How To Drive A Jeep Underwater

I was wearing a special scuba mask that allowed me to talk to and hear other people underwater as I let out the clutch and rolled into the pond. The tires stayed planted, and I plowed ahead as my vision went black. It wasn’t actually black. It was more like a tan, the color of coffee with a half-dozen creamers dumped in. The Cummins was still running, and that was a good sign. Then the dust started to clear, and I thought I was starting to climb the opposite side of the pond. I couldn’t believe it! I was crossing this old pond! And then it got dark again. The whole time, I was in second gear low, and the engine was locked at about a quarter throttle. I didn’t know how much more or less it needed, and I had no idea if I was moving or not. Then I remembered my microphone and called out to the other scuba guys and my friend Rob in a canoe above me.

“Hello? Hello? Anyone out there?” Nothing.

Jeeps are designed to conquer almost any terrain, but driving underwater isn’t really what they were made for. It’s true that if you search “underwater jeep” on YouTube, you’ll find a 1952 newsreel video showing a white M38 military jeep driving underwater with a tall snorkel, but it’s been a while since Jeep designed in “fording” as part of its repertoire. I was game to return to this original programming as part of the 75th birthday celebration of the Jeep brand and to do it with my 1997 Jeep Wrangler affectionately known as Tube Sock.

Tube Sock is a white Wrangler I bought with a little 2.5L gas engine and transformed for a trip to the Moab Easter Jeep Safari back in 2014. It has Currie axles, (44 front, 60 rear) and clears 37-inch tires. The plan was to build it low and stable but also strong so I could drive it like an idiot. The axles have ARB Air Lockers for traction, and the Jeep uses a BDS long-arm suspension and very short coils and Fox shocks mixed with ample fender trimming for optimal tire clearance and a low center of gravity. Eventually we even shipped it to Hawaii for a second episode of Dirt Every Day in 2015. Since it survived Hawaii, it seemed like the next logical step was to drive it underwater.

dirt-everyday-underwater-jeep-009 In the early 1950s the military tested REO trucks and jeeps for deep-water fording, but oddly enough, no one does it anymore.

Driving underwater was an idea hatched by Angus MacKenzie back when we started Dirt Every Day. He sent me an old photo of a military truck underwater and said, “Do this.” I agreed it would be epic, but the submarining of a 4×4 sunk to the bottom of the to-do list until early this year when I was talking with a friend at Cummins (the diesel engine company) about their prospective crate-engine program. Cummins had helped me last year with a V-8 diesel in my Mad Maxxis Off-RoadRunner build and wanted to do something new with their smaller I-4 diesel engine. Then it all came together fast.

Cummins wanted to put a small diesel in a Jeep on Dirt Every Day. I wanted to drive underwater. I had a Jeep that needed a new engine. Diesels are usually pretty well sealed for rough terrain, and underwater is pretty rough terrain. When the Maxxis tires guys also wanted in on the idea, I knew we had all the hard parts, so I approached Advance Adapters, who has been making a living helping Jeep owners swap in engines for years, and they were thrilled at the prospect of a small crate diesel engine swap. Underwater Jeeping floated to the top of the to-do list.

dirt-everyday-underwater-jeep-006This is not the Cummins 4BT. It is a smaller, lighter engine that’s better suited for a Jeep. I can’t wait for stage two when we remove the Jeep’s scuba gear and make it a long-range trail machine.

The new Cummins ISF2.8 is 540 pounds versus the Jeep’s original gas four-cylinder’s 350, but it has 266 lb-ft of torque and 160 hp up on the gas’ 140 lb-ft/120 hp. And that’s in stock form; I know those numbers can go up with aftermarket support. So even though we only gained 0.3 liter, we added a fair bit of power even if it is a little heavier.

I tore the old engine, transmission, and transfer case out and headed to Advance Adapters. Cummins arrived with the new engine, and AA convinced me to go with a stronger NV-3500 five-speed manual and their venerable Atlas transfer case. This meant no electronic transmission gremlins to fight, and I knew the drivetrain past the engine would be fine even if filled with water; an automatic might not be so willing to chug H2O.


The ISF2.8 is a common-rail diesel and is computer-controlled, which meant more challenges to make it waterproof, but we had plenty of smart guys working on the project—and one dummy. The goal was to keep water out of the intake, exhaust, fuel, and computer. The crankcase was a mystery. Do we pressurize it so water doesn’t sneak past the oil seals? Do we just vent it above water line? Or should we seal the vents and let the internal pressure self-regulate? We opted to vent it and cross our fingers.

We added new motor mounts but didn’t install a fan so it wouldn’t smash into the radiator when whipping through the water. We used a 4.0L I-6 radiator, but we held off on an intercooler until after the dive test, electing to use a crossover pipe from the turbo to inlet. The Air Lockers ran off a Powertank CO2 tank instead of an electric air compressor and used pneumatic switches. The gearboxes and axles had their vents capped; we wouldn’t see enough driving to get them warm prior to the swim.


The rollcage and nice seats were removed and replaced with a pair of basic low-back seats from Bestop. For obvious reasons, I wanted quick and easy exit from the Jeep if it stopped running, and the low backs would allow whatever scuba gear I needed to be accessible.

The wiring waterproofing was a mixture of dielectric grease on every terminal and plug, stuffing the ECU in an ammo can upside down to form a bubble, and plenty of goop to seal around the wires entering the can. We used expanding foam and pliable undercoating to try to make a good seal then greased the old military gasket on the ammo can and hoped the trapped air bubble would keep it dry.

We finished it with a pair of 16-foot-tall snorkels, one for the intake, one for the exhaust, and a pair of vent hoses, one from the fuel tank (a converted portable air tank with a sealed pipe-fitting filler neck) and one for the crankcase. The snorkels had to be removable, so we sealed them with black silicone (intake) and high-temp silicone (exhaust) and clamped the pipes down hard with exhaust clamps. Both snorkels had cables running to the front and back of the Jeep so they wouldn’t flop around or bend in the water.


We headed to a pond on private property because driving right into a public lake might raise some eyebrows or disrupt some local snail ecology or something. Before I drove in, we decided that adding water to the back two 37-inch Maxxis Trepador tires might be a good idea. I didn’t think the fronts would float with a Cummins above them, but the rears might just have enough buoyancy to keep it off the bottom. Again, we didn’t know for sure, and adding traction didn’t seem like a bad option.

We also dragged a giant rake across the pond to try to clear out the swamp grass growing on the bottom. It didn’t work.

Then, after many weeks of work and months of planning and a few days of scuba training, I took the plunge with Tube Sock.


The Dive

I hadn’t thought through the visibility issue of the muddy pond. I was underwater and in the dark and trying not to panic from the radio silence. “Hmmm, I wonder if I’m moving or not? I wonder if I’m driving in circles.” The Jeep power steering had been replaced with a manual box, but I still wasn’t sure what was going on. The disorientation of zero visibility was overwhelming. I love a daily cup of coffee with cream, but never had I thought I would be sitting in a cup of the stuff. Plus, this coffee was chilled, and so was I. It was all getting really weird.

Then a hand touched my shoulder, and I could hear someone. It turned out the radio system would only work when the other diver was right beside me.

“Yes, I’m OK.”

“Am I almost across the pond?” (Nope.)

“Am I moving?” (Sorta.)

“Am I stuck?” (Probably.)

“OK, I’m going to try reverse. Look out.”

I shifted into reverse and let her eat going backward. Then the coffee went from tan to black. As the tires spun and threw up even more silt, I couldn’t even see the sunlight from above. It was just black. But I could feel the Jeep move backward, or rather the water rush forward. I moved back a little and then started forward again, but I fell right back in the holes I had dug prior. At this point I had no idea what was going on. I couldn’t see my tires, the windshield kept me from knowing if the Jeep was moving forward, and some mixture of swamp grass and pond muck was holding me still. I was getting cold, and I couldn’t communicate with anyone but a single diver.

But the Cummins kept singing.

At this point I forgot the rules of four-wheeling—back up and take another line, try a different gear, throttle down! I was trying to keep it slow and steady, and all I was getting was stuck and muddy. When the camera guy finally told me progress was stopped again, I opted for the hook, and my good old Cummins-powered tow rig dragged my new little Cummins-powered Jeep from the drink.


Aftermath –bath I was pretty bummed. Even though we had built a diesel Jeep in two weeks and drove it underwater, we didn’t make it across the pond. It was a sink, not a swim. Rob informed me I had been under for almost an hour (49 minutes!). We had built a vehicle that would run underwater, but we hadn’t successfully driven it underwater yet.

I took Tube Sock home to wring it out and drain all the fluids, and the camera crew went back to the city to see what we got. I found the axles and Atlas water-free, but the engine oil and transmission were a bit milkshakey. (When water mixes with oil it turns to a creamy tan like a chocolate shake.) I drained and changed the oil and let the engine get warm and cool down a few times before deciding it was good to go. Then the axles and gearboxes got fresh Amsoil, and Tube Sock was back in action. About that time the call came in. “We didn’t get the shot. We want to redo the dive. We’ll find a clearer pond.”


Second Rinse The new location was a horse farm where thoroughbreds roam and couples come to get married among the rolling lawns, rocky hills, and concrete-bottomed pond. If you were getting hitched there on one particular day, you would have seen a knucklehead and his camera crew driving a Jeep into one of the clear, green ponds.

Rob was back in the canoe, I was back in my scuba gear, and Tube Sock wouldn’t start. The only electrical issue from the first dunking was a basic starter solenoid that wasn’t kicking over the starter. I swapped that, and the little torque monster came alive. It was time to dive.

This run went like clockwork (or one of those neat diving watches). I dove it, the hood came open (I forgot to latch it down, a common goober move), a scuba person latched it shut, I drove across the pond, and victory was ours. It did so well that it was over in minutes, so we did it again and got more photos. The water was warm, and the shots turned out great.

And that is how I drove a jeep underwater.

Roadkill Fall 2016 Cover