Why pay for water? When you buy 50/50 premix, you are paying too much for the water. The cost of premix is a little less than pure coolant, but a lot more than a jug of water. Another issue is that, almost never can you get all the old water out of the engine and cooling system. So if you add something(coolant/water) it will be diluted by the water remaining in the engine. So why dilute 50/50 to less than recommended by accident?
Of course there are those on this site who say "If you can't afford the maintenance, don't buy the Lincoln." humbug
Anyway, I am cheap. I buy pure coolant and a little less than what on paper you need of distilled water. Of course I am REALLY cheap and I get my DI water free since my factory makes it by the tub full.
My method of refilling a clean cooling system is to look in the manual for how much coolant is required(Almost 12qt for 04 V8). Divide that by half and that will tell you how much pure COOLANT you need(about 6 qt) for a 50/50 mix, NOT water. Like I said above, the coolant will be diluted anyway by the remaing water. SO, I fill up the engine with the correct amount of pure coolant. Then I top up with distilled(LESS THAN 6 qt), which on every car I have ever owned was less than half of the total capacity of the cooling system, usually at least a couple quarts less.
Bleed the system of air, you will lose maybe a cup. Top up with PURE coolant as needed. Check it a few times over the next week or so and top up with pure coolant.
This method takes a tiny bit more time than the premix, but you are more likely to have the correct dilution of coolant in the system this way.
Over the miles(100K+??) you may need to add coolant to top up. Use the pure stuff since you want to increase the strength of the aging coolant in the engine. You don't want to dilute the old coolant over time.
Just my method over the past 40+ years of messing with engines. I think I read about this method in an old Car and Driver mag in the 70s.
Jim Henderson
BTW, tap water may or may not hurt the engine, all depends on the hardness and what contaminants are in it. A little city water won't usually hurt, but distilled is better. The water has to be really nasty to cause harm in the short term. Water over say about 150ppm is hard and will make deposits over time. You can test for hardness with pool or fish tank water test kits.
