Thought I would post on this subject since I only found partial information out there and never a detailed fix. This is the fix for my 2003 Yukon XL 2500.
My rear heater coolant lines started leaking in extremely cold temps from the underside of the vehicle right above the rear exhaust / passenger rear leaf spring. The rubber lines must have deteriorated enough that when single digit to negative outside temperatures cooled them down, they would start slowly dripping and leaving a puddle by the rear passenger wheel. When I cut the factory crimps off the rubber lines, i had orange dry powdery residues inside the crimp and inside the rubber hose where it attached to the flares on the metal lines, letting me know that coolant was leaving the inside of lines and leaking out from the crimps.
My yukon has metal line sets running from the engine bay all the way down the passenger side frame stopping right underneath the rear HVAC heater core. At the end of the metal lines, there are two rubber lines attached, one about 8" long and the other about 12" long that both make 90 degree bends. They attach to two plastic 90 degree quick connect fitting that turn upwards and connect into the heater core from below the vehicle body. From what I can tell in my searches, these line sets were discontinued a long time ago and since the factory crimps are permanent, i am guessing no easy solutions were ever sold to repair them. So here is what I did:
You can probably do this fix without removing the rear passenger wheel and wheel housing liner, but it was not hard at all and made the repair much faster. The rear wheel housing has 6 small screws (3 on the rear and 3 on the front side) and two plastic clips son the inside along the frame area. With that out of the way, you can easily see fitting/hoses.
I used a dremel with a small cut off wheel to remove the aluminum crimps that held the oem rubber hose onto the two metal coolant lines. Once i made a cut down the aluminum crimp i was able to pry it off and then slide off the rubber hoses from the flared fittings. The flares on the metal lines are 5/8" diameter.
On the other end of the metal lines was a quick connect fitting connecting to the heater core. The heater core inlet/outlet metal flare are 3/4" in size. I then disconnected these 90 degree quick connect fittings.
So now I am left with the two metal lines at 5/8" and the two heater core lines at 3/4" diameter. After doing enough searching on the web, I found that Dorman makes 90 degree quick connect fittings in multiple sizes. After buying them, and comparing them to what GM used at the factory, they are almost identical and have the same attachment method. The Dorman 3/4" to 5/8" 90 degree quick connect I used to replace the OEM fitting was Dorman part number 800-419. These worked perfectly and fit perfectly. Since the Dorman fitting reduces the 3/4" down to 5/8", now all I needed was a 5/8" heater hose. I purchased two feet of 5/8" inner diameter hose and (4) small hose clamps (roughly need clamps that can go to about 1" diameter before they tighten down to about 3/4 or 7/8".) I laid my old oem hoses on my work bench and cut my tubing to match with the new fittings, hose clamping the rubber hose to the quick connects. I then installed the new hoses with new quick connects on the the line sets of the truck and made the final hose clamp connections to the vehicle.
You may be able to re use your old quick connect fittings, but since mine were 22 yrs old and these Dormans were basically identical, I decided not to try. The quick connects have a rubber seal inside and I didn't want to chance the old seals leaking after being removed and reinstalled. I did apply a very thin light coating of dieletric silicone grease to the heater core inlet/outlet fittings and to the inside of the quick connects to protect the seals and hopefully avoid any accidental tears. I did not put any kind of grease or lubricant on the plastic to rubber or metal to rubber connections that I hose clamped.
I hope this helps someone who might have the same problem. I saw plenty of posts where people were just either disconnecting and removing the Tee in the engine bay, basically deleting their rear heat, or even people cutting the lines in the rear and capping the connections. If you want to keep your rear heat going and are only having leaks either from the quick connect or rubber hose connections, this allows you to replace them and keep them going. I also attached a picture of my finished job for reference.
My rear heater coolant lines started leaking in extremely cold temps from the underside of the vehicle right above the rear exhaust / passenger rear leaf spring. The rubber lines must have deteriorated enough that when single digit to negative outside temperatures cooled them down, they would start slowly dripping and leaving a puddle by the rear passenger wheel. When I cut the factory crimps off the rubber lines, i had orange dry powdery residues inside the crimp and inside the rubber hose where it attached to the flares on the metal lines, letting me know that coolant was leaving the inside of lines and leaking out from the crimps.
My yukon has metal line sets running from the engine bay all the way down the passenger side frame stopping right underneath the rear HVAC heater core. At the end of the metal lines, there are two rubber lines attached, one about 8" long and the other about 12" long that both make 90 degree bends. They attach to two plastic 90 degree quick connect fitting that turn upwards and connect into the heater core from below the vehicle body. From what I can tell in my searches, these line sets were discontinued a long time ago and since the factory crimps are permanent, i am guessing no easy solutions were ever sold to repair them. So here is what I did:
You can probably do this fix without removing the rear passenger wheel and wheel housing liner, but it was not hard at all and made the repair much faster. The rear wheel housing has 6 small screws (3 on the rear and 3 on the front side) and two plastic clips son the inside along the frame area. With that out of the way, you can easily see fitting/hoses.
I used a dremel with a small cut off wheel to remove the aluminum crimps that held the oem rubber hose onto the two metal coolant lines. Once i made a cut down the aluminum crimp i was able to pry it off and then slide off the rubber hoses from the flared fittings. The flares on the metal lines are 5/8" diameter.
On the other end of the metal lines was a quick connect fitting connecting to the heater core. The heater core inlet/outlet metal flare are 3/4" in size. I then disconnected these 90 degree quick connect fittings.
So now I am left with the two metal lines at 5/8" and the two heater core lines at 3/4" diameter. After doing enough searching on the web, I found that Dorman makes 90 degree quick connect fittings in multiple sizes. After buying them, and comparing them to what GM used at the factory, they are almost identical and have the same attachment method. The Dorman 3/4" to 5/8" 90 degree quick connect I used to replace the OEM fitting was Dorman part number 800-419. These worked perfectly and fit perfectly. Since the Dorman fitting reduces the 3/4" down to 5/8", now all I needed was a 5/8" heater hose. I purchased two feet of 5/8" inner diameter hose and (4) small hose clamps (roughly need clamps that can go to about 1" diameter before they tighten down to about 3/4 or 7/8".) I laid my old oem hoses on my work bench and cut my tubing to match with the new fittings, hose clamping the rubber hose to the quick connects. I then installed the new hoses with new quick connects on the the line sets of the truck and made the final hose clamp connections to the vehicle.
You may be able to re use your old quick connect fittings, but since mine were 22 yrs old and these Dormans were basically identical, I decided not to try. The quick connects have a rubber seal inside and I didn't want to chance the old seals leaking after being removed and reinstalled. I did apply a very thin light coating of dieletric silicone grease to the heater core inlet/outlet fittings and to the inside of the quick connects to protect the seals and hopefully avoid any accidental tears. I did not put any kind of grease or lubricant on the plastic to rubber or metal to rubber connections that I hose clamped.
I hope this helps someone who might have the same problem. I saw plenty of posts where people were just either disconnecting and removing the Tee in the engine bay, basically deleting their rear heat, or even people cutting the lines in the rear and capping the connections. If you want to keep your rear heat going and are only having leaks either from the quick connect or rubber hose connections, this allows you to replace them and keep them going. I also attached a picture of my finished job for reference.
