What is the best way to check for the exhaust manifold leak--a stethoscope?
The first thing to do is check it when the engine is cold. When it is cold the metal shrinks and if it is leaking, it will leak more. Also, since it's cold you can feel around with your hands. Start it up when it's cold, feel with your hands and listen with your ears. A lot of times, you will feel the leak coming out.
If it is a small leak and you can't really feel it and can hardly hear it, you can do my trick "Finding Engine Vacuum Leaks With a Cigar". You can take out the oxygen sensor that's near the manifold and you can blow smoke into that. Wherever you see the smoke coming out, you know that's where the leak is.
You can take off one of your vacuum lines, like a vacuum line to the brake booster, and you can spray a little bit of carburetor cleaner in there. This will make the engine smoke and you'll be able to see smoke coming out of the exhaust. This will also allow you to find the leak. I do this a lot of times when it is hard to find a certain leak.
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