I have a 2015 fusion 1.5 ecoboost. I replaced the motor 300 Miles ago with a new block and head along with other new parts. Shortly after I noticed coolant loss, and realised the charge air cooler in the intake was cracked and leaking coolant. Fixed that! Then it appeared the coolant level was dropping and rising (Im aware of expansion of the coolant) I bought a head gasket co2 leak test test and it doesnt show any signs of a leak, I havent noticed any exhaust since what I assume was the residual from the intake burnt off. Should I worry or just keep an eye on the coolant? Could it be air in the cooling system? Expecting the worse but hoping for the best. Worse case in another 100 miles I will be checking valve clearance so I could "easily" replace the head gsaket at that point.
New engine after just 6 years? Holy guacamole! Anyhow, a pressure test will usually find coolant leaks pretty quickly. If you're lucky it's just a loose clamp or a pinhole leak in a hose. (Amazon link many not work, it's for a Mityvac MV4560 Automotive Radiator/Cooling System Pressure Test Kit.)
https://www.amazon.com/Mityvac-MV4560-Radiator-Cooling-Pressure/dp/B003V9L05G
Yes. The original ecoboost engine turned out to be trash. A defective water jacket that they had to revise. No recalls but my local dealer has sold 18 short blocks in 6 months. I have access to a pressure testing kit but none of the caps fit exactly right. Ones close but you have to keep pressure on it with your hand or it pops.
Is the coolant rising and falling as the engine is running? If so, there could be air in the system. The cooling system can somewhat bleed itself as you drive, high RPMs on the water pump will eventually force coolant into the heater core, but it won't readily come out like it should, hence the level drops. The heater core is the highest part of the system, if there's air in there, you're low on coolant. Turn the heat on in the car, if it's hot, then there may not be any air in the system. If it isn't, that's a good sign you didn't fully bleed it.
if the heat is working, you can put leak dye for cooling systems in the radiator, top it off and drive around for a bit. Let it cool, then check for leaks. Unless it's burning the coolant, the dye should show where it's losing coolant from.
Another thing you can do is pull the spark plugs. If one or more look like it's been steam cleaned, or is noticeably cleaner than the others, that would be an indicator of a blown head gasket as well.
The heat works without a doubt lol. I havent noticed it rising or dropping while running. Ive just been keep an eye on it before every drive. The last drive it looked a hair low so I topped it off and after the drive it had risen quite a bit. More than the usual minimum, maximum amount. Maybe I am just looking at it too much and not aware if how a normal system fluctuates? The next step would be as you suggested and maybe run a camera inside the cylinder. As stated tho I have ran a leak detection test on the head gasket numerous times now and it shows nothing, no white smoke, nothing showing signs other than funky coolant levels. I appreciate your input tho and Ill post an update if I figure it out.