracks and gross breakage, but haven't checked for flatness. I will do that. My suspicion of the loose stud cylinder was based on what looked like exhaust gas discoloration around that port and under where the manifold was.
What about spraying/coating the new gasket in sealer - any harm in that?
I don't see any harm in sealer on the gasket. Still don't think I would use anything on the stud. I've seen way to many Brocken studs and couldn't imagine trying to remove one that has anything on them. Hopefully you don't ever have to remove it again but you never know.
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