A month ago, I was getting cold start misfires on Cylinder 4. I did a manifold and EGR clean out 9 months ago but checked again and it’s not clogged. I changed the plugs (also did this 9 months ago) again with the good ones and still had misfires so I changed the coils. No problems for 2-3 weeks. Now I’ve been getting very intermittent misfires on Cyl 1, but this time they happen when the motor is warmed up, but at low throttle. I guessed I may have gotten one bad plug and I even tested the coil by moving it to cylinder 2. The misfires stayed on 1, so I changed the plug. Still a few misfires on cylinder 1. So infrequent, it doesn’t really throw a code, it just gives a brief death rattle, and I look at the non-live data at the misfire counts to identify cylinder 1. I checked my coolant and it is low….. uh oh, sounds like a head gasket. So I’ve been trying to decide between a JDM gen 3 or gen 4 motor swap and realized I need confirmation before I get so deep in a project. So I got the combustion gas tester and tested it 4 times, in a cold motor, in a hot motor turned off, in maintenance mode at idle, and revving the motor a bit then while in maintenance mode. The blue liquid doesn’t even really turn green! Even after 2 minutes of testing. It does turn a lighter blue. 1. Does compression testing even work? My Prius does consume oil, about a quart every third tank of gas, so won’t the rings be stuck and fail compression even if the HG is intact? 2. Should I borescope it and add compression the the cooling system? Or is the leak probably too small to catch this? 3. should I just top off the coolant and drive it till the misfires are consistent? Note, I don’t think I’ve ever changed the coolant. It has always been a clear pink color and I never lost a drop until I spilled some during the egr clean out. I should probably change it all out either way. 4. What other ways should I test it? I realize HG failure is basically inevitable and I have a 2012 Prius four with 260k miles. I am the original owner. All OEM parts (denso/ngk coils/plugs). I am not a pro mechanic but not afraid of big projects, but I don’t want to spend $2k on a JDM 4th gen and do the swap out frankenprius labor until it for sure needs it. Oh by the way a month ago I did change out fuel injectors with Rock Auto remanufactured OEM injectors. Thanks for any help or suggestions.