I'm in the process of swapping out my oil cooler hoses. Had an unusual experience with the nuts on the cooler end which may help someone else. A few weeks ago I tried to loosen the nuts on the cooler. No go. Put PB Blaster on them and waited a couple of days. I then put the 1 1/16" wrench on them and tried to loosen them. I used far more torque than a person should use without a back up wrench and especially on an aluminum part. I did this because I have a spare cooler in the basement and I figured if I broke something, no big deal. Nothing moved. Nuts seemed welded to the aluminum. I planned to cut the hoses, remove the cooler and deal with them off the car. A couple of days ago I tried the top nut again and it came loose with virtually no effort. This morning I tried the bottom one and the same thing happened. Came free with just a few pounds of pressure on the wrench.

Not sure of the physics of the situation. Did the PB Blaster eventually work? Did the very high torque I applied days ago have some effect on the bond between the aluminum and steel? The car has been driven in the meantime so it has gone thru multiple heat/cool cycles. But in any case, it's worth mentioning because those nuts can be a ***** to remove. I had to use a dremel to cut off the nut on the one I had in the basement.

So, if you want to give it a try, put some penetrant on the fitting and wait a few days. Torque the bejezzus out of the nuts trying to get them off. Let them sit for a few days and try again. My case may have been a miracle, but that seems unlikely since both nuts responded to the same treatment.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

PB Blaster surely helped, but most likely the wrenching you did, along with the heat/cool stress of driving worked it in.
I'd advise, soaking with aerokroil/PB blaster, tapping gently on all 6 sides of the nut, then letting it sit a day or so, soaking again, tapping again, then driving repeat for a few days.
I've never had issues with the nuts ON a driving car, but I've NEVER gotten them off of a cooler that is out of a car or in a parts car.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

I followed vstech's advice on the PB Blaster soaking and tapping. I did this for a few days prior to my work and had no issues getting the lines loose. I keep that can pf PB Blaster close now when I am working on the car.

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"Gerwalt" 1984 - 300TD

Heat + time helps wick penetrating oils into tight places.

I have also seen where tightening something a little more along with the above helps loosen stuff.

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84 300D, 82 Volvo 244Gl Diesel

I tried PB Blaster for days and it didn't work. I cleaned it off and put Navel Jelly on the nut. The Naval Jelly are away the rust holding the nut to the steel hose and it came right off.