Is this a good strategy?

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So I'm planning to replace my antifreeze tomorrow. The current fill is Supertech Universal Antifreeze and I don't like it since both my dad's truck and mine have a black sludge buildup on the radiator neck and cap. The photos match silicate separation. I am planning on replacing it with Pentosin A2 antifreeze since it is also compatible with our Kia Sorento.

My plan is to drain the radiator of the old fluid, add distilled water, run it for a few minutes with the heater on and drain and refill with a 70/30 mix of antifreeze and water. Is this a good strategy? I am putting 70% antifreeze because I am accounting for the extra water in the block. Will the little Supertech left inside impact the new antifreeze?
 
I'd buy an OTC flush, and flush out the system as per the instructions, with the thermostat removed. Then disconnect the hoses from the heater core and flush that out too, forward and reverse with low pressure from the garden hose. When all the flushing is done fill it with distilled water, run the engine, drain it, and fill with the proper coolant and distilled water mix. The "black sludge buildup" is why I'd do a thorough flush.

If you're OCD like I am, after the flush run it with distilled water, drain it, refill with distilled water and run it again, dump it and fill with the proper coolant and distilled water mix. That should get all the water from flushing it with the garden hose and any remaining flush out.
 
If I was doing it I would look for block drains and get out as much of the old coolant as possible. Maybe flush. Depends upon how much time you want to spend.

I would use Zerex Asian coolant.

Consider some RMI-25 to help clean.
 
If your thermostat(s) are difficult to get to, you can do multiple radiator drains, allowing the vehicle to warm up enough each time to open the thermostat for full circulation. Turn on the heater also to make sure fluid is circulated through that. It will take 4 to 6 drains to get the system close to 100% plain water.

Study Sorento forums to see if there are any special bleed procedures to eliminate air out of the system AND to determine what the total system capacity is. If you indeed have gunk in your system, you might want to try one of the safe radiator fluid flush additives. Zerek has two versions. The stronger one (I forget which one) does a better job loosening things up. I wouldn't mess with stronger cleaners unless you have a severe gunk problem.

After the last radiator drain is pretty clear, I add approximately half of the total system capacity with concentrate, top up with water, but not all the way. After a good run to mix things up, I measure the concentration and adjust with more water or antifreeze. Total system capacity can vary from the specifications for many reasons. I only use distilled water because our tap water is very hard.

This multiple drain process can take a few hours.
 
I did a multiple drain session a couple of weeks ago. My thermostat is a pain to get to (sits in mid-air between 4 different coolant hose connections) and I didn't want to open up another can of worms yet. Worse yet, this engine design has the thermostat on the opposite side of the radiator than most cars. Hence a radiator drain only dumps a gallon of coolant. I had to do 8-9 drains to get to under 10% of the old stuff remaining. Not a fan of cutting into heater hose lines with cheesy plastic fittings. The whole thing took me around 4 hours. If I had to do it again, I'd probably pre-heat the distilled water to 130-150 deg to minimize the thermal shock of adding it to the relatively hot engine.
 
Thanks guys! Guess I'll do multiple flushes with distilled water then. I'm not going to do a chemical flush because the little bit of sludge/ silicon material that I have seen has only been on the filler neck. I just did the water pump 2 weeks ago and it looked pristine.
 
Originally Posted By: doitmyself
... multiple radiator drains, allowing the vehicle to warm up enough each time to open the thermostat for full circulation. Turn on the heater also to make sure fluid is circulated through that. It will take 4 to 6 drains to get the system close to 100% plain water.

After the last radiator drain is pretty clear, I add approximately half of the total system capacity with concentrate, top up with water, but not all the way. After a good run to mix things up, I measure the concentration and adjust with more water or antifreeze. Total system capacity can vary from the specifications for many reasons. I only use distilled water because our tap water is very hard.

I do something very similar.

When it's finally running clear I'd drain and fill with distilled water and drain once more. Whatever is left in the cooling system is almost pure distilled water. At that point I'd add full strength coolant equal to half the total cooling system capacity. Then fill with distilled water. You should be at 50:50.
 
Alright, so today I did multiple drain sessions totaling up to 6 flushes. The water was a very pale green by that point so I stopped and refilled with the new coolant. I will check tomorrow to see if the correct concentration of coolant is in the system.
 
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