I am replacing my radiator, and I can get the transmission fluid cooler lines loose. Are there any tips out there? When I turn the nut it just turns the whole line, I sprayed it with WD40 but it didn't do much.

Are you using 2 wrenches?
one to hold the fitting (to prevent it from turning) that is threaded into the radiator,
the other to loosen the fitting / collar on the actual trans line...?

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BoatAnchor
'71 Swinger /6-225
SuperSix, EI, front discs, 2.25" exh.

WD40 is not a penetrant. Get some [http://www.kanolabs.com]Kroil[/url]!

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

If you don't have time to wait on shipping, I've found PB Blaster to be fairly effective (or at least far better than WD-40) on flare-nuts as well.

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Used to own:
'82 Dodge D150
Erson 270 Cam, O/S valves, mild port work, ~9.5:1 compression

Currently fighting with an '85 VW Cabriolet

My other passion

Kroil is good stuff.
I've also had good results with PB Blaster. Ugly can, good stuff. Let it soak in a while.
http://www.pbblaster.com/store/moreinfo ... oduct_ID=1

Flare nut wrenches are the right tools to use, using the technique BoatAnchor described.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

To add on to boat anchors method.
If you can, use one or two hands and squeeze the two flare wrenches together. This will prevent the wrench from slipping off and you possibly crimping the line.