I have recently acquired a truly gorgeous 2009 HCH. ~139k miles, paint mostly intact, and a nearly spotless interior to boot. Service history is vaguely promising, having a number of IMA-related repairs done in her first few years of ownership, although a crash in ~2020 led to the a/c condenser and bumper cover being replaced. Beyond that, her history is largely unknown to me, which makes diagnosing her that much more of an undertaking.

Primary concerns and notes:

• The 12v is dead and the battery cables are loose. Any codes that may have assisted me in this endeavor are long gone. A quick jump gets her running no problem though, and she starts with the IMA motor rather than the starter, despite the cold weather.
• No cabin heat. Absolutely none. Further diagnosis needed.
• She had very little coolant on first start. Topped it off (aggressively), bled (albeit without loosening bleeder screw, I hate burning my hands trying to get to it), etc. Minimal debris returning from radiator.
• Seemed to hold temp fine on first starts, fans engage when expected. After adding coolant, driving ~1 block, overheated minorly. Shut down asap to avoid (further) damage.
• Smoke? Vapor? It's been a comfy ~30 degrees up here (0 for all you non-US folks) so I can't say for sure, but something creeps out of any openings to coolant passages once she's been running for several minutes. This includes seeping out of the coolant overflow reservoir. Smells faintly of nail polish remover and hot coolant - gasoline? Old gasoline?
• Minor intake leak between air box and manifold, rubber boot decaying. Seems to be logical source for whistling noise while running, need to confirm.
• Odd whirring noise from corner of firewall/driver's side fender. Electric water pump? Brake system? Undetermined at this time, but definitely worth noting.
• Angry coolant. After filling, bleeding, filling, and shoving radiator cap on, coolant began to violently plummet into the overflow reservoir. Terrifying. Why is she so angry? Why is the coolant over-pressurized? (I probably overfilled it a smidge but wow)
• Oil smells/tastes/looks normal - no evidence of "chocolate milkshake"

Current vague game plan for diagnosing:

• Bring my **** code scanner. Can't believe I forgot it.
• Run HVAC self-diagnosis, ensure blend door is moving as anticipated.
• Inspect/test electric water pump?
• Pressure test coolant system, verify/identify leaks or other issues.
• Narrow down source of weird whirring noise - run with/without HVAC on, apply brakes, etc.
• Compression test?
• Attempt to determine function of water pump & thermostat
• Bleed cooling system more thoroughly, despite general suckiness of this endeavor
• Remove EGR plate from intake, inspect coolant passages, attempt to remove carbon without dismantling intake manifold.

As it stands, I'm willing to bet this is an "easy" diagnosis - the head gasket is blown, the end, that sucks. I'm hoping that isn't the case - largely because I've been "almost done" with a head gasket job on another Civic for like six months. My other guesses include issues with the EGR/intake system, as the presence of very angry coolant and the general stench of potentially unburnt fuel seems to make that a feasible explanation. I still need to get the Carfax for her and figure out if/when the spark plugs were last done. But I know these cars are weird. I know every time I've set out to diagnose a seemingly "easy" issue, the actual cause has been something absurd. So with that said, if anybody here has any other suggestions for things I ought to inspect/probe/dismantle/blame for my problems, I'm all ears. I'll be sure to keep updating this thread regardless.

Thanks in advance and Happy Holidays,
Kagami