On a 1996-2002 Ram 2500 or 3500 with the 5.9 Cummins, the 47RE's cooler lines are a long run of steel tube and rubber hose that ties the transmission to two coolers, and every joint in that run is a place to lose fluid or lose flow. Most people replace the lines because one is weeping or rusted through. The better reason is that the cooler circuit is also the lube circuit and the converter release circuit on this unit, so a line job is the right time to prove the whole circuit flows.
This guide covers the factory routing, the two fitting problems unique to these trucks (the 1997 connector recall and cracked cases from tapered pipe threads), the flow test you should run before and after, and how to install a replacement set so it stays dry. Specs come from Sonnax, ATRA's GEARS magazine, NHTSA, and a manufacturer's install sheet for this truck. Sources are listed at the end.
How the 47RE Cooler Circuit Is Routed
Two lines leave the passenger side of the case: a front fitting and a rear fitting. The front fitting is the feed out to the coolers. The rear fitting is the return, and that is where Sonnax and GEARS both take their measurements (more on that below). When you crack the front line loose, expect fluid to run out of the case port. Fleece Performance's install sheet for these trucks calls that out as normal.
From the case, the factory lines run forward along the driver's side of the transmission in a retaining clip, then to two coolers in series:
- The coolant-to-oil heat exchanger on the rear passenger side of the engine block. The line nuts there take a 7/8 in. wrench.
- The air-to-oil cooler mounted to the radiator assembly with three 10 mm nuts. The lines connect to it with two quick-connect fittings just behind the frame support, on the passenger side of the steering box, and you need a quick-disconnect tool to release them.
That gives you, counting both ends of every line, eight or more sealed joints plus several rubber hose sections clamped over steel. On a truck that is 25 years old, the steel sections near the frame rust from the outside, and the rubber goes hard where it sees exhaust heat. Those two failures are why most of these line sets get replaced.
The Two Fitting Problems Specific to These Trucks
The 97V084000 connector recall
Chrysler recalled about 960,000 1994-1997 Dodge Ram trucks under NHTSA campaign 97V084000 because the connector that held the cooler line to the transmission was made of a material that could melt. Per the NHTSA record, under certain high-load conditions the fluid temperature could exceed the melting point of the connector, the line would not stay connected, and fluid could spray onto the exhaust manifold, causing smoke or fire. The remedy was to replace the high-temperature side connector fittings with connectors that use a stainless steel retainer.
If you are working on a 1996 or 1997 47RE truck, look at what is in the case before you order parts. If you still see an original plastic-bodied connector on the hot side, treat it as suspect regardless of whether it is leaking, and check the VIN for open recalls. A line that pops off at highway speed under a tow load does not leak slowly; it empties the transmission onto the exhaust.
Cracked cases from tapered pipe threads
The case fittings on these units screw in with 1/4 in. tapered pipe threads, and the taper is the problem. Keep tightening a tapered fitting and it keeps wedging the aluminum outward until the boss cracks. A weep that comes from the case right around the fitting, not from the line nut, is often a crack, and a new fitting will not seal it.
Sonnax makes a repair for exactly this on the 42RE through 48RE family, its 22000-01 cooler line adapter. Per the Sonnax instructions, you remove the OE fitting, re-tap the hole with the tap from the 22000-01K kit until the tap bottoms, clean out the chips, and install the adapter. The adapter seals on its leading edge where the tap bottomed, which keeps fluid from reaching the crack. Sonnax says to pull the adapter back out once, look for a contact witness mark on the leading edge (no mark, no seal), then reinstall it with threadlocker and thread the OE fitting into it with sealant. The kit is for cases with 1/4 in. pipe fittings only, and the case can be saved without pulling the transmission.
The lesson for any line job: do not use the case fitting as the thing you crank on. Hold the case fitting with a backup wrench while you break the line nut loose (Fleece specifies a 15/16 in. backup on the case fitting), and when you install new fittings, use sealant and a torque wrench instead of feel.
Flow-Test Before You Buy Anything
A leaking line is obvious. A restricted circuit is not, and it does more damage. Sonnax's tech article on 46-47RH/RE cooler and converter flow calls cooler restriction "by far the most common issue" on this family. It lists the restriction points as the drainback fitting, the auxiliary or radiator coolers, and the lines themselves, and says the trouble can start as cooler head pressure approaches 80 psi. The symptoms Sonnax ties to low cooler and converter flow are worth memorizing, because none of them look like a cooler problem at first:
- P0740 / P1740 converter clutch codes
- TCC slip at high torque, which is exactly when a Cummins truck is towing
- Delayed engagements and slow converter fill
- Excessive stall speed
- Hydraulic noise
Here is the test, from Sonnax's instruction sheet for its 22771A-01 switch valve, which covers the 47RE:
- Disconnect the return line at the rear of the case and route it into a marked container.
- Start the engine and put it in Drive at idle, with the brakes held.
- Flow must be at least 1 quart in 20 seconds (0.8 gpm).
If you have a flow meter in the circuit, Sonnax gives the good readings as 0.7 to 0.9 gpm at idle in Drive, about 1.8 gpm at 45 mph with the TCC off, and a rapid rise to 2.1 to 2.2 gpm when the TCC applies. That last number matters: if flow stays low until lockup and then jumps, Sonnax's flow article points at restricted release oil inside the converter rather than the coolers.
When flow is low, split the circuit. GEARS magazine's 47RE case study (a 1999 Cummins that stalled at stops when warm) uses two quick checks. First, loop the lines to bypass the coolers entirely and retest; if the symptom goes away, the restriction is in the coolers or lines. Second, blow air into the rear cooler fitting at no more than 40 psi; it should pass with minimal resistance. GEARS points out that a restricted return inside the transmission acts exactly like a restricted cooler, so a clean external circuit does not clear the unit.
Flush or Replace the Coolers After a Failure
Sonnax's instructions say it plainly: if a previous converter failed, the remains end up in the radiator. The same is true of clutch material and pump debris from a failed unit. New lines bolted to a cooler full of debris will feed that debris straight back into a fresh rebuild.
- Air-to-oil cooler: it is inexpensive and difficult to clean fully once it has seen a converter failure. Most builders replace it.
- Block-mounted heat exchanger: back-flush it with a cooler flusher and blow it dry, then flow-test it on the truck after installation.
- Drainback fitting: Sonnax names it as a restriction point. If your truck has one in the circuit and flow is marginal, inspect it.
Whatever you do, the final proof is the same flow test after the install: 1 quart in 20 seconds or better at the rear return.
Replacing the Lines: Step by Step
This sequence follows the Fleece install sheet for 1994-2002 Cummins trucks with the 47RE or 47RH, adapted to apply to any replacement set. Plan on 1.5 to 2 hours.
- Park level and disconnect both batteries. The lines run close to the starter cable and the exhaust.
- Release the quick-connects at the air-to-oil cooler with the quick-disconnect tool. Drain the lines and the cooler into a clean pan so you can look at what comes out. Silver or black sludge means a cooler flush or replacement is not optional.
- Unclip the lines at the clip behind the quick-connects and the clip along the driver's side of the transmission.
- Disconnect the heat exchanger lines at the block (7/8 in.).
- Disconnect the lines at the case, holding the case fittings with a 15/16 in. backup wrench. On a 47RH, also disconnect the external transmission temperature sensor.
- Inspect the case fittings and bosses. Any crack at a boss gets the Sonnax adapter repair before anything else goes on.
- Install the new lines loosely along the factory path, keeping them clear of the exhaust and the steering box, and secure them with clamps before tightening anything.
- Torque the fittings to spec. On Fleece's kit, the new 1/4 in. NPT case adapters go in with thread sealant at 22 ft-lb, and the -8 AN line fittings get 270 to 350 in-lb, always with a backup wrench on the case adapter. Follow your kit's numbers. Aluminum AN fittings damage easily when overtightened.
- Refill with ATF+4, run the engine, and recheck the level hot in Neutral. Then run the flow test at the rear return line.
- Check every joint for leaks after a heat cycle and again after the first drive with some load on it.
Upgrade or Stock?
Aftermarket braided or hose kits with -8 AN ends (1/2 in. ID) are the common upgrade on these trucks. They remove the rusting steel sections and the rubber hose splices, which are the two main failure points. The trade-off is more fittings, and AN fittings on aluminum need correct torque and a backup wrench. Some kits also delete the block-mounted heat exchanger and run only the air-to-oil cooler. That cools better when the truck is moving and worse in slow, hot, loaded crawling, so think about how the truck is used before you delete it.
If the truck tows heavy, a deep finned pan adds fluid capacity and surface area, and a temperature gauge tells you whether the cooler upgrade worked. Our 47RE overheating guide covers temperatures and the full cooling picture.
RE-Family Filter and Gasket Kit, 1998-2009
If the flow test or the drained fluid shows debris, the filter comes out with the pan. This kit fits the 1998-2002 47RE as well as the 48RE. Confirm your year before ordering.
See the filter kit →Shop RE-family transmission parts →
Frequently Asked Questions
Which 47RE cooler line is the return line?
The return line is the one at the rear fitting on the case. Sonnax measures cooler flow at the return line at the rear of the case, and GEARS magazine uses the rear cooler fitting for its air check of the internal return path. The front fitting is the feed out to the coolers, and it will dump fluid when you crack it loose.
How much fluid should flow through a 47RE cooler?
Sonnax's spec for the RE family is at least 1 quart in 20 seconds (about 0.8 gpm) from the return line, in Drive at idle. With a flow meter, good readings are 0.7 to 0.9 gpm at idle in Drive, about 1.8 gpm at 45 mph with the converter clutch off, and a quick rise to 2.1 to 2.2 gpm when the clutch applies.
Were the 47RE cooler line fittings recalled?
Yes, on the early trucks. NHTSA campaign 97V084000 covers 1994-1997 Dodge Ram trucks, about 960,000 vehicles, because the connector holding the cooler line to the transmission could melt under high-load fluid temperatures and let the line spray fluid on the exhaust manifold. Dealers replaced the high-temperature-side connector with one that has a stainless steel retainer.
Do I need to flush the cooler when I replace the 47RE lines?
If the transmission or converter has failed, yes, or replace the cooler. Sonnax notes that when a converter fails, its debris ends up in the radiator cooler, and cooler restriction is the most common flow problem it sees on 46/47RE units. New lines on a plugged cooler only move the restriction somewhere else.
Sources
- Sonnax — "46-47RH/RE Cooler and Converter Flow" (Bob Warnke). Backs cooler restriction as the most common issue in this family, the drainback fitting, coolers and lines as restriction points, trouble as head pressure approaches 80 psi, the symptom list (740/1740 codes, TCC slip at high torque, delayed engagement, slow converter fill, excessive stall, hydraulic noise), and low flow until TCC apply pointing at the converter. sonnax.com
- Sonnax — 4-Spool Switch Valve 22771A-01 instructions (42RE through 48RE), section 7 "Critical Pump & Cooler Flow Quality Adjustments." Backs the minimum flow of 1 quart in 20 seconds (0.8 gpm) at the rear return line in Drive at idle, the 0.7-0.9 / 1.8 / 2.1-2.2 gpm flow readings, and converter failure debris ending up in the radiator. Sonnax instructions (PDF)
- Sonnax — Cooler Line Adapter 22000-01 instructions. Backs the cracked-case repair for 42RE through 48RE cases with 1/4 in. pipe fittings: re-tap until the tap bottoms, leading-edge seal and witness mark, threadlocker on the adapter and sealant on the OE fitting. Sonnax instructions (PDF)
- NHTSA — Recall campaign 97V084000 (Chrysler, 1994-1997 Dodge Ram). Backs the connector melting under high-load fluid temperature, line separation and fluid spraying on the exhaust manifold, about 960,000 affected vehicles, and the stainless steel retainer remedy. NHTSA recall record
- ATRA GEARS Magazine — Mike Brown, "A Dead Stop! A Typical Dodge 47RE Problem With an Unexpected Solution." Backs looping the lines to bypass the cooler, the no-more-than-40 psi air check at the rear cooler fitting, and a restricted internal return acting like a restricted cooler. gearsmagazine.com
- Fleece Performance Engineering — Install sheet FPE-2024-115, cooler and line kit for 1994-2002 Dodge Ram 2500/3500 Cummins 47RE/47RH. Backs the factory routing (heat exchanger on the rear passenger side of the block, air-to-oil cooler on the radiator with quick-connects behind the frame support), wrench sizes, fluid from the front port, install time, and the 22 ft-lb NPT adapter and 270-350 in-lb AN torque figures for that kit. Install sheet (PDF)
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