Why is half my gas tank cover colored like this?

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So I know I have to replace the center muffler in my LX, so I was under there looking at the flex pipe and rear muffler to see if they needed to be replaced too, while I was under there. I noticed that half my gas tank seems to have what kind of looks like soot on it, but only half. It's kind of behind the flex in the flex pipe, but I can't see any crack in that pipe. It's dry, doesn't look like oil either.

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awesomeissquid

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My money is on exhaust leak in the area. Notice how the cross member above the flex pipe is also darkened.
 
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That was my first thought. But I also have the infamous ticking exhaust manifold. The ticking goes away after a minute or so, but could this be exhaust from the manifold leak? Or is the leak just on the top side of flex pipe.
 

awesomeissquid

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You sure it’s the manifold and not the timing chain tensioner? Mine ticks on cold start but does away after a couple minutes.
The 100 series does not have a timing chain.
 

awesomeissquid

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That was my first thought. But I also have the infamous ticking exhaust manifold. The ticking goes away after a minute or so, but could this be exhaust from the manifold leak? Or is the leak just on the top side of flex pipe.
I think if it was the exhaust manifold you would have the same coloration all the way from the front of the engine. It’s possible, but from the image it looks like it starts right behind the transfer case.

Also if the ticking stops once warm, that would mean the hole is sealed up once it warms up.

Best way to confirm where you have a leak would be to take a shop vac and connect the hose to the exhaust to positively pressurize the exhaust pipe. Then spay some soapy water and look for bubbles.
 
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Likely your gas tank skid, at some time in the past. Had a corrosive splashed on it. i.e salt water, mag-chloride, etc.
The dark area of frame above spider (AKA U-joint). Is from lubing spider (due every 5K miles) and the area gets dark with caked on with grease Yours looks under greased, by picture, But pic is not clear (shadowed).

Not likely a leak in the exhaust Y pipe. If there is, it should be easy to spot.

Ticking concerns:
Putting your ear in fender well during cold start up. Helps find if tick from engine bay area and which side or sides.
Driving by a wall or stand at curb as someone else drives away, after warm up. Helps determine if actually stops ticking after warm up.
Ticking sound may be exhaust manifold leak. We don't get "to concerned", if that what it is,. Until tick does not go away once warmed up. As exhaust leak can get into cabin, and if before or at a CAT, can damage CAT.

Ticking can also be from a spark plug walking out. This we must take care ASAP! Easy thing is to start by replacing spark plugs. I torque to 18ft-lbf (Toyota spec is 13ft-lbf) in hopes of slowing walkout of spark plugs. If tick goes away after plugs replaced, you're golden.

 
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awesomeissquid

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Weird. Not sure how I ended up in the 100 section. Sry - that I was in the 200 forum
No worries. You had me second guessing myself for a second.
 

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