2013 MKZ Hybrid coolant leak from exhaust manifold

[glocklt4]

115k miles.  I added maybe a 1/3-1/2 quart of coolant ~2mo and ~1k mi ago, wondering what might have cause the loss, then today found a drop of red fluid on the garage floor.  Found a drip on bottom of the block and traced it back to the back of the head.  At first I thought we had a head gasket leak that was coming out the back side of the head, but then, as someone who has owned a boat and had to replace the exhaust risers on it, I realized that the exhaust manifold on the MKZ Hybrid is water (coolant) cooled!  Pretty surprising.  The second from end passenger side header nut is clearly corroded and there are signs of wet and dried coolant down the block from there.  The last nut on the passenger side is also a bit corroded, but not like the 2nd to last since it is on the bottom side.  Wiping the manifold at the bottom there I got some fresher red fluid.  Checked torque of the nuts and 40.5lbft just like they should be.  

 

My suspicion is that the coolant jacket of the exhaust manifold has a small leak, and then it seeps through the gasket (maybe only after motor shutoff and the system is still pressurized because during operation the coolant would get vaporized and go out the tail pipe).  This is a slow leak too considering the time to need more coolant.  The exhaust manifold cooling jacket seems like a sealed system normally, not tied to block cooling direclty.  I don't see any red fluid on the headers themselves though, only from the manifold/gasket/head mating surface.  We've never had the engine overheat, so I don't really suspect head gasket.  If it wasn't for the coolant running through the exhaust manifold, I would have said that head gasket was definitely the issue and maybe it was leaking out of the engine instead of into a cylinder.  Oil looks good too - no signs of coolant.  I will check plugs tomorrow just in case any signs there.  I haven't done any exhaust gas checking of the coolant system either.

 

Has anyone else had this issue?  I found a brand new manifold (which apparently is all welded and has to include cat, ugh), for around $600 on ebay.  Going to call around tomorrow to see if dealerships have heard of this and get some quotes.  If we weren't crazy busy with work I would probably try and tackle this myself, but no time right now. 

 

 

Edited Monday at 03:11 AM by glocklt4

[glocklt4]

Did some more investigating today.  Manually pressure tested coolant system but it dropped slowly from about 15psi to 10psi in 5-6 mins.  Not sure if normal, but also I'm not sure the cap I used is very good.  Tried clamping off the hoses to the exhaust manifold and tested again to see if didn't drop, but same.  When I released clamp didn't see pressure drop, so not a good test there. 

 

BUT, I started the motor up and immediately saw white smoke coming right from the area of the exhaust manifold that I found the red coolant.  Not at the gasket area, but further down on the header pipe where the 4 join together.  It burned off after about 3-4 mins, then as engine cycled it didn't come back.  The smell from that is exactly one we've picked up on for at least 1-2 years in and outside the cabin before, but couldn't figure out.  I thought something plastic touching exhaust burning, or seat heater, a/c, who knows, but never found.... until now.

 

With such a small hole, and a problem that has existed for a while, I'm thinking I might just JB Weld that spot to seal it and see if that fixes.  Dealer would probably charge over $2k to replace entire manifold and cat single unit, but if the leak is just external then $10 fix might work.