Oil Cooler Question

[Kenneth Gear]

I appear to have a minor leak in my oil cooler.  It seems to be leaking at or near the top hose connection.

Two questions...

1) The hoses were recently replaced.  Is there a gasket, washer, or ring at that fitting that may be the source the the leak.   I don't seem to have a wrench large enough (yet) to remove the hose and check.  

2) Is an oil cooler repairable like a radiator or must I get a new one?

Thanks




Ken G
1971 280 SL
Silver/red

[ja17]

Hello Ken,

It is a compression fitting and there are no seals. A little grease may help the parts mate and seal tightly. Do not use any sealer since it may end up in the oil circuit.

These oil coolers are steel. The fittings are most likely brazed in place. Your problem is more likely a loose fitting.

The fitting on the hose is 27mm and the stationary fitting on the cooler is 22mm (skinny).  Tightening or loosening these lines should be done with these two wrenches, so as not to damage the oil cooler. You can convert these to the nearest inch sizes which will work fine since metric sizes this large may harder to find.  You may have  to grind the 22mm  wrench so it is thin enough to fit into the narrow space.
A large adjustable wrench will also work on the 27mm fitting.


Joe Alexander
Blacklick, Ohio

[George Davis]

Ken,

I had a similar problem when I replaced my oil cooler hoses.  The nuts on the new hoses are deeper than the originals and need to screw on farther to get a good seal.  The old paint and crud on the cooler threads made the fitting feel tight, but it was really slightly loose and leaked.  It's been a while, but I think I just took a wire brush and cleaned the threads well and put it back together.  No leaks since.  I think I redid the bottom fitting too, but may have waited for the next oil change since it wasn't leaking.  Stick something into the cooler fitting while cleaning to keep junk out of the cooler.



George Davis
'69 280 SL Euro manual

[Kenneth Gear]

Thanks for the sizes.. I'll ge the correct sizes and try to tighten down the fitting later today.

I appreciate the advice

Ken G
1971 280 SL
Silver/red

[Kenneth Gear]

I got the correct wrenches.  Used a skinny 7/8" in place of the 22mm which worked fine. (Looks like a 1 1/16 would replace the 27mm)

However, I was unable to budge the fitting - it was already super tight and wouldn't budge.  The leak definately seems to be coming from the fitting -- it appears that oil is spraying out of the fitting as I can see splashes of oil on the undderside of the hood and on the battery etc.

I can't seem to get it to leak during idle so I am unable to watch it while the car is running to ponpoint it exactly.

Any ideas?

Ken G
1971 280 SL
Silver/red

[George Davis]

I'd guess the mechanic super-tightened the fitting because it leaked when first installed.  The fitting should be taken off and the threads cleaned and the sealing surfaces inspected.  Super-tightening of hydraulic fittings should never be necessary.  If cleaning the threads and retightening doesn't solve it, I believe there may be repair seals that can be used to seal between the sealing surfaces.  A hydraulic supply shop can advise you.

You could try heating the fitting nut to loosen, but be careful to avoid damaging the hose.  A good penetrating oil might help.  At this point you absolutely need to use the backup wrench.

Good luck!

George Davis
'69 280 SL Euro manual

[Kenneth Gear]

I'll try removing, cleaning and reinstalling the fitting.

If that doesn't work and it turns out to be the cooler itself, can anyone tell me how difficult it is to replace?  Must the hood be removed?  Can it be removed from below?

Ken G
1971 280 SL
Silver/red

[Kenneth Gear]

I was able track down my oil cooler leak, it is not a leaking hose as I suspected rather it is leaking at the top of the oil cooler directly behind where the hose fitting is.  There is the hose fitting, a nut for the fitting which is attached to the oil cooler, and a "cap" peice of metal convering the top of the oil cooler. I can wedge a small mirror underneath to see a drip coming from behind the metal cap on the oil cooler.

Does this mean I need an entire new  cooler?  If so, any tricks to installing one?  Does it come out from under the car?





Ken G
1971 280 SL
Silver/red

[ja17]

Hello Ken,

Normally the Oil cooler is removed along with the radiator. I suspect that you may be able to coax the unit out without removing the radiator, but you will probably not save any time. Remove the battery, and air filter canister and then the 10mm radiator mounting bolts. The oil cooler is attached to the radiator by two long carriage type bolts. Of coarse all the hoses must be disconnected.

These oil coolers are very pricey new.  I would take it to a radiator shop and explain that the leak must be brazed (not soldered).  These units must hold over 100psi.  As long as your oil cooler is not rusty it should be an easy fix for someone good with a brazing torch.



Joe Alexander
Blacklick, Ohio

[Sven]

I have an oil cooler question.  My cooler sprung a leak and I was able to obtain a used cooler from a sedan.  However, the cooler is identical with the exception of the two bolted connections along the driver side of the cooler (not bolts to radiator on passenger side of cooler).  the sl cooler had threaded holes or a nut welded inside, the sedan cooler does not.  the sedan cooler has holes the match in location, but are just open holes (i.e., nothing to thread the connecting bolts into).  

what have any of you guys done to secure the connection on the driver side of cooler.  use self taping screws, welded a nut, etc?  

thanks in advance

[ja17]

Helllo Sven,

Can you just 10mm nuts on the other side?



Joe Alexander
Blacklick, Ohio