EVIL ENERGY AN10 PTFE Transmission Line for GM Duramax 01-05 6.6L LB7 / LLY | PTFE Inner Tube with 304 Stainless Steel Braid and Nylon Cover, Design for Extreme Heat, Chemical Resistance & Durability

Q: Why do the factory transmission oil cooler lines leak on a 2001-2005 Duramax?

A: The OEM lines are a steel tube with a short rubber hose section crimped onto each end. Years of ATF exposure and heat cycling harden that rubber, and in cold weather it shrinks slightly away from the crimp collar, so fluid weeps past the joint. Most owners first notice a wet spot behind the front bumper or a film of red fluid running down the passenger-side frame rail, and it gets worse every winter. Because the failure is in the crimp itself, fitting another crimped factory part usually just restarts the clock. Converting to continuous PTFE hose with threaded AN fittings removes the crimp altogether, which is why transmission oil cooler repair on these trucks is normally done as a complete hose swap rather than a patch.

Q: What is a transmission oil cooler, and what do the cooler lines actually do?

A: What is a transmission oil cooler? It is a heat exchanger that pulls heat out of automatic transmission fluid before the fluid returns to the gearbox. On this platform there are two in series: one built into the radiator end tank, plus a separate auxiliary core mounted ahead of the radiator. Following a transmission oil cooler diagram for these trucks, fluid leaves the transmission, flows to the radiator cooler, then through the auxiliary core, then back to the transmission. The lines are simply the plumbing that closes that loop, but they carry the hottest fluid in the system. ATF held above roughly 250°F oxidizes quickly and shortens clutch life, so an automatic transmission oil cooler and its lines are durability parts rather than luxuries.

Q: Is this a repair patch or a full transmission oil cooler hose replacement?

A: This is a full replacement. Splice-type repair kits cut the factory line about half an inch from the crimp and clamp a new rubber section onto the remaining steel tube — cheaper, but it keeps the original tube and adds another joint that can weep later. A transmission oil cooler hose replacement done with AN hose replaces the entire flexible run end to end, so no crimp is left in the circuit. On transmission oil cooler line replacement cost: complete name-brand line sets for this platform typically run about $269-$305 in parts, and shops commonly charge around $200 in labor on top. This transmission oil cooler kit covers the same job at a lower parts cost, with every adapter you might need already in the box.

Q: What comes in the kit, and do I need to buy anything else?

A: The kit ships with three pre-assembled PTFE lines cut to the correct lengths with the hose ends already installed: one 59" hose with 90° ends, one 47" hose with 90° and 45° ends, and one 39" hose with a 90° and a straight end. The adapter set covers every port configuration this platform uses — 6 × 10AN to 7/8"-14 ORB, 2 × 10AN to 3/4"-16 ORB, 2 × 10AN to M22 × 1.5, and 2 × 10AN to 1/2" NPT. You will not need to source transmission oil cooler fittings separately for a stock radiator, an aftermarket radiator, or an added auxiliary core. Beyond the kit you only need basic hand tools, a drain pan, and fresh ATF to top off.

Q: What thread sizes are on my truck, and will these fittings connect?

A: Most 2001-2005 LB7/LLY trucks use 7/8"-14 O-ring boss (ORB) ports, and the six 7/8"-14 adapters cover that configuration completely. Some early LB7 trucks use 3/4"-16 ORB at the transmission instead — the two look similar by eye, so check before you start, and use the two 3/4"-16 adapters if that is what you find. If your truck has an OEM-replacement or aftermarket radiator, the cooler side often uses M22 × 1.5 Setrab-style ports, and many auxiliary cores use 1/2" NPT; both are included. The quickest way to identify a port is to remove one transmission oil cooler line and look at it: ORB ports have a flat sealing face with an O-ring groove, while NPT threads are visibly tapered.

Q: The cooler circuit is low pressure — is a 1250 PSI hose overkill?

A: Under normal driving the circuit sees roughly 20-85 psi, so 1250 PSI sounds like a lot. The number that matters is the cold-start spike: thick cold ATF cannot move through the restrictive cooler cores, and the outbound line can momentarily see 200-260 psi. Those repeated spikes, not steady-state pressure, are what fatigue a factory crimp over a decade. A 1250 PSI working rating with 3750 PSI burst leaves roughly a 5x margin over the worst spike an auto transmission oil cooler circuit produces on this truck. The goal is not running high pressure — it is making sure the hose is never the weak link on a component whose failure can cost a transmission.

Q: Will this transmission oil cooler hose survive Duramax heat while towing?

A: Fluid heading out to the cooler is much hotter than what your pan sensor reports — commonly 80-100°F above sump temperature. A truck showing 200-220°F on the gauge under a heavy trailer can be sending close to 300°F through the outbound line. That is why generic 250°F-rated hose has a poor track record here: it hardens, then weeps at the fitting. This transmission oil cooler hose is rated from -76°F to 446°F, with a PTFE liner that will not swell, absorb fluid, or go brittle from heat cycling, and a 304 stainless braid that holds its shape at temperature. The nylon outer cover adds abrasion protection where the line passes near the exhaust or frame.

Q: Is AN10 larger than the factory line, and will bigger lines lower my transmission temperatures?

A: Yes. AN10 gives a 0.52" inside diameter and holds that bore through the fittings instead of necking down at each crimp, which measurably reduces restriction — most noticeably on cold mornings when fluid is thick. Be realistic about the result, though: on a stock setup the dominant restriction is the cooler cores themselves, not the plumbing, so larger lines alone produce a modest change. A meaningful temperature drop comes when the lines are paired with a larger transmission oil cooler. Treat the bigger bore as removing a bottleneck and creating headroom for a cooling upgrade, not as a temperature fix on its own.

Q: What does the installation involve, and do I have to assemble the hose ends myself?

A: No assembly is required. The three hoses arrive complete with their swivel ends already fitted and pressure-tested, so there is no cutting PTFE, no olives or ferrules to seat, and no special hose shears needed. Installation is a matter of draining the system, removing the factory lines, threading the correct adapters into each port, and connecting each hose to its matching run. The 90°, 45°, and straight ends are oriented for the factory routing, and the swivel design lets you clock each fitting for a clean, stress-free path — worth noting because the 4.5" minimum bend radius means PTFE will not fold around a tight corner. Reuse each factory transmission oil cooler line clip or add cushioned clamps every 12-18 inches to keep the hose off the exhaust and steering components; pulling up a transmission oil cooler line diagram for your model year first makes it easy to match each hose to the right port. Most people budget two to four hours to install transmission oil cooler lines. After the first heat cycle, recheck each fitting for weeps to finish the transmission oil cooler installation properly.

Q: Will this work with an aftermarket radiator, a bypassed radiator cooler, or an added auxiliary cooler?

A: Yes — the included M22 × 1.5 and 1/2" NPT adapters exist specifically for those setups, so no extra parts are needed. Keep the factory series routing (transmission, radiator cooler, auxiliary cooler, back to the transmission) unless you have a specific reason to change it. Some builders bypass the radiator cooler and run a single large core, but the radiator cooler also warms fluid on cold starts, so a full bypass trades warm-up behavior for peak cooling and suits hot climates or dedicated tow rigs. Before you start, confirm the port thread on whatever oil and transmission cooler you are running so you know which adapter pair to use.

Q: Can this hose be used for engine oil, power steering, or fuel?

A: The PTFE liner is chemically inert and compatible with transmission fluid, engine oil, and hydraulic power steering fluid, and the material also resists E85, race fuel, and diesel. This kit is configured and sold for transmission oil cooler line repair and replacement, not as a fuel system assembly — fuel lines carry additional requirements around static dissipation, filtration, and routing that fall outside the scope of a cooler line kit. For fuel plumbing, use a purpose-built fuel line kit with a conductive-liner hose. For an engine oil cooler for transmission-style installation or a power steering cooler, the same AN10 hose and fitting approach transfers directly.