Exhaust manifold replacement?
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Freshman User
Joined: Jun 2003
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Exhaust manifold replacement?
I have an 89 f150 351w. I appear to have an exhaust leak right @ the manifold flange. In fact I can feel the leak. Brought it to the shop and they say that they need to replace the whole manifold. Does this sound right?
Posting Guru
Joined: Dec 2002
Posts: 1,297
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From: Billings MT
Exhaust manifold replacement?
Those manifolds are usually cast steel. Welding cast steel does not always hold. It is best to replace the manifold, that is if it is cracked. If you don't see any cracks, replace the gasket and see what that does.
You might want to look into headers, as sometimes it is cheaper to buy aftermarket headers than one manifold.
You might want to look into headers, as sometimes it is cheaper to buy aftermarket headers than one manifold.
Elder User
Joined: Aug 2001
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Exhaust manifold replacement?
You won't be able to tell visually if it is warped. We're talking about a few 0.001" over the length of the manifold. When it is off the engine, hold a steel straightedge against the manifold. If you see light in places but not others, or if you can slip a piece of paper under the straitedge, then it is warped. If the manifold isn't cracked, a machine shop can grind it flat so it is as good as new. The service shop probably wants to replace with a new manifold because they don't want to tie up their service bay for several hours while the part is sent out to be ground.
Senior User
Joined: Mar 2003
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From: NE TX
Exhaust manifold replacement?
Replaced exhaust manifold on 1997 F350 5.8 for $113+gasket. Both had been changed before I bought it. Look for cracks. They are easier to see when it is hot. My manifold came with flange on it (F350 had larger flange than F150 for some reason, F150 is slightly cheaper). 1980's models (carburated) had donut shaped gaskets between the manifold and pipe. This manifold has it built in, so if there is damage to the mounting surface (pipe end) the manifold may need to be replaced or repaired. I've had prices as low as $90 for aftermarket so it is probably cheaper to replace than repair. Headers are not that cheap and may not last as long. If the leak is at the flange to pipe, try replacing the studs and using a high temp sealer, spray graphite lube, or anti seize to coat the surface. Depending on the size of the leak, this might work. I've used red silicone with successs but doesn't last long on farm diesels. I wouldn't suggest it on this because of higher temperatures. Check if the pipe flange has been bent by misalignment/overtightening.
