W123 oil cooler lines, tips for not damaging the fittings
 

I have purchased new contitech oil cooler hoses for the 85 300D, however im a bit afraid of loosening the hoses because I have heard the fittings on the oil cooler strip easily.

Anyone have any tips for not damaging the oil cooler?

Thanks

Tons of PB Blaster for a few days before attempting to remove them.

The threads on the cooler fittings don't strip upon removal. It only strips when the installing the cooler lines by force threading them.

What can happen upon removal is the fitting breaks free from the cooler when trying to loosen the lines. Try to get a wrench on both the cooler fitting and cooler line to prevent this. And PB blaster as Kerry noted.



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Heat the nuts with a propane torch, fairly not, and allow to cool prior to the attempt.

Once the nut barely moves............add much more PB or Kroil............and keep working the nut back and forth...........repeatedly............about 200 times..........to allow the PB to work into the threads. Do not attempt to continue removal until the nut is moving decently for a full 360 degrees.

Did I mention to keep spraying that PB........or Kroil........

Patience is a virtue.

Loosen them when the cooler's hot too.

X2

The damage is most likely a wrenching of the threaded portion from the casting whilst undoing it. The nuts on the unions seem to be much tougher than the weak aluminum alloy oil cooler casting.

My recommendation is to take your time and get as much access to the lines as possible. If you happen to be replacing the lines I'd go so far as to say cut through the old lines and make one heck of a mess and then remove the oil cooler from the car before tackling the unions. In that way you know you have as much access as possible.

The only way to be sure to not damage the threads on the cooler is to cut the fittings off the cooler lines with a dremel tool.

Cut a perpendicular slot on the nut so you can use a screwdriver to pry the nut open and off the threads.

I cut the lines off and remove the cooler so I can cut the fittings off at my bench.

The first time I replaced cooler lines I tried penetrating oil and heat while being VERY careful, but the threads were still slightly galled. Since then I cut the fittings off, and the threads are always perfect.

Do you do that in-situ? Do you cut and then kind of un-roll the union from the threaded portion - a bit like breaking open a fortune cookie?

Exactly like a fortune cookie. :) I also cut off the top line first and use my fluid extractor to suck as much oil out of the cooler as I can before cutting the lower line off.

You can cut the fittings while the cooler is in the car, but it's easier to cut the lines and remove the cooler to deal with the fittings IMO. Then you can be comfortable and see everything clearly as you cut the fittings and avoid cutting so deep that you damage the threads or worse.

This also gives you the chance to completely drain the cooler. After doing this the last time, the oil stayed golden for several days before it turned black again. :)

I stripped 3 threads off of mine when removing/backing off the Hose Nut. I found that a Piece of broken off Nipple thread had corroded to the Nut. It acted as a cutter and damaged 3 threads on the way out.
As it happens oxidized Aluminum is actually hard and certainly harder than un-oxidized Aluminum; so, the stuck piece made a good thread cutter.

In the DIY section there is more specific Instructions. One of the Instructions was to use a Dremel type Tool with one of the tiny Cut off Wheels and cut a lengthwise slot on each side of the Hose Nut to the extent that you can get a Screwdriver in the slot, twist and split the Nut.
If you nick the Nipple threads that is not a problem because there is no sealing done by the threads.

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You may need to thin the Backup Wrench you use on the Oil Filter Housing Fittings that the Oil Cooler Hoses screw onto.

Added: At the Junk Yard I tried to remove the Hoses from an Oil Cooler and Stripped the Threads on one of the Nipples; and gave up on it.

I have NEVER stripped an oil cooler fitting.

I have had to remove a cooler from an old rusted out 240 by cutting the lines off the car, and shipping out the cooler to the customer with the ends still attached!

I think Chad has the best idea, and thats the way im gonna do it, ust gotta get a good cutoff wheel for my dremel and i'll be set.

I had no issues changing mine by spraying pb blaster on the fittings each evening when I got home from work.

KROIL is much better than PBlaster; but let either one soak on the threads for 24 hours in advance and you'll have a good chance on not having issues.

if the fittings are dry and rust covered, I'd not only soak them in Kroil or Blaster, I'd lightly tap the flats of the nut with a SMALL hammer, top, sides, bottom, etc. then soak again, then let it soak a day, and repeat for at least a week... longer if not in a hurry.
I've never seen dry lines on any of my cars except my 87 TD, unfortunately... EVERY MB I've gotten has had oil leaks that at a minimum lightly coated each and every part on my cars... the only plus side, is the fittings always come right out.