Oil Cooler Seal Leaking

[dtoelke]

Anybody else ever had trouble getting a cooler sealed properly?  My oil cooler developed a crack in the core a couple weeks ago during a cross country so I replaced it with an A&P in northern Nevada.  When I returned I noticed there was oil dripping (slowly) out of the cowling so I pulled it off to investigate.  Washed clean and traced the leak to the lower right bolt on the new cooler.  No leaks were coming through the outer sealing surface.  After trying to plug the leak with gasket maker injected before rebolting (didn't work), we decided to pull the cooler off again and regasket (with new paper of course).  I made damn sure we had a healthy coating of sealant on all surfaces before we put it back on but low and behold it is still leaking (albeit much slower than before) and also very slightly from the bolt above that as well.

 

Could anybody share tips on getting a good seal on the gasket?  The oil cooler is particularly tough since it's position makes it difficult to avoid accidentally dabbing the sealant by bumping the cooler around during install.  We used high temp silicon as the sealant (any other recommendations).

[Piloto]

Verify the leak by putting air pressure (60 psi) into the oil cooler and submerging it into a water bucket. Check where the bubbles come from. Many oil coolers are made of solderable material such as copper or brass. See if you can solder where the bubbles come from. Sealant does not hold under pressure.

José

[dtoelke]

I replaced the cooler with a new one.  Sorry for the confusion.  The new leak I'm talking about is around the mating area.  Somehow the gasket is not completely sealing.

[jetdriven]

For paper gaskets like that we always use permatex aviation sealer. Indian head is the same thing. It's a gasket shellac which is miscible in oil, silicone or Teflon tape can find its way to a bearing passage and ruin the engine.

[helitim]

Have you verified that the mating surface on the new cooler is not out of shape/bent somehow? Even if it is new, it is possible to have a defective surface.

[dtoelke]

Yes the surface looks fine.  Byron, is that the "Permatex Form-A-Gasket Aviation No. 3 Sealant Liquid"?  I also found the Permatex Indian Head Gasket Shellac at Autozone.  Which do you recommend?  I see TCM recommends CRC 401504 Copper-Coat Liquid.

[jetdriven]

Yes, those two are so similar they even smell the same, im pretty certain they are the same, and have used both on my plane. However, if TCM recommends the 401504 I'd use that.

[dtoelke]

Ok, thanks guys!

[dtoelke]

I was hoping I wouldn't have to post in this thread again but...

 

Before I replaced the gasket today I called up a MSC down in LA to double check the bolt torque specs.  We'd been using 70 in-lbs because that's what the A&P who originally repaired up in Nevada had looked up.  Well it turns out he was way off which is probably the main reason it wasn't sealing correctly.  TCM was showing 100-110 in-lbs.

 

Anyways, I replaced the gasket and used the CRC copper coat on both sides and went to tighten the bolts...  all of them went nice and tight except the lower right corner, which I couldn't get past 80 in-lbs without feeling the threads begin to strip.  Has anyone here dealt with stripped (or nearly so) aluminum threading on the block?  What kinds of strategies do you employ to avoid having to retap?  As I mentioned before it's not completely stripped since I can get it to 80 in-lbs which is still fairly tight.  I'm going to speak with a couple other local A&P's but I was hoping somebody here might have a good suggestion.

 

Thanks in advance!

[Guest]

You'll have to remove the cooler, clean up the area and install a Heli coil then reinstall the cooler.

Check out TCM SB96-7C page 7 for torque value for your cooler

Clarence

[dtoelke]

Thanks Clarence!