Last week I changed my coolant and yesterday I checked it's strength using one of those cheap, floating *****, testers. It is reading low (-10 degrees protection as opposed to -20 before the change).
This was my first time changing coolant in a vehicle with a degas reservoir.
I drained the radiator and the two block drains. Then filled with tap water and chemical flush. Ran it for 15 minutes. Drained the radiator and block again. Filled again with tap water and let run 15 minutes. Drained radiator and block again. Then filled with 50/50 distilled water and antifreeze.
I was able to get in only about 14 quarts of mixed coolant. I think the system is supposed to hold about 20 total.
Did I do something wrong and not get all the tap water out before putting in the new coolant?
Is it possible the tester I used is inacurate?
This a 2001 F-150 with 105K miles that has had regular coolant changes per Ford schedule.

 

Could be you answered your own question.

 

Only problem I see is you used 50/50 mix when 60/40 Coolant/water was probably a better choice. I always add more coolant than water because there is still some water in the system from the flush. I still wouldn't worry about it though.

 

"Then filled with 50/50 distilled water and antifreeze.
I was able to get in only about 14 quarts of mixed coolant. I think the system is supposed to hold about 20 total. "

You answered you own question. If you know your cooling system holds 20 quarts total (using data from your owner's manual) then 50/50 mix of 14 quarts will get you only 7 quarts of coolant, that's only 35% coolant mix, not 50/50. You still had water in the system before you added the mix.

 

I just flushed mine today. I first added straight anti-freeze and then the 50/50 mix after that. I'll give it a week to fully circulate and burp any air out and check it then.

 

invest in a Monometer!!!
50/50 mix is good
once you get above 73 precent antifreeze you start loosing cooling abilities

 

Yeah, you need to put in the proper amount of straight antifreeze first, then fill with water. It's almost impossible to get all the water out, so if you add 50/50 antifreeze you'll end up with something more dilute.