The OE lines that come out of the tranny to the radiator and back are metal. It seems to me that if at the pressures and temperatures involved that if the manufacturer could have gotten away with rubber (cheaper) lines, they would have. So why is it OK for an aftermarket transmission cooler installation to use rubber lines? Has anyone had these lines burst? Has anyone opted to get a shop to use metal lines instead? Going up a 10% grade would generate a lot of heat and pressure ... those rubber lines are going to be OK?

It is not only the transmission oil temperature, but the heat from the engine and engine exhaust pipes that determines type of tubing. Metal tubing also dissipates heat while going t the transmission oil cooler. I have not had any burst, but they got replaced because they were getting stiff and brittle.You do not say what kind of rig. Some rigs came with factory metal lines if they were equipped with factory cooler. You maybe able to get factory bent lines from places like O'Reilly auto parts. I was able to get engine oil cooler lines from them.

2006 Trailblazer V8 towing 5000 lb trailer. Chevy says that the existing oil cooler in the radiator is all that is needed, and those to and from lines are metal. I had AAMCO install aftermarket, but they used rubber lines coming out of radiator on way back to transmission. I live in Florida, and since then have towed to Montana and back and forth to Maine, with no problem (that I know about).That said, I used to tow a boat with a 1992 Caprice, and managed to burst the rubber line that went to that cooler by revving the engine in drive with my foot on the brake. The mechanic said it burst because the bend in the line was too tight. I cut the line apart to inspect, and you could see that the oil had eroded the inside of the tubing at the bend.

As Enblethen said, are you sure you need more cooler? People use rubber but often times it's the wrong stuff. You cant put regular old fuel line on like they use on a lawn mower or old car. People have used the old type hose on later model electric fuel pump/injected engines and had fires. Newer systems can run 50 psi or more and require the proper hose. You can cut the cooler lines for after market coolers but be sure to use the best hose, proper fitting preparation and clamping. Also be sure to utilize shielding where needed. I know it sounds like a lot of work because sometimes it is if you want it to last and not be scrambling to get the wife kids and all the valuables out as she goes up in flames. The cooler circuits are not high pressure but they do get hot. The proper hose can stand up to pretty high temps as hoses (proper ones) are used in hydraulic systems all the time. I don't want an aftermarket system cut into my ride but if you have to do it then you have to do it. Its better than overheating the trans. If you are not confident in doing it then you need someone to do it. There's your next problem, finding someone who wont hack it. Sharp pipe ends with tight hose bends can cut from the inside out. I would also say that any hose you put on there should probably not be able to be squeezed together with your fingers.

Soft lines can be built to be just as strong as hard lines.OEMs use hard lines because they can be installed as an assembly and don't require additional steps to secure the lines to keep them in place. Some OEM systems use soft lines as well, especially where vibration needs to be isolated. Even in assemblies with hard lines, there is usually a segment of soft lines because the powertrain moves on the motor mounts, but the radiator and cooler are fixed to the body.As mentioned, just be sure to select the correct soft line for a hot-oil application. Be careful to maintain minimum radii so the hose doesn't kink and restrict flow.If you are really concerned, upgrade so silicone line. They age better and are more tolerant to extreme heat if you are running the lines near exhaust components.

AAMCO should have put the after-market cooler in series with the radiator OEM cooler in the radiator. They should have only used short pieces to connect steel lines to the new cooler.Rubber lines should be rated for oil and pressure. Some places even use vacuum rubber lines. They will not hold up!

transmission cooler lines, rubber or metal? | Good Sam Community

12 Replies

S_more_campers
Explorer
Feb 26, 2014
OEM's use tube for a few reasons; improved cooling/heat management, flow and pressure capacity. No trans cooler line is solid pipe from start to finish, that's just asking for trouble. Even OEM pipe lines will have a flex section to allow the tranny to rock in the mount. As mentioned many times above, use sweeping bends when installing a secondary cooler or replacing lines and you'll never have trouble.
campingsaxplaye
Explorer
Feb 18, 2014
I had added a Hayden transmission cooler, in series, using Hayden connectors between the factory lines and radiator. This was ten years ago on a Silverado 5.3. I never had any trouble with the included rubber lines, but I did replace them 2 years ago after inspecting them. As mentioned before, you just want to make sure there are no kinks or restrictions in the hose and no rub points. I used pieces of heater hose cut down the middle and wrapped around the transmission hose and secured with zip ties to eliminate rub points.
time2roll
Nomad
Feb 12, 2014
Properly bending, flaring and assembling steel lines is fairly labor intensive vs rubber hoses.
So the biggest issue is cost. Assuming the shop used the proper hose the only real hazard is physical damage from the rubber hose rubbing against other items. Inspect carefully and ziptie as needed.
Okie1
Explorer
Feb 12, 2014
Rubber lines are fine, mine actually has rubber from the factory from the radiator to the cooler. Just make sure that you use transmission specific hose, there is a difference. I always run mine through another piece of hose for protection.
Timeking
Explorer
Feb 02, 2014
They did the connections at the radiator as you say is correct. It is a Hayden High Performance 516 for Class A towing 10,000 lbs. I'm towing 5000 with a Chevy Trailblazer. The line is the Hayden hose that comes with that cooler.
enblethen
Nomad
Feb 02, 2014
Why did they run rubber hoses back to the tranny? They should have connected after-market right near the radiator.
What make and model of cooler did they install?
What size of line did they install? Inside diameter.
Timeking
Explorer
Feb 02, 2014
Yes, it is in series, tranny to radiator to cooler back to tranny. As far as "are you sure you need more cooler?" ... I got stuck behind an 18-wheeler struggling up that steep hill into Las Vegas going 15 mph for miles and miles, all the time watching the tranny temp on my ScanGauge creep up to ~220F before I could get around him. I'd think that if I didn't have the aftermarket cooler, I would have fried the transmission pretty much for sure. It got hot, but the oil looked and smelled fine, and have towed another 15,000 miles with no issue. That said, I do the Chevy recommended transmission service every 50,000 miles, as should everyone IMHO.
enblethen
Nomad
Feb 02, 2014
AAMCO should have put the after-market cooler in series with the radiator OEM cooler in the radiator. They should have only used short pieces to connect steel lines to the new cooler.
Rubber lines should be rated for oil and pressure. Some places even use vacuum rubber lines. They will not hold up!
carringb
Explorer
Feb 02, 2014
Soft lines can be built to be just as strong as hard lines.

OEMs use hard lines because they can be installed as an assembly and don't require additional steps to secure the lines to keep them in place. Some OEM systems use soft lines as well, especially where vibration needs to be isolated. Even in assemblies with hard lines, there is usually a segment of soft lines because the powertrain moves on the motor mounts, but the radiator and cooler are fixed to the body.

As mentioned, just be sure to select the correct soft line for a hot-oil application. Be careful to maintain minimum radii so the hose doesn't kink and restrict flow.

If you are really concerned, upgrade so silicone line. They age better and are more tolerant to extreme heat if you are running the lines near exhaust components.
azrving
Explorer
Feb 02, 2014
As Enblethen said, are you sure you need more cooler?
People use rubber but often times it's the wrong stuff. You cant put regular old fuel line on like they use on a lawn mower or old car. People have used the old type hose on later model electric fuel pump/injected engines and had fires. Newer systems can run 50 psi or more and require the proper hose.
You can cut the cooler lines for after market coolers but be sure to use the best hose, proper fitting preparation and clamping. Also be sure to utilize shielding where needed. I know it sounds like a lot of work because sometimes it is if you want it to last and not be scrambling to get the wife kids and all the valuables out as she goes up in flames.
The cooler circuits are not high pressure but they do get hot. The proper hose can stand up to pretty high temps as hoses (proper ones) are used in hydraulic systems all the time.
I don't want an aftermarket system cut into my ride but if you have to do it then you have to do it. Its better than overheating the trans.
If you are not confident in doing it then you need someone to do it. There's your next problem, finding someone who wont hack it.
Sharp pipe ends with tight hose bends can cut from the inside out. I would also say that any hose you put on there should probably not be able to be squeezed together with your fingers.