47RE Overheating - Causes and Fixes

47RE Overheating - Causes and Fixes

47RE Overheating - Causes and Fixes

A 47RE that runs hot does not give you much warning before it starts slipping. The transmission behind a 1994-2002 Cummins was rated for roughly 450 lb-ft of input torque, it lives in a truck that tows, and it depends on a converter clutch that locks to keep heat down. When any of those three things goes wrong the fluid temperature climbs, and the numbers are unforgiving. Gears Magazine puts the ideal maximum at 200 degrees F and notes that for every 20 degrees above that, expected transmission life is cut in half. At 240 degrees the unit is living a quarter of its normal life. This article covers where 47RE heat comes from, how to find the cause, and what parts fix it.

Parts for your 47RE

47RE Master Rebuild Kit - Frictions & Steels, Gaskets & Seals, Filter, Shift Kit, Servo, Solenoids, Bushings (7-Piece) — $346.99

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First, get a real temperature reading

The 47RE trucks do not have a factory transmission temperature display, so most owners find out about overheating from a smell, a slip, or a gauge somebody added. If you do not have a temperature gauge, install one with the sender in the hot line or the pan before you start diagnosing. You need to know whether the truck is at 210 degrees in traffic (normal for a diesel in summer) or 260 degrees on the highway (a problem). Transmission Digest's towing guidance is that anything in the 200 degree range is getting critical, and that anytime the torque converter clutch is open it is generating heat.

Causes of 47RE overheating

1. No lockup (the most common cause)

An unlocked converter at highway speed is a heat generator. On the 47RE, no-lockup is usually not a converter failure; it is an overdrive/TCC solenoid, a wiring or relay problem, or a valve body pressure loss. Cummins Forum owners who chase overheating routinely find the no-lockup condition is the cause of the heat, not the result of it, and that bad or cheap OD solenoids are a frequent culprit. Transmission Digest adds a wiring detail that catches people: the 46RE/47RE transmission control relay coil is powered from the PCM's generator source circuit, which is only energized when the engine is running. If you test for solenoid power with the key on and the engine off, you will see nothing and chase a ghost.

2. Worn lockup boost valve

Sonnax identifies the lockup boost valve in Chrysler 42-46-47-48RH/RE units as a valve that is prone to wear, and states that when it wears it causes a loss of converter and lubrication flow that results in TCC slip and an overheated converter. Their symptom list for the worn valve includes overheated converter, TCC slip under load, loss of lube oil, no lockup and TCC cycling. The mechanism is that bore wear reduces oil pressure to the switch valve, which then sits in a partial stroke position that restricts the converter and lube circuits. So the converter is not being fed enough oil to cool it, and the clutch is slipping at the same time. The correction is an oversized lockup boost valve kit (Sonnax 22771-19K).

3. Low cooler flow

Gears Magazine's overheating checklist for the 48RE family lists plugged cooler lines (kinks, pinches and road damage), a plugged transmission cooler, and restricted filters as the top three causes, and specifies a minimum acceptable cooler flow of at least one gallon per minute. Monster Transmission's 47RE/48RE guide says the same: poor cooler flow or a plugged heat exchanger causes burnt fluid, the fix is to hot back-flush the cooler or replace it, and to verify at least 1.0 GPM at idle from the outlet line before the transmission goes back in. A previous failure that sent clutch debris into the cooler is the most common reason a fresh rebuild overheats.

4. Converter drain-back and a cracked drain-back valve

The 47RE has a converter drain-back valve that can crack, causing loss of converter pressure and overheating. The symptom that goes with it is a delayed forward or reverse engagement after sitting overnight, because the converter has drained down. Sonnax lists converter drain back and converter bushing failure among the 47RE/48RE symptoms its Sure Cure kit addresses, and TransGo's kit for the 48RE sibling includes a manual valve designed to reduce drain-back complaints.

5. Overload and driving style

Gears lists vehicle overload beyond the manufacturer's tow rating, engine overheating (which compromises a radiator-mounted cooler), and a fan clutch that runs below spec as overheating causes on the 48RE family, and all three apply to the 47RE. Long grades with the OD on and the converter unlocked, or lugging a heavy trailer in 4th, will push the unit past 200 degrees with nothing mechanically wrong. Transmission Digest's advice for towing customers is to keep the load 20 percent under the rating, and to select a gear where the converter clutch stays applied.

6. Wrong fluid or neglected service

The 47RE takes ATF+4, and the recommended service is fluid, filter and band adjustment every 24,000 miles or 24 months according to Diesel Hub. Neglecting band adjustment accelerates wear, and worn bands slip, and slip makes heat. Monster's guide specifies ATF+4 only and calls a first service with band re-adjustment at 3 months or 5,000 miles after a rebuild.

Diagnosis steps

  1. Confirm lockup. At 50 mph in OD, watch the tachometer and lightly tap the brake. RPM should rise about 200-300 when the converter unlocks and drop when it relocks. If RPM never changes, there is no lockup and you have found your heat source.
  2. Test the OD/TCC solenoid and relay with the engine running. Check for power at the solenoid connector and for the relay clicking. Replace the solenoid with a quality unit if it is out of spec.
  3. Check cooler flow. Disconnect the return line at the transmission, run it into a container, start the engine in neutral and time the flow. Less than one gallon per minute means a restricted cooler or line.
  4. Check line pressure and TV cable. A 47RE that will not build line rise with throttle is slipping its clutches and its converter clutch under load.
  5. Pull the pan. Burnt fluid and friction material means the heat has already done damage and the unit needs more than a solenoid.

The fixes

No lockup: replace the OD/TCC solenoid and, on 2000-up trucks, the governor pressure solenoid and sensor that share the same harness. The 47RE Shift Solenoid Kit 2000-Up with Sensor is a direct-fit replacement for the 2000-up units; more choices are in the solenoids collection.

47RE Shift Solenoid Kit 2000-Up with Sensor
47RE Shift Solenoid Kit 2000-Up with Sensor - restores lockup on 2000-up 47RE units so the converter stops making heat at cruise.

Valve body pressure loss: a 47RE shift kit raises line pressure and recalibrates the valve body; if the lockup boost valve bore is worn, add the Sonnax oversized boost valve kit, and on a high-mileage valve body a full Sure Cure kit restores the lube-regulated pressure regulator, the 4-spool switch valve and the boost valve spring retainer in one pass.

Low cooler flow: hot back-flush the cooler and lines, verify one gallon per minute, and replace the cooler if it will not flow. Adding an auxiliary cooler helps a truck that tows, but it does not fix a plugged one.

Burnt fluid and slipping: the heat has already cooked the clutches. The 47RE Master Transmission Rebuild Kit 1998-2002 with Filter covers frictions, steels, seals and filter, and the rebuild kits collection has options for other years and heavier-duty friction material.

Replace while you are in there

  • OD/TCC solenoid and governor pressure solenoid and sensor
  • Boost valve spring retainer (the OE part cracks and drops the boost valve out of position)
  • Filter and pan gasket, full ATF+4 fill
  • Both band adjustments
  • Cooler flush, and a flow check before reinstall
  • Converter drain-back valve if engagement is delayed after sitting
  • A temperature gauge if the truck does not have one

Cost and effort

The cheap end of this is a solenoid and a fluid service, both pan-off jobs that most owners can do in a driveway in an afternoon, and that is where the majority of 47RE overheating cases end. A shift kit is a valve-body-out job on the same day. A cooler flush needs a flush machine or a replacement cooler. The expensive end is a rebuild after the heat has already burned the clutches, which is why a temperature gauge and a quick lockup check are worth doing before the smell shows up. For more on this family, see the 46RE and 47RE complete guide and 47RE vs 48RE.

Frequently Asked Questions

What temperature is too hot for a 47RE?

Keep it at or below 200 degrees F under sustained load. Above that, transmission life drops by half for every 20 degrees, so 240 degrees is a quarter of the normal life. Short spikes in traffic are survivable; sustained highway temperatures above 220 are not.

Why does my 47RE overheat only on the highway?

Almost always because the converter is not locking. An unlocked converter slips continuously at cruise and makes heat. Check the OD/TCC solenoid, the relay circuit with the engine running, and the valve body's lockup boost valve.

Will an auxiliary cooler fix 47RE overheating?

Only if the root cause is load. If the converter is not locking or the existing cooler is plugged, an extra cooler treats the symptom. Fix lockup and verify at least one gallon per minute of cooler flow first, then add cooling for towing.

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