I have a leak at my lower oil cooler threaded connection. I've checked the hose itself, and it seems not to be weeping or leaking at the crimp, but down at the threads. I'm getting a puddle about the size of a half dollar on my garge floor each night.

I've heard all sorts of horror stories about stripping the AL threads in the cooler. Is this something I can simply tighten, or am I looking at a complete teardown? Is there a sealing ring or crush washer between the cooler and the hoses?

Thanks,
Bob
'82 300D

No crush washer or sealing ring just a taper fit. Try and tighten carefully.
Are you sure it's not from the hose?

There is no washer or sealing ring. It is a compression fit.

You could try to take off the collar and remove the fitting. Clean them up and reattach.

I've never heard of stripping problems. Are we sure people aren't overtightening?

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

The cooler line is threaded onto the cooler, unless its cracked it shouldn't be leaking. Is the cooler line original? Time for some new ones it seems.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Clean the immediate area with laquer thinner well. It evaporates to a dry surface very fast and thats why it is prefferable. Have a very hard look for the seepage point or leakage. You might have a vibration crack in the area. It is just a possibility and apparently unusual. Just cannot see if sealed up before why a leak would start beween the threads. I guess corrosion perhaps come to think of it but you want an exact location of the leak before deciding anything in my opinion.

If it is the original hose, I would be reluctant to tighten it at this point. If there is any corrosion between the alloy threads on the cooler and the steel threads on the hose, you run the risk of pulling the alloy threads off. I would seriously consider replacing the hose by cutting off the steel female fitting.

Rick

__________________
80 300SD (129k mi) 82 240D stick (193k mi)77 240D auto - stick to be (153k mi) 85 380SL (145k mi) 89 BMW 535i 82 Diesel Rabbit Pickup (374k mi) 91 Jetta IDI Diesel (155k mi) 81 VW Rabbit Convertible Diesel 70 Triumph Spitfire Mk III (63kmi)66 Triumph TR4a IRS (90k mi)67 Ford F-100 (??)

OK, I checked for oil residue on the hose itself or on the crimp and I find none (just dirt).

This leads me to believe that the seepage is coming from the threads at the nut. I'm going to degrease and try to get a better sense of the exact location.

If you are replacing the hose, I also would recommend cutting the fitting off. Or at least put a good gash in it to weaken it. You don't want to ruin the aluminum threads underneath. While taking mine off & holding back the male aluminum fitting while loosening the female steel fitting on the hose, the aluminum part of the fitting broke off inside the steel one. UGH! Be careful, Paul.

__________________
1984 300CD red/blk 290,000 partial resto
1980 240D 4 sp Brn/palomino gone
1997 Mazda Miata STO edition wife's baby
1988 Lincoln Mark VII LSC next resto
1986 Subaru GL wagon daily
1993 Isuzu pickup field beater
2008 Honda Civic EX-L 5sp wife's new car
1978 Honda XL350
1974 Honda XL70 my Calif. ride in HS

OK, here's the update. Soaked with penetrating oil for two hours. The nut turns in both directions, and doesn't seem to
be all that tight.

Does anyone have a torque spec for these nuts (at the cooler)?

Thanks,
Bob
'82 300D

Just slightly tight. Just stick a wrench on it and snug it. These are like threaded pipe fittings, you should be able to screw it on by hand and it shouldn't leak.

Something isn't right.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Understood. I'll stop now and collect myself.

Anyone have suggestions as to where to go next?
Pull the oil cooler and examine the threads for cracks
under magnification? Is it possible the fitting on the
hose side of the joint has gone bad?

Thanks for any help
Bob
'82 300D

I'd pull them apart and inspect the cooler fittings. More likely then not the lines are failing at the crimp, and somehow it looks like the leak looks like its coming from the threads.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Double-check for burrs where the tapered portions fit together. A light touch with emery cloth should take care of them.

I found that cleaning the threads real well on both the hose and the cooler, then threading and tightening by hand as much as possible works best. After that, a light touch with a wrench is all that is needed.

__________________
Sam

84 300SD 350K+ miles ( Blue Belle )