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Discussion Starter · #1 ·
I have a 2006 GC with 3.8. It has a rear heater. I plan to put in a new radiator next weekend. Before I do that, I plan to run Prestone Flush and Cleaner for one day (about a 10 hours, I am a delivery guy) on Friday before the work. Mainly for the front heater core. Seems it took longer than it should have to warm up this past winter. So I will run that, then the weekend, I will drain the radiator, then refill with distilled water and run for several minutes, then drain again. Then I will replace the upper and lower hoses and the radiator. My question is do I have to be concerned about this flush not draining sufficiently from the entire system? How will I get a proper 50/50 mix if I don't know if the system is actually drained? Do you have to check your fluid after it is mostly filled with a gauge instead of relying on a 50/50 mix?
 

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It can be tough to completely drain and refill these systems, but you do have options. You could pull your wiper cowl and disconnect heater core hoses and carefully blow out the heater cores with compressed air & an appropriate nozzle. As far as concentration goes, you can fill with 50/50 and just wait for the air to bleed out after first start. Test your coolant with a specific gravity tester to make sure it's good for -40°. Then add straight coolant or water if/as needed to correct concentration. If it's at the right concentration, then just keep topping up with the 50/50 mix. These vans are great at trapping air, so I'd encourage you to have the front end elevated and expect it to burp up some air pockets a couple times. Make sure you reconnect all the heater core hoses to all the right nipples. As an option, you could leave hose clamps loose on the heater core hoses and disconnect one at a time before the engine gets warm and pull the hoses just long enough to get coolant flowing and push out some of that air. Do make sure you put all the clamps back on when you're done and pay attention to how hot everythings starting to feel. I'm not taking responsibility if you burn yourself.
 

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Discussion Starter · #3 ·
Thx for that info common. I do know how to take off the wiper cowl. I do that every 75k when I do plugs. I put on 45k a year with my job, so I have done it many times. I have had about 7 GC/T&C so far. All '05 or '06. But as far as what you suggested, would a distilled water flush suffice (for flushing the Prestone Flush effectively) even if some distilled water remains in the cores? Then after I put in the new radiator and hoses, fill with a slightly higher concentrate, checking with a gravity gauge as it fills and burbs?
 

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A little distilled water left in the cores will be fine. Won't make that much of a difference. If you do have gravity specific tester you can use that to judge how close the mix ratio is. Anything reading close to 50/50 is good. Distilled water is much preferred to tap water.
 

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I've never bothered with chemical additive flushes, so I don't know what to say about flushing/diluting your Prestone stuff. There's bound to be some residual amount of the flush chemical no matter what you do. It is why I encouraged you to blow out the heater cores with air pressure so you could minimize your concerns in the first place. You don't have to account for concentration of water or Prestone if neither is even in the system anymore. Trying to start by adding more concentrated coolant first is a guessing game. I'd rather you just start with 50/50 and then correct if it's far enough off. This will give yourself a baseline to adjust from. Doug has made a good point in that it only needs to be close. Most coolant testers aren't that overwhelmingly precise in the first place. That should be more than enough for you to make a decision and move forward. Good luck!
 

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Discussion Starter · #6 ·
I think I will flush it twice with distilled water. Then after re-assembly/refill, I will check with gravity gauge. Blowing out the lines sounds awesome, but I don't feel like taking that much apart.
 

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FWIW - long ago I used Prestone SuperFlush to flush out the heater core of a '93 Ford Aerostar. I flushed the entire system and refilled with 50/50 coolant mix and never had a problem. I'm sure there was some residual SuperFlush left, but it was negligible. Interestingly thing was the heater core was relatively easy to get to if needed - remove glove box, remove 4 bolts on the access panel and the heater core was right there.
 

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Discussion Starter · #8 ·
It is apparently a 16 qt capacity. Flushing twice. Why not just pour in 2 gallons concentrated. Perhaps a 1/2 gallon distilled water between the 2 gallons to help it mix a tad, then top off with distilled water? Of course checking after running it for 10 or 15 min. Of course, not forgetting the overflow res. I wonder if that is part of the overall capacity.
 
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