The Air Filter on a 2004 Jeep Wrangler TJ 4.0L 6 Cylinder

This picture has the air filter high-lighted in yellow, the fuse box in red, and the alternator in light blue. This is a picture of my Jeep Wrangler TJ 2004 4.0L 6 cylinder engine. Hopefully, you can see the air intake system better this way. When I first looked at an engine, it looked like something from The Alien to me - just a bunch of hoses, tubes, wires, and black stuff all scrunched together. But if you only go one part at a time, it is less intimidating for me as an amateur novice mechanic.

The air filtering system has three major components. The first is the little trumpet looking intake nozzle. The next is the air box itself, which is, well, it's a box. And the last component is that big tube running all the way across the engine. I wonder what engineer thought it would be a good idea to put the air filter on the right side of the hood when the hose would end up connected on the left!

This design has a couple of advantages. First, the trumpet points up and the box is contained, so if you try to drive across a river, and your engine is half-submerged in water, the air intake nozzle will be above the waterline. That's a good thing, because when an engine gets water in the air intake, a condition known as hydro-lock can result.

The other advantage it has is that the air filter itself is made out of paper, and if water does go in the little trumpet, one at least can hold out hope that the air filter, soaked with water, will swell up and prevent much from getting in. Also, the swelling should choke the engine, since every engine needs gasoline and air to run.

Also, this filtration system provides excellent filtering and really clean air to the engine, as long as you change the filter at the recommended intervals in the schedule of maintenance book you got with your Jeep. And, the closed box with the raised trumpet looking intake nozzle does an OK job of getting cool air into the engine that has not been heated by passing through the radiator. So, that's why it looks like that.

Changing the Air Filter

Difficulty: Easy
Competence Required: Novice
Time Required: 5 minutes
Recommended Tools: Mechanic's Gloves
Required Parts: New Mopar Air Filter

The steps to take here are pretty simple.

In the picture below, my air filter is obviously dirty, but it could have gone another oil change before I switched it out. For me the amount of dirty you see here is my threshold for dirty. More than this - change it. Less than this, leave it.

The red arrow is pointing to the extra rubberized foam on the air filter I bought. Take it back and drive 30 miles? Heck no! I cut off the foam with a box cutter along the dotted line - careful not to tear the paper or damage it.

Now, wasn't that better than taking it to EZ-Cheezy Lube and having some high school drop out bring your filter in to show you how dirty it is, charge you $15 for a new filter (which is a cheap piece of crap that won't filter worth a hoot), and then have him put the wrong thing in your Jeep? You are well on your way to becoming a junior amateur mechanic!

Why I Used Mopar

I used a Mopar filter in my Jeep, even though for $11 I could have purchased another brand of filter at the local auto parts store (AutoZone, Advance Auto Parts, NAPA, etc). Why did I put an expensive Jeep stealership filter in my air box? The first time I ever changed my air filter, I went to the auto parts store and tried a couple of brands of air filter. I tried a Fram and I tried an STP. I bought the STP, because unlike the Fram, it didn't look like it was made out of recycle toilet paper. The STP filter did not fit snugly into the airbox. It was loose. Obviously it was not custom fit to ensure it would fit in my air box. Also, instead of the metal grill holding it together strongly, it had a line of what looked like Elmer's Glue going down it in a line to keep the pleats in order. Frankly, I think it was an inferior product to the Mopar filter available at the Jeep stealership.

So, what the heck, I dropped in a stealership filter. Every combustion engine uses three things to run: fuel, electricity (spark), and air. If the air is dirty, your engine won't last long, and it won't work very well.

Therefore, I recommend the Mopar air filter from the stealership, even though at $30 you feel like you are being held up at gunpoint. When I find out the company who produces the filter so that Jeep can rename it Mopar, then I'll look for an alternative source for them and post it here. Always avoid going to the stealership whenever possible, that's my Jeep maintenance motto. As you read other descriptions and how-tos here, you'll see why.

Air Filter Controversy

Now that you know how to change your air filter, let's discuss the pros and cons of the different methods of upgrading your air filtration system, and whether or not that's even a good idea. issue to tackle is whether or not you should upgrade your air filter. Upgrading your air filter usually involves pulling out the current air intake box, shortening the air intake hose, and putting on a high-performance, reusable, washable, air filter such as those made by K&N.

K&N produces a high performance air filter. Basically you replace the box and trumpet with a thing that looks like, uh, I don't know what it looks like. But it basically results in a huge surface area for sucking in air. According to some, this systemfilters "good enough", although I don't think anyone believes it filters as well as the stock system, and that it will allow the engine to take in more air and therefore have more horsepower.

People who buy 4 cylinder 2.4L Jeep TJ's are always asking about these filters because they think they might get a little closer to the performance of the 4.0L 6 cylinder engine if they can modify the air filter.

Others have told me that this air intake won't result in improved air consumption by the engine, because the exhaust is a bottleneck as well and must be modified to have a high-performance model of muffler or the engine won't pull enough air in to make a difference.

Fans of the stock system say the high performance filters don't improve performance with or without a new exhaust, and that people who like them are falling for a placebo effect. They like the noise they make and hear better performance even if they don't get it, they say. They also say that these filters let a dangerous amount of silica dust into the air system, increasing engine wear and decreasing engine lifetime. Lastly, they point out that you take this special filter in water, and the engine is going to hydro-lock.

Fans of the high-performance air filters say that it filters good enough, that they don't plan on soaking it in water, and that they love the improved performance, the sound it produces, and the fact that they don't have to buy filters for it. That's because these filters are washable.

So, which is it? I don't really believe it provides more power to change your air filter. Jeep Engineers have stated repeatedly that the Jeep's air filtering system is non-restrictive. That means that if you remove the filter entirely, or even the entire filtering system and just let the engine suck air directly into the throttle body, no more air gets in than with a stock air box and a stock filter. So, no mileage improvement or horsepower should even be possible with a K&N filter on a Jeep.

But, it does produce a neat, deep, throaty sound. And its kind of cool that you don't have to buy more filters. But, the system usually costs more than filters for 300,000 miles of Jeep driving, so there's definitely no cost savings. Plus, washing a filter is a bigger pain than putting in a new one. I guess I prefer the stock filtering system.

Jerry Bransford, a well known off-road enthusiast, writes that the Jeep Wrangler TJ does not have a restrictive air filtering system,

"It won't help your Jeep in the least since the TJ's OE air filter system can already provide more air than the engine can use at even WOT and high rpms. Plus a K&N is proven to let in more fine dust and silica than the factory filter does. I wish I could go back to my OE air filter system and get rid of my present K&N but I can't due to my OBA system taking up part of the space where the OE filter box sits. I had to resort to installing TWO prefilters on top of each other over the K&N to get its filtration ability back to what it was with the OE filter due to the dusty desert conditions my TJ is wheeled in.

"...the 4.0L's intake is a different beast and does indeed (!) have more airflow capability than the engine is capable of drawing at WOT and high rpms. This information comes literally and directly from the senior-most Jeep engineer known as the "father of the Jeep Rubicon" who has been there since AMC days. In a personal phone conversation I had with him (several, actually) discussing a different issue, I brought up the air intake system and he assured me it was one of the few air intakes on a production vehicle that did have greater air flow capacity than the engine can consume. He (first name is Jim) listed several Detroit vehicles that would benefit from a freer-flowing air intake system (HP Mustangs and HP Camaros to mention two) but he was convincing in his statement that the TJ was not one of them.

"From my personal experience between the stock airbox, a bare K&N, and K&N with two pre-filters over the top of it, I'm convinced he is right and that there is not one iota's worth of difference in performance between any of them. I also believe that anyone noticing a performance boost on their TJ after installing an aftermarket air intake system is a victim of the placebo effect. Plus, it's darned hard to admit (or even believe) that an expensive aftermarket air intake purchased to replace the factory intake didn't outperform it."

Let's Go Snorkeling

There's a third option that everyone agrees is a good one if you are worried about dust, getting nice, cool, clean air into your engine, increased gas mileage, and safety when crossing a river. That solution is the snorkel. I've read some pretty funny remarks from people about how guys with snorkels who don't do river crossings or drive in extremely dusty conditions are posers because they don't really need them, but other than that, I don't see a downside to having a snorkel other than the fact that you have to cut a hole into the side of your Jeep to mount it.

Reading Assignments

As if I am the first guy to ever write about Jeeps on the web and upload some bad digital photos! Here are some places to visit that will learn you straight about air filtering goodness.

Stu Olson's Air Filter Change Tutorial - Stu knows best when it comes to working on your Jeep. Read and learn, young padawan apprentice.

An Independent Study of Aftermarket Air Filters - Here's the bottom line conclusion: the OEM air filter works best, and there is no horsepower gain for a Jeep using an aftermarket high-performance air filtering system. It's just louder.

Adam Lotz' $40 Filtering Mod - Adam Lotz has a great write up on a way to only spend $40 on installing one of those controversial K&N air filters without buying the $300 kit for a Jeep. CAUTION: without the kit's air box, the filter will be sucking in hot air, and performance gains, if even possible, will probably be negated. But it sure is pretty!

K&N - The guys that make the most famous high performance filters. There are other brands out there that have different pricing, but K&N is the icon of high performance filtering. And, since I mentioned them, and then cast doubt on their product, here's a link for them.

JeepForum.com Disscussion of K&N Filters - Here's a link to a recent discussion on K&N air filters and whether or not they are helpful.

Quadratec - Quadratec has snorkels for sale. Type snorkel into the search box and hit it. They will take you to a page of snorkels.

Mark Stephens' Snorkel - This is a hilarious page. Start at the bottom - that's where he discusses snorkels and the reasons he has one on his Jeep.

A Snorkel Installation at JeepForum.com - A great set of pictures of a guy with a beautiful gold colored Rubicon that is now snorkelized. The kit came with a special box to replace the lower part of the stock air box.