Rust in coolant system... which is the RIGHT way to flush the system? SBC 350

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95 Chevy G20 Van, 98k miles. SBC 350 5.7L. Recently bought from a third party seller. There's a rusty residue all along the coolant system. My first thought is that someone mixed dex-cool with regular green. Top of the radiator, inside of the heater core valve and thermostat house all look "rust stained". I didn't notice any sludge deposits or anything, it just seemed stained. Can't wipe it off or anything but no signed of deposits at least from the parts I replaced. i can't tell if this is the "sludge" they talk about with dex-cool and regular green mix: [Linked Image] I'm assuming no ones ever changed the coolant, not for a long time at least, and it's just gotten rusty from sitting. If it looks like the dex-cool was mixed with green let me know. Either way,I want to flush it and get everything out and I've heard of so many different ways to do it, just hoping for some clarification on what has worked best for people. I've heard:
  • Flush with straight water with a hose
  • 50/50 water and white vinger mix
  • fprestone radiator flush and water
  • cup of cascade dishwasher detergent, + water
  • caustic soda + water
Which one is the best option for my issue? Or at least, which will likely be effective and won't damage my system? Anything I should look out for when flushing? Assuming I need to flush from the radiator as well as the block. Haven't done a coolant flush in a while and the last flush I did was on a 325i... any help appreciated.
 
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I would so the dishwasher detergent flush followed by a citric acid flush. That should clean everything out. Obviously do it with no t-stat in the system and maybe consider new hoses when its all over.
 
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Originally Posted by bdcardinal
I would so the dishwasher detergent flush followed by a citric acid flush. That should clean everything out. Obviously do it with no t-stat in the system and maybe consider new hoses when its all over.
So use the Prestone it's a sodium citrate solution.
 
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Water! The dish soap is if you get oil in the system from a head gasket failure. It's got chlorine in it so it's pretty corrosive. The citric is if you get lime in the system from mineral-heavy water. Leave the thermostat in, drain the system, refill with decent water. Not limey tap water but if it tastes ok I'd run it. Drive to work. Drive home. Cool, drain and repeat all week. Use distilled for the last water cycle if it excites you, then drain, then fill 1/2 total capacity with 100% dexcool and top with water.
 
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I'd do several distilled water flushes. Make sure you turn the heater to max hot. Does your car call for Dexcool? If it does, I'd mix it 50:50 before adding. I'd then run the Dexcool for a week or so and drain and refill with fresh 50:50 Dexcool:Distilled water. Then sleep easy.
 
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That is not a dexcool disaster. Once rust starts it wont ever stop. Just like a rusty car in detroit. You can only slow it down. That mess is caused by running straight water or letting antifreeze go too long. The bottom of the water jackets are full of rust chunks. The water pump is much higher so draining it there will not get the chunks out. You must remove the drain plugs or a freeze plug on each side to flush the water jackets out.
 
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jac962

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Thanks for all the help. As I suspected I'm getting mixed answers here. Sounds like most people are saying flush with water, backflush with water, lots and lots of water. I'll try that first and do the last flush with distilled and fill with 50/50. If it still seems to be gunked up I'll try the prestone and then if all else fails resort to another method. Thanks again.
 

jac962

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Originally Posted by Chris142
That is not a dexcool disaster. Once rust starts it wont ever stop. Just like a rusty car in detroit. You can only slow it down. That mess is caused by running straight water or letting antifreeze go too long. The bottom of the water jackets are full of rust chunks. The water pump is much higher so draining it there will not get the chunks out. You must remove the drain plugs or a freeze plug on each side to flush the water jackets out.
Are you talking about the drain plug bolt in the block, or the freeze caps? I believe there's an actual bolt that can drain the block do I have to remove the freeze plugs too? Can't imagine it's much fun trying to get those out.
 
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Originally Posted by jac962
Originally Posted by Chris142
That is not a dexcool disaster. Once rust starts it wont ever stop. Just like a rusty car in detroit. You can only slow it down. That mess is caused by running straight water or letting antifreeze go too long. The bottom of the water jackets are full of rust chunks. The water pump is much higher so draining it there will not get the chunks out. You must remove the drain plugs or a freeze plug on each side to flush the water jackets out.
Are you talking about the drain plug bolt in the block, or the freeze caps? I believe there's an actual bolt that can drain the block do I have to remove the freeze plugs too? Can't imagine it's much fun trying to get those out.
Either. Which ones you can get out. Often the block drains are not acessable in the car. Easier to knock a freeze plug out. If you dont you wont ever get it clean.
 
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Originally Posted by jac962
Originally Posted by Chris142
That is not a dexcool disaster. Once rust starts it wont ever stop. Just like a rusty car in detroit. You can only slow it down. That mess is caused by running straight water or letting antifreeze go too long. The bottom of the water jackets are full of rust chunks. The water pump is much higher so draining it there will not get the chunks out. You must remove the drain plugs or a freeze plug on each side to flush the water jackets out.
Are you talking about the drain plug bolt in the block, or the freeze caps? I believe there's an actual bolt that can drain the block do I have to remove the freeze plugs too? Can't imagine it's much fun trying to get those out.
One side will have a Knock Sensor in the block drain hole (7/8"/22mm) & the other side will be a 9/16" headed steel 1/4" pipe plug. Using a 1/2" drive impact with 9/16" wobble socket is the best way to remove the pipe plug, Replace with Brass!! The odds of ruining the Knock Sensor is pretty high if original.
 
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"cup of cascade dishwasher detergent, + water" Not this, they removed the phosphates decades ago for environmental reasons. It no longer has a high enough acid content to be effective in your cooling system.
 
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On old brass/copper radiator cars, I still use oxalic acid and washing soda neutralizer. On a rig with an aluminum radiator, I normally don't use anything and just back flush with a LOT of water. If that doesn't cut it, a quarter cup of citric acid powder per gallon works a lot better than the Prestone cleaner. Just don't leave it in there too long. If a fellow would just drain and fill the radiator with a 50/50 mix once a year or so you don't gotta worry about flushing at all.
 
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I had a 1995 Chevy Tahoe 4x4 not too long ago, and it had rusty coolant when I got it. I bought one of those Prestone Fush-N-Fill kits from WalMart that you install in the heater hose, and then hooked up the garden hose to that kit and just ran the engine with the radiator plug open. Some nasty stuff came out for a while. After about 10-15 mins the water was crystal clear, so I closed the drain plug, closed the opening on the Prestone kit, and refilled with Green universal coolant. Had that truck for year after that and truck ran perfect, and green coolant stayed green and fresh looking. No complaints from truck's new owner either.
 
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Originally Posted by Vladiator
I had a 1995 Chevy Tahoe 4x4 not too long ago, and it had rusty coolant when I got it. I bought one of those Prestone Fush-N-Fill kits from WalMart that you install in the heater hose, and then hooked up the garden hose to that kit and just ran the engine with the radiator plug open. Some nasty stuff came out for a while. After about 10-15 mins the water was crystal clear, so I closed the drain plug, closed the opening on the Prestone kit, and refilled with Green universal coolant. Had that truck for year after that and truck ran perfect, and green coolant stayed green and fresh looking. No complaints from truck's new owner either.
+1 Use one of these kits to get it as clean as you can, then install a coolant filtration system. It's the only way you will keep the system clean once the rust starts.
 

jac962

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Thanks for all the help guys. I'm going to get going on in tomorrow. Hit the block drain plugs with some PB blaster tonight and hopefully by morning I won't have to torch them to get them loose..
 
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