NWMP 32-Gallon Replacement Gas Tank in a Cherokee XJ
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By: Berkeley Johnston - 12/2004

NWMP 32-Gallon Replacement Gas Tank in a Cherokee XJ

Extra Capacity Wanted

Fuel capacity, and lots of it, that's what we like. A trademark accessory for the Jeep has always been a red 5 gallon fuel can. I think it represents the conservative nature of Jeepers: thinking ahead, playing it safe, and willing to help others. They're also popular because those old tanks were so darned small. In any case, I don't have the room for a Jerry can on my Cherokee. The original tank on my Cherokee isn't particularly small, either, but trips like the 32 mile Dusy-Ershim trail would drain it. Wanting to carry five or ten extra gallons of gas was important, but what to do?



Tank and Fuel Pump Damage

Meanwhile, I began to really abuse my Jeep. I didn't notice the damage at first, but my tank started slowly shrinking... caving in, actually. The Wrangler (the YJ, anyway) has a nice setup, with a steel skid plate and a plastic tank. It's easy to remove the skid and bang it back into shape. The plastic tank just pops back to normal. Been there, done that. The Cherokee, however, has an opposite arrangement. Instead of a metal skid plate with a plastic tank, mine was a plastic-covered metal tank. So, the Jeep slams down on a rock, caves in the tank, and the plastic cover happily pops back into shape hiding any dents! Again... been there, done that. The short story is that, after four years of banging around on the rocks, my tank had shrunk from a theoretical 20 gallons to much less. The worst of it, however, was the invisible damage. The fuel pump and sender unit was bent up into the tank, dropping my practical capacity down to the low teens. The fuel pickup was bent up into the tank and wasn't able to suck the last five or so gallons. No wonder I could never get my gauge to read above half!

The plastic shroud (left) protects against scraping action, but hides impact damage to the metal tank. Once off (right), the severe damage is obvious. The center image shows the underside of the XJ without the gas tank.

NWMP Tank from RRO

Replace the stock tank and add a metal skid? Or bite the bullet and get the big tank? I decided to kill two birds with one stone. Make that three birds, if you include my wallet! These tanks are seem a little expensive, but more on that later. I found two companies that make large capacity replacement tanks for the XJ, Northwest Metal Products and Aero Tanks. A couple XJ guys I know had installed the NWMP tank and liked it. They had only good things to say. Plus, Rocky Road Outfitters, from whom I've always received excellent help, sells the NWMP product. Getting to deal with RRO again made the decision easy. The NWMP tank comes complete with everything, so when it's all said and done, the large price tag isn't as bad as it seems. The original fuel pump is reused, and the existing filler hoses are cut down and reinstalled. One vapor recovery valve is also transferred to the new tank. Other than that, it's all there: tank, sender, hoses, clamps, screws, wire, nuts, bolts, washers, instructions... everything. Hmmm... maybe this tank isn't as expensive as it first seemed.

More tank damage is visible in the left image. The center and right images highlight the hidden damage to the in-tank fuel pump. The hard return tube is kinked, and the once-perpendicular mounting plate is cocked at an angle. Closer inspection of this plate shows broken welds and fresh metal.

Removal of the Old Tank

I tried to drain as much gas out of the tank as I could by driving until it was near empty. Removing the old tank was straight forward. Like I usually do when working under it, I had the Jeep elevated on ramps and large blocks of wood and properly immobilized. I like being able to sit under the Jeep while pondering current and future projects.

There are three small rubber lines to remove, an electrical connection, and two large fill hoses. The electrical connection and small hoses are easy to access from the front edge of the tank. There's still gas in the feed line, so be ready to catch the extra gas. To keep them clean during the project, I plugged the loose lines with assorted-sized vacuum plugs fitted loosely. The larger hoses are accessible under a removable dirt shield on the driver's side. Once all these hoses are free, the tank can be dropped. It's amazing how much gas weighs if you're lying on your back. If the tank isn't empty, siphon the remaining gas before trying to drop it.

Preparation of the NWMP Tank

Instructions seem to be written by people who know everything about the project, but invariably forget that the people reading them don't. Nevertheless, the instructions are adequate, and I had no problem assembling the tank.

The original Cherokee has a combination pump and sender, but the NWMP tank separates these. A new sender is included and is easily installed after a quick check for proper orientation. The fuel pump and pickup tube/screen are reused, and are integrated into a new bracket. One question left to the user is the alignment of the feed and return lines on the pump assembly. Before screwing down the pump plate, make sure the hoses can be attached without getting caught or kinking during installation. One suggestion for improvement to NWMP would be to flare the feed and return lines. They're slippery and I found myself wanting to over tightening the clamps. In the end, I used two clamps per line to keep the connection strong and sealed.

The old bracket lies next to the new fuel pump assembly (left). Detailed instructions made this step easy. The center image shows the vapor recovery valve, sender, and fuel pump plate installed and ready for fuel lines. Electrical connection: black is ground, purple is sender, and orange is pump.

Transfer one of the two original vapor recovery valves to the new tank. I didn't want to risk breaking or cracking the plastic valves, so I soaked them with silicone spray to help with removal and reinstallation. The instructions say to reuse some of the original hose to connect this valve, but the new hose included in my kit was adequate.

The instructions fall short explaining how to prepare the large rubber fill hoses. I used a combination of strategies here. I read the instructions about a dozen times, and alternated the reading with a heavy dose of common sense and a lot of test fitting of the metal fill tube and hoses. Ah... another tip here. I removed the metal fill tube from behind the gas door, and found that to be very helpful. Sorry, too wordy. Here it is: the hoses need to be cut a little shorter. Because the hoses are pre-formed into bends, it's a little tricky. Rather than cut X amount off of one end, I cut a little from both ends. Not too hard... you'll get it.

Installation of the New Tank

NWMP provides a new set of straps for the tank, and a new way to attach the straps to the rear of the vehicle. It's a pretty straightforward job, but I've got a knack of making simple things difficult. The new straps are supposed to be attached using a set of supplied bolts. The bolts hang from a couple of holes you drill in the body directly below the existing strap-attach slots. The provided bolts didn't seem quite long enough, though. I think my trailer hitch might have been getting in the way. Or something. Anyway, I ended up reusing part of the original straps to attach the rear of the tank. I cut the factory straps down in length and bent the ends to match the new straps. I used the provided bolts and nuts to join together old and new. Pretty slick, actually.

The instructions explain where to drill new holes for the bolts (center image) and how to hang the new straps (right). Either the bolts weren't quite long enough, or my hitch interfered with the new straps. Ultimately, I modified the original straps, strong and secure, to hang the tank.

Tricks, Tips and Modifications

I've already gone over a few tips in the above text. One thing yet to accomplish is to add a skid plate. The new tank is quite stout, but could still be damaged on the rocks. An easy way to protect the tank is to insert a skid plate between the tank and the straps, material somewhere between 1/8" to 1/4" thick. I think quarter inch is too thick, but I'm not that rough on my Jeep. And maybe add a thin rubber sheet between the tank and the skid. And maybe stitch-weld the straps to the skid plate. And maybe use stainless steel to help it slide over the rocks more easily. And... that's a lot of sentences starting with And.

The new tank hangs from the front by the original special bolts. The tank is huge and takes advantage of nearly all available space in its location. It hangs down further, too, which might be a problem. A custom-sized tank, with a few less gallons, might be the answer for more clearance.

Results

My initial filling was about three gallons of fuel siphoned from the dirt bikes. The Jeep started right up. The low-fuel warning light was on, but I didn't have any problems going up or down hills. I drove about five miles to the gas station, where the tank took 30 gallons! That means I've got at least 30 usable gallons on-board. Unlike factory tank sizes seem to be, this tank is advertised with a true capacity of 32 gallons. With the new tank, I can carry the equivalent of three 5-gallon cans of extra gas. Wow! I don't have a red Jerry can hanging off the back of my Jeep, but as long as you've got a siphon hose, I'm happy to share.

The dash gauge reads true, which is great. Surprising, but great. It reads Full after a fill, and drops steadily toward Empty until the little warning light comes on. The gauge definitely hunts up and down on the hills. There are baffles in the tank to prevent sloshing, but the gas is free to slowly shift around. It's not a big deal, and adding blocks of fuel cell safety foam would minimize this. (Summit Racing, SUM-290190.) I'm going to skip the foam idea. Near empty, the shifting gas makes the warning light blink on and off for a while. No problem, though. Once the warning light comes on steadily, there are four or five gallons remaining.

Is this project worth the price of money, time, and trouble? Yes. In spite of the initial sticker shock, installing this tank was a good idea. You get what you pay for, I always say. Now that I think about it, I bought a pair of cargo shorts a couple months back at Wal-Mart. American Eagle I think they're called, and they sure are nice. They've got a nifty place for my cell phone and everything. Cheap, too! So, I guess sometimes you get a little more than you pay for. The NWMP 32-gallon replacement gas tank isn't exactly a pair of shorts, but I'd buy them both again. No joke.


Northwest Metal Products 32 gallon replacement gas tank, part AMC-2. Purchased from Rocky Road Outfitters (tank listed on the engine products page).


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