Like many of you out there with the 4.0 I6, high-under hood tempuratures are a factor in the overheating of your engine, resulting to shortened engine life and frustration with your Jeep! This problem has lead to undesired modifications such as finding a place to add another electric fan, or even worse, cutting holes in your hood for hood louvers to let the hot air escape! There is an easy, effective, cost efficient fix to this problem all together- just don't let the heat happen! The stock 4.0 Exhaust manifold is a pretty easy item to tackle. In this Write-up I will show step-by-step procedures, along with a total cost of supplies and time frames of engine down time.
Starting out- Pulling off the exhaust manifold comes off pretty easy. The Intake manifold and the Exhaust come off of the engine in one complete assembly. Disconnecting vacuum lines first, amd the air filter assembly, along with fuel and wiring harness gives you access to the bolts holding the manifolds to the engine block, after removing the bolts, you should end up with something like this-
Undo the metal tube going into the bottom of the EGR valve (the tube holding the Exhaust to the Intake, and it will separate itself. My exhaust has its fair share of Oxidation (Corrosion due to heat and gases, commonly mistaken as rust) but overall, its in good condition, no holes, no cracks, just brown!
Remove the O2 sensor, and for best results you should sandblast the exhaust. I had access to a sandblaster with 40 grit sand (removes material very quickly) but quotes from local shops were around $10-20 but its well worth it in the end. After sand-blasting it will look like this.
Now for Coating. There are a few different options out in the market. If this was going to be a show-rig I would opt out to have http://HPC.com (located in Utah) coat it with their ceramic but that just wasn't in my budget so I chose the rattle can method bought at the local car-parts store. (Different colors available such as Black, Dark Grey, Flat aluminum, Red and White, along with Different heat ranges from 1000 degrees to over 2000.) I Chose the Flat Aluminum, during painting I had to be cautious to make sure that I covered every surface because the paint color was almost the same color as the metal after sandblasting. All finished painting-
As per direction on the Ceramic Coating rattle can, the exhaust needed to be baked at high tempuratures to cure the coating and to make it chemical resistent. A local Powdercoating shop baked it per directions on the can for $20 and took one night.
Reduce Under Hood Temps- Exhaust Wrap
Now it was time for the pipe wrap, as I understand the Ceramic coating helps retain the heat inside the pipes versus no coating, but I wanted to go a step farther to really keep the heat inside my exhaust, and not inside my engine bay. Most car part places should carry the supplies you need. My options were some 2" wide black tape and some 1" wide cream-colored tape. although I would have preffered black, I thought the 2" wide tape might be a little more difficult to work with the sharp bends so I purchased the 1" wide tape. Along with some Stainless Steel locking ties (like plastic cable ties, but wont melt! and beware, these things hold together and do not release! so don't push the end of one in thinking you may be able to get it undone, I Found out the hard way. I also purchased some Silicone spray to go over the tape after it was all wrapped to help aid in the chemical resistance and durability of the tape itself.
Starting wrapping- Following instructions provided with the tape, I measured and cut strips of the tape and soaked them in water to loosen up the fibers of the tape and make them more pliable. Here are the lengths of the strips I cut. Cyl 6- 85"... Cyl 5- 70"... CYL 4, 3, and 2, - 63". and Cyl 1 was left uncut of the rest of the roll to make sure I had enough to complete the project. Start at the upper side of the exhaust (towards the engine block) and work your way towards the collector, wrapping very tightly (tighter the better as it is less likely to come unwrapped) and overlapping the previous wrap about 1/4". Here are pictures of cylinders 6 and 5 wrapped (before I soaked the wrap in water to make sure I had enough to reach main pipe)
After I was sure I had cut the strips long enough I unwrapped them and soaked them in water for a few minutes, and started wrapping, starting at cyl 6 and working towards cyl 2. remembering to wrap very tightly.
All Cylinders are wrapped now except for number one and the main pipe as I will be doing them with one solid peice of tape.
And finally, wrap cyl 1 and the main pipe starting at the flange closest to the engine block, and working your way down to the collector making sure to overlap all of the ends of the other cylinder pipes to keep them from coming undone. Use the Stainless steel locking ties on the ends of all tape to keep from unraveling and you will end up with a finished product like this! Your color may vary but if done correctly it will drastically decrease your underhood tempuratures, aiding in the overheating problem.
Wait for the wet wrapping to air dry and reinstall the manifolds back onto your engine! Here is a cost breakdown, your cost may vary slightly depending on access to a sandblaster and cost of supplies.
Ceramic Exhaust Coating- $6
Baking and Curing coating- $20
Pipe Tape- 29.99 (for 50' roll. I had about 2' left over)
Stainless steel ties- $5 for a 8 pack.
"Optional" Silicone spray- $7
Total- Should cost you around $70. And can be done in 2 days.