HELP - COOLING SYSTEM ISSUE / COOLANT BOILING

[Hurricane321]

Hoping I can get some advice here... I have a 2017 Ecoboost Premium Perfomance Pack car with Roush CAI and Roush Stage 1 tune. Its my daily driver, I've put every mile on since new up to the current 135,500K on the clock. The car got a warranty short block at 60K and has had a head gasket since, also warranty, all work performed by Elder Ford in Tampa, and general maintenance is done by me, so I've always been very in-tune with thats going on with the car. So recently, I had a bunch of items come up at once, battery, plugs, oil change due...among other things but those have nothing to do with this...so I popped in a new AGM battery 2 days ago after milking / limping my previous motorcraft battery along for about a month thanks to a jump pack and trickle charger...I had also been pulling a random cyl 1 misfire and had about 70K on the NGK Ruthenium plugs that I installed shortly after the warranty short block went in and had a stutter / miss that you could feel at times under WOT....so this weekend I did my oil change and swapped the plugs out with the NGK 6510 (HR 7) plugs....the plug for cyl 3 came out soaked in oil, all others were fine, all gaps had grown to .40-.44...car seemed happy with the new plugs and fresh lube, but then yesterday morning I found a coolant puddle under the car...no visible leaks, but the fans and area directly under the coolant reservoir (degas bottle) were wet...immediate thought was maybe the bottle has a small crack at the seam or by the neck on the bottom, but couldnt find any clear signs of drips or anything. Took the car for a ride, all temp gauges reading normal ranges, no signs of over heating, but when I came home and shut the car down, I could hear the coolant boiling in the bottle, popped the hood and again had coolant on the fan, components, and pan directly below the bottle and no visible drips leak or source, but I recognize the boiling coolant is new and obviously an issue regardless of if the gauges are reading good or not....I did notice the cyl head temp reading on the digital cluster is running between 190-220 and seems like the fans arent kicking on until it gets up to 218-220, then it will quickly drop back down...I dont recall my normal operating temp living in the 200-220 range much in the past, more like 180-210 maybe...my first thought was maybe the thermostat was going bad or hung open, but as easy as that maintenance has been in the past on alot of vehicles I've worked on, its apparently burried on the back of the block by the firewall on the S550 EB and looks to be a real PITA to get to, so I'm hoping its not that. I did replace water pump about 15-20K miles ago with Napa parts, no apparent issue there....additional note : AC high side hose has gone bad at the crimp, so I'm not running my HVAC system at the moment to avoid potentially damaging the compressor with an empty system... thoughts have been either thermostat, fan relay, maybe a sensor somewhere, but I'm otherwise stumped as to why im boiliing coolant yet reading fine on the gauges....hoping someone can speak on a similar past experience or help point me in the right direction here....

Also, I'm aware of the issues with cylinder 3 excessive heat due to proximity to the turbo, thats where all the head gaskets fail, and the cylinder that pretty much has all the problems...I'm not getting head gasket symptoms tho in the sense that I have no oil / coolant mixing, im not getting random temp spikes on the actual gauge itself like the first time the HG failed, and aside from what its pushing out while boiling, which does puddle but isnt massive, im not seeing much drop in my coolant levels either...so while I feel like the head gasket has the potential to always be a problem, I dont feel like its my cause here unless its just the first sign....

If this were to be a head gasket leak that hasnt turned into a full blow "blow out", is blue devil safe to use in a turbo car? I'm out of warranty so at this point, assuming safe, I'm more inclined to try the bottle before I rip the top end off and do a HG if that were the likely culprit.

I appreciate everyones thoughts on this, thank you in advance.

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[MuddyPaws]

Possible degass bottle cap not holding pressure? May want to do a pressure test on cap and system.

 

[ORRadtech]

Are you sure it's boiling and not just bubbling from combustion/exhaust gas pressure? A head gasket can fail in several ways. Mine had a micro leak into the combination chamber. I never saw any coolant anywhere. Just had the #3 misfire and a borescope on a cold engine would see tiny fleks of coolant on the piston edge. Never any coolant in the oil above a microscopic level. Blackstone found it, but it wasn't enough to visually change the oil.
If you're doing the troubleshooting yourself, you might consider picking up one of the testers that detect combustion gas in the coolant. And/or borescope the offending cylinder.

 

[Hurricane321]

Thank you for the replies - turns out it was the degas bottle cap....the day I posted I left work and had a bigger puddle mark under the car than previously so I stopped and checked and my coolant level was low, when I went to Advanced for coolant, I thought that since I didnt see any leak source from the bottle, but common sense said the source could only be the bottle based on where was wet, I figured I'd replace the cap just cause its cheap and why not have the peace of mind...well when I pulled the old cap I found the bottom had broken off at the o-ring, and the o-ring stayed in the neck when I pulled the cap, so I replaced with new aftermarket and havent had the issue since. Avg running temp is hanging about 10-15 degrees cooler and not more bubbling or boiling in the bottle....

Obviously I know I've still got something going on w/ cyl 3 but also understand its almost unavoidable with this engine due to the excessive heat around cyl 3 from the turbo basically being mounted to it on the outside of the block....at least thats what ford said when they replaced the last head gasket....

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