Jeff Loughlin's exhaust manifold crack repair - Jeep JK Wrangler

How to Fix an Exhaust Manifold Crack With ThermoSteel


This was originally posted on I'm moving it over here so it doesn't get lost in cyberspace.

Most of us with the 3.8 engine will eventually have it: a crack in the exhaust manifold(s). Mine cracked on the drivers side around 80,000 miles. My passenger side is okay so far, but it's only a matter of time.

Anyway, I looked into replacing it, but the dealership wanted $450 to do it. You can buy the part for around $100 and do it yourself, but that's a lot of work, so I went looking for a quick, easy, and cheap solution instead.

I read about a product called ThermoSteel on another forum. ThermoSteel is an epoxy-like adhesive, and the manufacturer claims it can withstand temperatures up to 2500F. They also claim that this stuff is as strong as a hot weld. I have my doubts about that, but for $8 at AutoZone, I figured it was worth a shot.

It's not hard to do. The whole process took me about 20 minutes, and the hardest part was just getting the heat shield off. The bolts are very tight and rusted on, and the rear-most bolt is very hard to get to:

Manifold with wrench - Jeff Loughlin 1
The bolts are 10mm, and you'll need a U-joint and a long extension or two to reach the rear one. You might want to spray some penetrating oil on first and let it sit for a few hours or overnight, because yours are probably rusted on like mine were.

Just a note here about tools: buy good ones. Most cheap sets come with a 1/4" drive on the smaller sockets like the 10mm. The 1/4" drive ratchet handle that comes in the set won't be long enough to get the kind of leverage you'll need to get these bolts out. Do yourself a favor and buy a good set of 1/2" sockets and a good long ratchet handle to go with them. Trust me on this. The skin on your knuckles will thank me later.

The other two upper bolts are a little easier to reach. The lower bolt is tricky too, and there's not much room to work down there. You'll probably need the universal joint for that one too.

Manifold with wrench 2 - Jeff Loughlin 2

The heat shield is in two pieces, and they will come apart after you remove the bottom bolt (which is actually a nut - the bolt is mounted to the engine block). You'll probably want to remove the spark plug wires before you try to take the heat shield off, so they're out of the way.

Once you have the heat shield off, you'll see something that looks like this:

Huge crack in manifold - Jeff Loughlin 3

Now pick up your ThermoSteel and read the directions on the package:

ThermoSteel Package

The directions are pretty simple: Mix thoroughly, and smear it on. Make sure you mix it very thoroughly, as there will be a lot of gunk that has settled to the bottom. I used a flathead screwdriver to mix it up. When you're done, it should be about the consistency of toothpaste - if it's thinner than that, keep mixing.

Smear it on with a toothbrush (preferably someone else's) or your finger. The instructions say you can make it up to 1/4 inch thick, so put it on nice and heavy. If your crack is wider than mine (shut up), you might need to pack it down in there or use some wire mesh to cover it first. Mine was just a hairline crack, so I just smeared it all over the top.
ThermoSteel on Manifold - Jeff Loughlin 4

Let it cure for five or six hours. The instructions say you should heat the surface gradually after it cures, but you can't really do that with an exhaust manifold. I just started the engine and let it run for a minute or two, then shut it down and waited a half hour or so, then started it again. I repeated that three or four times and figured that was good enough. Then I reinstalled the heat shield and let it sit overnight before running the engine to full temperature.

That's all there is to it. Good luck. Mine's been holding up well so far. I'll update this if it ever fails, but it looks good so far.

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Last update: April 17, 2013