Transmission cooling line popping out of radiator

Hi people. I’ve written on here a couple time relating to this issue. My lower transmission cooling line keeps popping out at my radiator. I really don’t want to replace my lines. It was 107 here today and I spent 10 hours in my garage.

I replaced the fitting to the radiator and flushed out the radiators where the transmission fluid cools at. I changed the transmission filter and fluid just now.

What I’m wanting to know is if it is common for the ends of the transmission lines (where they plug into the radiator) to become worn and pop off? The end of the line looks fine. It seems to be in there fairly snug.

I’m tempted to cut the end of the line off and attach another using tubing and clamps.

I should mention the radiator is a replacement AcDelco I put in a couple years ago but I’m not sure where the fittings came from. I don’t think they’re original. They don’t match the ones I just got from a local Pick and Pull.

Maybe its not snug enough…

“I’m not sure where the fittings came from. I don’t think they’re original. They don’t match the ones I just got from a local Pick and Pull.”

This may be your problem. If the fittings are the correct thread and on snug they won’t pop off. If the fittings are close but not exact you may be able to screw them together and it may look good but under pressure they pop off.

When my kids were in school in the 70s and 80s and I was working on old rusty slant 6 Mopars to keep them in transportation, I learned not to mess with the fittings into the radiator. I would just cut them off 3 " from the radiator and put them back with a piece of fuel line and hose clamps. Never had a problem with one coming looser. Do modern transmissions have higher pressure to the radiator than torqueflights?.

When we junked one of these $200 to $400 cars, I always pulled parts including hoods and trunks for sheet metal so always had parts on hand.

When you pushed in the cooler line, did it click . . . ?!

There’s no ifs ands or buts

Either it did . . . or it didn’t

Did you lose the clip which is part of the fitting . . . ?

If so, the line will never stay locked in place

Hi sorry for the slow response. It does click in and the c clip is in there

Make sure the cooler line goes into the fitting perfectly straight, so that the flange on the line clicks behind all three points of the retaining ring (see pic). It may take substantial force to push all the way in.
Trans Cooler Line Fitting
Note that, unlike in the pic, all three parts of the ring should protrude into the fitting the same amount.

When installing the retaining ring onto the fitting, GM suggests rotating it in place rather than pushing straight on, so as not to stretch the ring.

Make sure the flange on the tube is in good condition, flat with nice crisp edges. If the flange is bent or rounded on the edges, the retainer may not hold it in place well.There should be a plastic cap that snaps over the fitting. I don’t know if this is just a dust cover, or if it actually helps keep the retaining ring from expanding and allowing the tube to come loose. According to GM, there should be a yellow identification band on the tube that should be hidden within the fitting when properly connected. If that band is visible outside the cap, the tube may not be clicked in all the way.

The cooler lines appear to be clamped to the engine. Make sure any engine movement isn’t causing a tugging on the lines.

Thanks that was helpful. I’m not confident the flange isn’t worn. It doesn’t seem to be…
It does snap into place. It’s weird because it began happening out off the blue.
I’m tempted to cut another line to ensure I have a good flange and then connect it to the old line, with the end cut off, with tubes and clamps. Do you think that could be a permanent solution? I believe the lines should only be pushing 15 psi.

I’m not sure what the 4L60E cooler line pressure is. A bit of web searching doesn’t yield definitive results, but I’ve seen numbers mentioned up to 100psi under certain circumstances, especially when the TCC is engaged. The “normal” range might be about 20psi with the TCC disengaged.

Rubber hose should be okay. Aftermarket add-on coolers are generally connected with rubber hose. Just make sure the hose is rated for transmission fluid/cooler use. It seems people have gotten away with just clamping the rubber hose to the metal lines, but I’d rather see some sort of bead on the tube ends to aid in hose retention.

If the tube end is damaged, rather than rigging it with hose, it wouldn’t be very expensive to buy replacement steel line(s).

You could also try putting a hose clamp around the outside of the fitting (either over or in place of the plastic cap) to make sure the retaining ring stays fully in place.

Thanks. I might replace the line. I bought one and saw where it connected to my transmission and realized I would have to take off my exhaust and I don’t know if I would even then have enough room to get my hand up there. I wish the connection was lower.

The service manual says to remove the exhaust crossover pipe (which is actually part of the whole manifold pipe and cat assembly) and the transmission support assembly, then carefully lower the transmission to gain access to the cooler line fittings. Does seem kind of a pain, especially if the exhaust pipes don’t come apart nicely due to rust.

It’s pretty rusty. Looks like I’ll be connecting it with hose. Thanks for your help.

I’ve seen a lot of problems when this is done

Unless you flare the line properly . . . the line where the rubber hose will slip over . . . the hose will eventually blow off. It could be a few years, but it WILL happen. Double clamping won’t prevent this from happening, either. I don’t know why some guys persist in thinking double clamping will prevent all future problems

Thanks. I was just reading about how too flare lines. Any tips for flaring properly?

Those tips you were reading . . . were they for flaring brake lines?

If so, that kind of flare is the wrong kind for this particular application

It was. Whats the name of the flaring procedure I should be doing?

Is it swedging?

You can join two sections of the steel tubing together by double flaring the ends and using a union.

That’s why I said above: “I’d rather see some sort of bead on the tube ends to aid in hose retention.”

This is known as a bead, just like those on coolant tubes and low pressure fuel tubing, et. al.:
Tube Bead

There are hand held tubing bead rollers available. Some high end multipurpose flaring tools with the proper grip dies can do beads too. But they’re all a bit expensive for a one-off job. Maybe some parts stores that rent tools would have flaring tools? I wonder if a bubble flare at the end of the tube would work.

@Nevada_545 has a good idea with the flaring and union, but it wouldn’t necessarily have to be a double flare. Double flaring can crack the tubing if it’s too hard. Single flaring should be adequate for low pressure use, like for AN fittings. I’ve seen mention where some people have used compression fittings/unions successfully (if the tubing isn’t too hard to deform properly). No flaring needed.

What you pictured should work, in my opinion

That said . . . I know a lot of people who do NOT make that bead. These are the same guys who cut off the pipe flush, double up on hose clamps and pat themselves on the back

And later on, the hose blows off, even if it’s a few years down the road, when the guy is off the hook

And that is one of the the reasons why alarm bells go off in my head when I encounter vehicles with added aftermarket transmission coolers. Because a significant portion of guys do NOT do the job properly.