If you're staring at a puddle of red fluid under your truck, you're probably hunting for a 46re transmission cooler lines diagram to figure out exactly which hose goes where. These transmissions, which were the workhorses for Dodge Rams, Dakotas, and Jeep Grand Cherokees for years, are pretty reliable until the cooling system starts to act up. Dealing with transmission lines isn't exactly a fun Saturday afternoon, but getting the routing right is the difference between a happy gearbox and a very expensive paperweight.
Let's break down how these lines actually work, where they go, and why the factory setup sometimes leaves a bit to be desired.
Identifying the Ports on the Transmission
Before you even look at the radiator or the auxiliary cooler, you have to know which port is doing what on the 46RE case itself. If you're lying on your back looking up at the transmission, you'll see two threaded ports on the passenger side.
The front port, which is the one closer to the engine and the bellhousing, is the "out" or pressure port. This is where the hot fluid leaves the transmission to go get cooled off. The rear port, located further back toward the tailshaft, is the "return" port. This is where the cooled fluid comes back into the transmission to lubricate the internals and keep things from melting down.
It's easy to mix these up if you aren't looking at a diagram, but it's crucial to get them right. If you swap them, you're essentially trying to push fluid against the internal flow design, which can cause pressure issues and heat spikes.
The Standard Flow Path
Most of these vehicles come with a two-stage cooling setup. If you follow a 46re transmission cooler lines diagram for a stock Dodge Ram, the path usually looks like this:
- From the Transmission: Hot fluid exits the front port.
- To the Radiator: The line runs forward and enters the bottom fitting of the radiator's internal cooler.
- Through the Radiator: The fluid flows up through the radiator (where the engine coolant helps pull off the initial blast of heat).
- To the Auxiliary Cooler: The fluid exits the top of the radiator and travels to the external "fin and plate" cooler mounted in front of the radiator.
- Back to the Transmission: Finally, the fluid leaves the auxiliary cooler and heads all the way back to the rear port on the transmission.
This "serial" cooling method is standard because it helps warm the fluid up in the winter (via the radiator) and keep it extra cool in the summer (via the auxiliary cooler). However, if you've added an aftermarket cooler, you might be tempted to bypass the radiator entirely. Unless you live in a place that's 100 degrees year-round, most experts suggest keeping the radiator in the loop to help regulate temperatures.
That Pesky Check Valve Problem
If you're looking at your lines and you see a weird, slightly bulged section in the rubber hose part of the pressure line, you've found the infamous check valve. This little guy was designed to keep fluid from draining out of the torque converter when the truck sits for a few days. The idea was to prevent "drain back," which causes a delay when you shift into gear on a cold morning.
The problem? These check valves are notorious for clogging. Over time, tiny bits of friction material from the transmission clutches can get stuck in the valve. When it clogs, it cuts off the flow of fluid to the coolers. Your transmission will overheat in minutes, and you might not even know it until it's too late.
When people look up a 46re transmission cooler lines diagram, they're often doing it because they want to delete this valve. Many owners choose to cut that section out and replace it with a high-quality transmission-rated hose and clamps, or they buy an aftermarket line that doesn't have the valve. If you do this, just remember that you might need to wait a few seconds in Neutral or Drive for the fluid to circulate before you take off in the morning.
Common Leak Points to Watch For
The 46RE lines aren't exactly known for staying bone-dry forever. There are a few places where they almost always fail:
- The Quick-Connect Fittings: Dodge used these "snap-in" style connectors at the radiator. They're convenient at the factory, but after fifteen years of heat cycles, the internal O-rings get brittle. They'll start as a "sweat" and turn into a drip.
- The Rubber-to-Metal Crimps: Most factory lines are a mix of steel tubing and rubber hose. Where the metal is crimped onto the rubber is a major fail point. You can't really "tighten" these; once they leak, the line is toast.
- Rust on the Hard Lines: Because these lines run along the bottom of the engine and past the oil pan, they get blasted by road salt and moisture. It's common for the steel sections to rust through, especially where they are held by mounting clips that trap moisture.
Replacing the Lines: What Are Your Options?
If your lines are shot, you have a few ways to go about fixing them. You can buy pre-bent factory replacements, but honestly, those can be a nightmare to install. Trying to snake a long, rigid steel line over the crossmember and around the exhaust without bending it out of shape is enough to make anyone lose their cool.
A lot of guys opt for braided stainless steel lines or high-pressure hydraulic hoses. Using -6AN fittings and braided lines makes the job much easier. You can route the flexible hose exactly where you want it, zip-tie it away from hot exhaust manifolds, and you don't have to worry about rust ever again. Plus, AN fittings are way more secure than the factory quick-connects or old-school hose clamps.
If you go the DIY route with rubber hoses, just make sure you use hose specifically rated for transmission fluid. Fuel line or heater hose will soften and burst under the heat and pressure of a 46RE. Look for "SAE J1527" or similar ratings on the side of the hose.
Tips for a Clean Installation
When you're following your 46re transmission cooler lines diagram and putting things back together, keep a few things in mind to save yourself a headache later:
- Use Flare Nut Wrenches: The fittings on the transmission case are soft. If you use a regular open-ended wrench, there's a good chance you'll round off the nut. A flare nut wrench (or line wrench) grips all sides and is worth its weight in gold here.
- Clearance is King: Make sure the lines aren't rubbing against the frame, the engine block, or the steering shaft. Vibration will eventually rub a hole through even the toughest steel line.
- Don't Over-tighten: The transmission case is made of aluminum. If you ham-fist the fittings into the case, you can crack the housing, and then you're looking at a much bigger problem than a simple leak.
- Flush the Coolers: If you're replacing lines because your old transmission died, you must flush the radiator and auxiliary cooler. There's probably metal debris hiding in there just waiting to ruin your new build.
Wrapping It Up
Understanding the 46re transmission cooler lines diagram isn't just about knowing where the hoses go; it's about understanding how your transmission breathes and stays cool. Whether you're doing a stock restoration or upgrading to a heavy-duty cooling setup for towing, getting the flow right is step number one.
Keep an eye on those old crimp joints, think about ditching that check valve if you haven't already, and always double-check your "in" and "out" ports. It's a messy job, and you'll probably end up with some ATF in your hair, but once those lines are solid, you can drive with a lot more peace of mind.