4L60E 6AN PTFE Transmission Cooler Line Kit, 52 Inch

Rust usually gets the factory cooler lines on a Silverado, Sierra, Tahoe or S10 before it gets anything else under the truck. The steel tube rots at a frame clip, the crimped rubber section starts to weep, and a few ounces of fluid at a time disappear onto the driveway. This is a 52 inch length of -6AN hose with a PTFE liner and stainless steel outer braid, sold with the end fittings shown, for a short cooler run on a GM 4L60E or 4L65E, or on an older 700R4, 200-4R, TH350, TH400 or Powerglide build.

What a cooler line does on a 4L60E

Fluid that has picked up heat in the converter and the clutch packs leaves the case through one cooler port, passes through the cooler in the radiator tank or an auxiliary cooler, and comes back through the second port to feed lube oil to the gear train. If a line leaks, kinks or collapses, that return flow drops. The 4L60E then runs hotter and lower on fluid at the same time, which is exactly the condition that cooks the 3-4 clutch pack this unit is known for. A cooler line is a cheap part protecting an expensive one.

Why PTFE instead of rubber

• The PTFE liner does not swell or go soft in ATF, so the hose keeps its bore after years of hot fluid
• Listed for -76F to 500F, which matters on a tow rig where the line passes near the exhaust or the catalytic converter
• Rated 3000 psi working and 10000 psi burst, far beyond what a cooler circuit sees
• The stainless braid resists chafing where a line rides on a frame rail or crossmember

Signs your cooler lines need replacing

• Wet, crusty fittings at the case or the radiator, or a drip that leaves red spots after the truck sits
• Rust scale or pinholes in the steel tube, usually at the clips along the frame
• Swollen, cracked or soft rubber sections near the crimped ferrules
• Fluid level that keeps dropping with no leak at the pan, and shifts that flare once the truck is hot
• Dark, burnt-smelling fluid after towing, a sign the cooling circuit is not keeping up

How to confirm the problem first

Clean the case fittings, the radiator fittings and the whole length of both lines, then run the truck to full temperature and look again. Check the fluid level hot. If the unit is already slipping in third and fourth or the fluid is full of friction material, new lines will not bring it back; the 4L60E common problems guide walks through which symptoms are internal and which are fluid loss. Van owners can also check the Astro van problems guide, where cooler routing runs close to the engine.

Fitment

The included fittings cover 9/16-18 UNF, 3/8-18 NPT and 1/4-18 NPT ports, which handles most older GM cases, the 4L80E from 1995 on, and the Ford C6 and AOD. The 4L60E and 4L65E case is different: its cooler ports are a 1/4 inch NPS straight thread, so you need a -6AN to 1/4 NPS adapter at the case end. That adapter is not included. If you would rather have the case adapters in the box, the 6AN cooler line kit with 15 ft of hose and NPSM adapters is the complete package. 52 inches is one short run, enough for a case-to-cooler jumper on a truck where the cooler sits close, not both full-length lines to the front of the radiator. Measure both runs before ordering, and send us your year and VIN if you are not sure what ports your truck has. Everything else for this transmission is on the 4L60E parts page.

Install notes

• Lay out the route with a piece of wire first. PTFE hose is stiff and kinks if you force a tight bend, so give every turn a gentle radius or use an angled hose end.
• Wrap the cut point in tape and cut through the braid with a cutoff wheel so the stainless strands do not fray. Blow out the hose before assembly.
• Seat the olive and socket fully before torquing the AN nut. Use thread sealant on tapered NPT threads only; straight-thread ports seal on the fitting, not the threads.
• Keep the hose clear of the exhaust and anything that moves, and clamp it so it cannot rub.
• Top off with Dexron VI, run the truck to full temperature and check every joint again after the first heat cycle.
• Running a big auxiliary cooler or a high-stall setup? The 8AN braided cooler line kit gives a larger bore for higher flow.

Will this hose thread straight into my 4L60E case?

No. The 4L60E and 4L65E case uses a 1/4 inch NPS straight-thread cooler port. You need a -6AN to 1/4 NPS adapter at the case end, which is not included with this hose.

Is 52 inches enough for both cooler lines?

Usually not on a full-size truck where the radiator is several feet from the case. The 52 inch length suits one short run, such as a jumper to an auxiliary cooler mounted near the transmission. Measure both feed and return routes before ordering.

Why pick PTFE hose over rubber braided hose?

PTFE does not swell or soften in ATF and is listed for -76F to 500F, so it is the better choice when the line has to pass close to the exhaust or the truck tows heavy. It is stiffer than rubber hose, so it needs gentler bends.

Which fluid do I use after replacing the lines?

Top off with Dexron VI, which is the current GM service fluid for the 4L60E and 4L65E. Check the level with the fluid hot and the engine running in park.

Does it fit a 700R4 or TH350?

Yes. The fittings include 9/16-18 UNF, 3/8-18 NPT and 1/4-18 NPT threads, which cover the common ports on the 700R4, 200-4R, TH350, TH400 and Powerglide. Check your case port before you order.

• 4L60E Common Problems, Symptoms, and What to Actually Do About Them
• 4L60E Astro Van Common Problems and Fixes
• 4L60E Chevy S10 Common Problems and Fixes
• 4L60E Camaro Common Problems and Fixes