About a month later my low coolant warning came on, but I was just above the minimum line and to this day, no matter how far up I fill the reservoir after 1-2 weeks it goes to right around the minimum line and my low coolant warning comes back on. As bad as it sounds I went about 5 months without filling the coolant on a low coolant warning because it never overheated. Weird thing is the pressure will release when the cap is unscrewed after sitting even for a few days.
The misfire has increased in how often it happens to most of the time on cold start but still rarely is worse the 3 seconds. I have only gotten a check engine light 1-3 times. The misfire seems to be typically only one cylinder but the car has reported misfires on both cylinders 1 and 3. Misfire sometimes also still happens after sitting for only 1-3 hours. Temperature, weather, coolant level, how I drive, and time since parked don’t seem to affect the misfire in any way either.
During the past 8 months here is what I have determined that makes me think it might NOT be a cracked block:
1. Both the old sparkplugs and recently replaced all appear to be burning well, sparkplugs don’t look different from one cylinder to the next and none have a tint to them like or are exceptionally clean to suggest burning coolant. Using a borescope, there’s also a seemingly normal amount of carbon buildup on the tops of the pistons. There were no obvious cracks in the cylinder wall, but honestly the scope didn’t really have good enough resolution to see a small crack if present.
2. Car passed combustion gas test on the cooling system (Did discover through this test though that their was air in coolant tank which hopefully has been fully removed) I did this about 2 months ago.
3. Pressure test on both coolant reservoir found a small leak in the overflow hose, but after fixing that, it held pressure for at least 15 minutes and the pressure cap released at the correct pressure.
4. No liquids in areas they shouldn’t be (no oil in coolant or signs of coolant in the oil on the dipstick or during oil change) also haven’t looked super hard but can’t find any obvious dried coolant on anything.
5. ONLY misfires at startup after it’s been sitting for at least a couple hours, never once had it start running funny at idle or while driving no matter the RPMs.
6. There’s no obvious sign of a leaking heater core (sweet odor with heat, puddling on the carpet or thick film on the inside of the windshield).
7. Just before writing this I did another combustion gas test from cold start to see if it would fail during the misfire and it passed although the test does recommend doing it at running temperature but I’m not sure how that would effect it.
I plan on doing a fuel pressure test on the fuel rail too to confirm my injectors are working properly and not dropping fuel pressure too quickly. About the only other things I can think of doing is checking the water pump and doing a cylinder leak-down test. I haven’t been daring enough to try to take the head off to check for cracks in the cylinder walls. I can live with the misfire but I don’t enjoy being scared of driving long distances and always having extra coolant in my car because of the low coolant every 100ish miles after filling the tank. If anyone has any ideas of what could be causing this it would be greatly appreciated, I want to get back to enjoying this car as much as I did before these issues.