6T40 Transmission Cooler

If there is a puddle of red fluid under the front of your 2.4L Chevrolet Malibu, Pontiac G6 or Saturn Aura, and the wet spot traces back to the tube that runs from the transmission to the radiator, this is the part you are after. It is a genuine GM transmission oil cooler line, part number 20793279, built for cars with the 6T40 six-speed automatic and the 2.4L four-cylinder. It is a formed steel tube with a rubber hose section crimped in the middle so the line can flex as the engine moves on its mounts. Despite the short product name, this is a cooler line, not a cooler core or a radiator.

What the cooler line does in a 6T40

The 6T40 makes a lot of heat. The torque converter churns fluid every time the car is moving below lockup speed, and the clutches add more heat on each shift. That fluid is pumped out of the case, through one line to the cooler at the front of the car, and back through a second line into the transmission. GM designed this unit around DEXRON VI and a fairly small fluid capacity, so it has little reserve if fluid escapes. A pinhole or a seeping crimp in one cooler line can drop the level enough to change how the transmission behaves well before the warning light comes on.

Symptoms of a leaking or damaged cooler line

• Fresh ATF dripping from the front of the car, often worst after a drive when the fluid is hot and under pressure
• A wet, dirt-caked rubber section or crimp collar on the line, or rust pitting on the steel portion
• Delayed engagement into Drive or Reverse once the level has dropped
• Slipping or flaring on upshifts as the pump starts to draw air at a low level
• A kinked or crushed line after an accident or jack slip, which can restrict flow and push fluid temperature up, sometimes with DTC P0218 (transmission fluid over-temperature)

How to confirm the line is the leak

A 6T40 can leak from several places, and some of them look like a cooler line leak from underneath. Clean the area, drive the car to full temperature, and look again before you order. GM issued a bulletin for fluid leaking from the converter housing area on many 6T30, 6T40, 6T45 and 6T50 vehicles built before February 2013, and an overfilled unit can push fluid out of the vent. Our 6T40 fluid leak guide walks through each of those spots. If the transmission has already been slipping from a low level for a while, read the 6T40 common problems guide too, because running it low can burn clutches that a new line will not bring back.

Fitment

This line is listed for the 6T40 automatic behind the 2.4L four-cylinder in the Chevrolet Malibu, Pontiac G6 and Saturn Aura, and the listing specifies engine code B in the eighth digit of the VIN. Those three cars share a platform and were also built with four-speed automatics and V6 engines, and those versions are not covered by this listing. GM also catalogs a companion outlet line under 20793280, and the listing references both numbers, so you receive the single line pictured. Compare the bends and the fittings at each end with your old line, or send us your year and VIN and we will confirm it is the right one before it ships.

Install notes

• Let the engine cool, place a drain pan under the front of the car and note how each end attaches before you disconnect it. Replace any damaged retaining clip or O-ring rather than reusing it.
• Route the new line exactly along the original path and refit every support clip so it cannot rub on the subframe or vibrate against the radiator.
• If the leak let the unit run low, look at the old fluid. Dark fluid with a burnt smell or debris means the cooler should be flushed and the filter changed; if a teardown follows, the 6T40E rebuild kit with pistons and filter covers the internal soft parts.
• Top up with DEXRON VI only, then set the level hot at the check plug with the engine running, after cycling through the ranges. ATRA lists a fluid temperature window of 85-95 C for that check. Our 6T40 fluid change guide explains the procedure and what a shop charges for it.
• If the car came in slipping and the slip stays after the level is correct, diagnose before buying hard parts. A burnt 3-5-R pack often takes its housing with it, which is when a 6T40 clutch drum belongs on the list.

Is this a transmission cooler or a cooler line?

It is a cooler line: a formed steel tube with a flexible hose section that carries fluid between the 6T40 and the cooler at the front of the car. It does not include a cooler core or radiator.

Will it fit my Malibu, G6 or Aura?

It is listed for the 2.4L four-cylinder cars with the 6T40 six-speed and engine code B in the eighth digit of the VIN. Four-speed and V6 versions of these cars are not covered by this listing. Send us your year and VIN and we will confirm before it ships.

Do I need to replace both cooler lines?

Only if both are leaking or corroded. The listing references 20793279 and its companion 20793280, and you receive the single line pictured, so inspect the other line while you are under the car.

What fluid do I add after replacing the line?

DEXRON VI. Refill, cycle through the ranges with the engine running, and set the level hot at the check plug. Do not just fill until it looks right, because overfilling a 6T40 can push fluid out of the vent.

My transmission was slipping before I found the leak. Will a new line fix it?

A new line stops the leak and restores the level, which fixes a slip caused only by low fluid. If the unit ran low for a long time and the fluid is burnt, the clutches may already be damaged and need diagnosis.

• 6T40 Fluid Leak: Common Spots and Fixes
• 6T40 Fluid Change Cost
• 6T40 Common Problems and Fixes
• 6T40 Delayed Engagement: Causes and Fix