I have a new (to me) car that it appears hasn't had a coolant fluid change ever, now with 120k miles. It is an 04 Corolla.
I am planning on flushing the system with distilled water a few times. But it seems to me that if I add a 50/50 mix of fluid back after the last drain, all the water left in the heater core will dilute the 50/50 mixture even more.
So since they say about half the liquid remains in the heater core after a drain, that I should add undiluted pure antifreeze to the system. That way it will mix with roughly half the water in the engine with the pure coolant I put in.
Does this sound correct? Am I right to add 100% coolant to my system after a 3 or 4 flushes with distilled water? Which would leave me with about a 50/50 mix (after driving a while and everything mixes).