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4.0 coolant flush tips?

BrunoPizz97

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Jul 11, 2019
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I am going to be doing a coolant & heater core flush on my 97 wrangler because I noticed whenever I start my car in the morning to warm up a bit it always goes past 210 degrees but never in the red. As soon as I drive it cools down back to normal temps, and also my heater used to blow hot air not its cold/ luke warm sometimes hot. So with that said does any one have any tips to flushing this thing out good? I saw people post that using tap water is ok some people say use distilled because tap has minerals and can rot the radiator or block. Someone clarify this. Also should I use ZEREX G-05 50/50 mix or should I use the concentrate and dilute it myself, others say that there is still water in the lines so its not going to be a 50/50 more like a 70/30 or 60/40, so some insight on this would be greatly appreciated.
getting this done next week before it begins to get into the freezing temps here in NY.
 

jazngab

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Drain the radiator and engine block. Flush the entire system, including the heater core. I used distilled water myself. I would buy the Zerex G05 and dilute it 50/50 myself. You might want to make sure your cooling system components are all good too.
 
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Steel City 06

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Make sure whatever final flush you do is with distilled water. The first flush can be tap water, but distilled is preferable. I recommend using a chemical descaler available at any auto parts store. Drain the coolant, refill with water and flush per the directions on the bottle, and let the engine warm up. Just keep an eye on the fluid level in the radiator. Too much of an air gap, and the water won't flow and could boil inside the engine block. Once it's idled for a while, go for an Italian tuneup. The goal is to get the flush mix as hot as possible and moving as fast as possible. (If you have a big hill on a freeway nearby, climb it as fast as possible, ideally near redline and floored.)

Just be prepared that descaler can reveal problems, like radiator, heater core, or even head gasket leaks. It won't cause them, but it may unclog previously clogged leaks. Personally, I see this as a good thing. Better to uncover a bad gasket or radiator at home rather than hundreds of miles away on the freeway.

Buy the concentrate and mix it yourself with distilled (or deionized) water. You can mix it a bit stronger to counteract the remaining water in the block.

This is also a good time to replace any cooling components you suspect, like radiator, hoses, water pump, thermostat, etc. Also a good time to install a block heater if you live somewhere cold.
 

tworley

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If it runs hot at idle, but cools once driving that is pretty indicative of a failing fan clutch.

I would go ahead and flush the entire system and use zerex g05 as mentioned. Distilled water is less than a dollar a gallon at walmart. You could mix it yourself so you know it is a true 50/50 mix. Though, if you flush the block with a hose (tap water), know that you will have roughly a gallon of that tap water in the block. Adjust accordingly.
 
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TJ4Jim

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Make sure whatever final flush you do is with distilled water. The first flush can be tap water, but distilled is preferable. I recommend using a chemical descaler available at any auto parts store. Drain the coolant, refill with water and flush per the directions on the bottle, and let the engine warm up. Just keep an eye on the fluid level in the radiator. Too much of an air gap, and the water won't flow and could boil inside the engine block. Once it's idled for a while, go for an Italian tuneup. The goal is to get the flush mix as hot as possible and moving as fast as possible. (If you have a big hill on a freeway nearby, climb it as fast as possible, ideally near redline and floored.)

Just be prepared that descaler can reveal problems, like radiator, heater core, or even head gasket leaks. It won't cause them, but it may unclog previously clogged leaks. Personally, I see this as a good thing. Better to uncover a bad gasket or radiator at home rather than hundreds of miles away on the freeway.

Buy the concentrate and mix it yourself with distilled (or deionized) water. You can mix it a bit stronger to counteract the remaining water in the block.

This is also a good time to replace any cooling components you suspect, like radiator, hoses, water pump, thermostat, etc. Also a good time to install a block heater if you live somewhere cold.
Everything you stated makes perfect sense up to the deionized water which is the last thing you want in contact with steel or cast iron. I have installed deionized water systems in blood labs and the only material suitable for delivery is plastic pipe or true stainless steel. The deionized water contains no minerals and it's the nature of water to self correct it's own chemical imbalance and it will find a nice supply of iron in the block to satisfy it's needs.
 
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Goatman

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Flush with normal tap water is perfectly safe and normal. Take it to a shop and they will flush with tap water also.
After you flush the system swap the heater hoses around. Put the in hose to the out side and the out hose to the in side. This will flush the heater core from both directions doing a much better job of getting any crud out of it. Use a descaler if you want to.
Then swap the hoses back so they are in the normal position. After all that has been completely flushed and drained be sure to flush once more with distilled water. Drain that all out.
I prefer to use straight coolant and mix with distilled water as opposed to buying the premixed stuff. You are paying the same money per gallon while getting only half the product.
If you have any old hoses I'd replace them after the flush, before the mix fill. Any questionable clamps too.
Be sure all this is done in a way that will make sure your pets can't get to any of the fluid. Antifreeze is very tasty to animals, but also highly toxic. And the pain they will be in is extremely difficult.
Be sure to recycle the original antifreeze mix you drain out.