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Old 05-29-2011, 04:50 PM   #1
Howard
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Default Best way to flush coolant?

Any tips?

I've heard that draining the radiator will not release all the coolant in the system. If this is the case, then obviously filling with water and draining again (and repeating) will do a pretty good job of circulating the old coolant out if the engine is on and hot. However, do you have to measure how much comes out at the end to figure out how much antifreeze goes in, since the system might never be empty?
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Old 05-29-2011, 05:02 PM   #2
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you dont have to measure how much comes out. Coolant is full when all the air pockets are out of the system. This doesn't need to be exact at all. As long as the radaitor is full and your overfill tank is near max you good to go.

The drain in the bottom of the radiator only drains that. There is about 1/2 left inside your engine. There are freeze plugs on the block you can remove and have it come out, or just put water in it.

I do mines often that i normally just do a radiator drain and fill.
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Old 05-29-2011, 05:04 PM   #3
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draining the radiator will get rid of the coolant in the radiator, for most cars that is 75% of the coolant, the rest is in the block. You can do a quick change by changing the radiator stuff, if not you got to drain, fill with distilled water, drain again. Or you can remove the lower radiator pipe and let the stuff drain from the block.
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Old 05-29-2011, 06:03 PM   #4
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Howard, after you flush and are ready to refill, add straight antifreeze - not premixed, based on 1/2 of the capacity of the cooling system. The capacity will be listed in the owners manual. Top off the remainder with water and you should be good to go. Yes there will be water left in the block, the heater core (remember to have the heat on when you flush) and hoses but there should be enough room to add the proper amount of AF for a 50/50 mix.

Be sure to run until the thermostat opens, shut off and let it cool and add more water as required to ensure the system is really full. If there are air bleeds at high points you will want to crack them to let all the air out. This is very important.

An old trick is to rev the motor up and hold it a relatively high RPM while you top off the radiator and quickly put the radiator cap on. It's easier with two people. When doing so, you will see the coolant level drop as the suction of the water pump pulls coolant from the radiator. Also, your car may have a surge tank that is the highest point of the cooling system. The radiator may still have a cap, but that is not the place to add coolant.

It's also a great time to replace hoses, radiator caps, surge tank caps and thermostats. Routine maintenance and all that jazz.
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Old 05-29-2011, 06:29 PM   #5
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Another simple process is to take the upper radiator hose off (at the top radiator connection) and remove the radiator cap put your garden hose in and turn the water on but not full blast just enough to have it running over pretty good... Then start the engine and let it run and warm up to the point that it will discharge all of the coolant in the block and when the water coming out of the top radiator hose is clear its fully flushed... Then shut it off and remove the lower radiator hose and drain the system (be careful though the water will be quite hot)...

One other note since your using a city water supply to do this and will have fairly nasty water in the block then just use a product called (Wixcool) which is of course made by Wix... It will neutralize the crap in the city water and put extra corrosion inhibitors in the cooling system... It was originaly made for diesel engines but works excellent in most any cooling system that uses either green or universal coolant... Not sure about Dexcool though...?

I would go with the 50/50 premix coolant which makes it simple or add 1 gallon coolant then 1 gallon water then in 1/2 gallon increments...
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Old 05-29-2011, 06:57 PM   #6
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the problem with flushing it with a hose is that you're going to leave water behind, diluting your coolant mix. same with refilling with water. either just do a normal drain and fill and accept that maybe 20-40% has been left behind (depending on cooling system design), or do the drain twice thing, but use mixed coolant instead of just water (yeah, it gets wasted, but it's not that expensive esp if you're using generic green coolant).

my rec- if the manufacturer says do coolant every 100k and you don't want to pay for someone to use a flush machine on it (some shops lie and just do drain and fills, anyway), then just do a normal drain and fill every 50 and you should be more than fine.

edit: if the pressure cap is on the radiator, you'll want one of these.

http://www.summitracing.com/parts/LIL-24610

if you have an overflow with a pressure cap (should also have more than one hose going to it), the tank serves the same purpose and the funnel kit is not needed. well, technically, it's never 'needed'; but if it's got a traditional rad cap and you try and bleed without one, you're gonna have to babysit the car and make a huge fuckin' mess.

Last edited by brblx; 05-29-2011 at 07:00 PM.
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Old 05-29-2011, 07:12 PM   #7
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Good luck Howard, there's no consensus here whatsoever...
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Old 05-29-2011, 07:23 PM   #8
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Quote:
Originally Posted by brblx View Post
the problem with flushing it with a hose is that you're going to leave water behind, diluting your coolant mix. same with refilling with water. either just do a normal drain and fill and accept that maybe 20-40% has been left behind (depending on cooling system design), or do the drain twice thing, but use mixed coolant instead of just water (yeah, it gets wasted, but it's not that expensive esp if you're using generic green coolant).

my rec- if the manufacturer says do coolant every 100k and you don't want to pay for someone to use a flush machine on it (some shops lie and just do drain and fills, anyway), then just do a normal drain and fill every 50 and you should be more than fine.

edit: if the pressure cap is on the radiator, you'll want one of these.

http://www.summitracing.com/parts/LIL-24610

if you have an overflow with a pressure cap (should also have more than one hose going to it), the tank serves the same purpose and the funnel kit is not needed. well, technically, it's never 'needed'; but if it's got a traditional rad cap and you try and bleed without one, you're gonna have to babysit the car and make a huge fuckin' mess.
Wait, so if my overflow tank doesn't have a pressure cap on it then I shouldn't be filling into it?
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Old 05-29-2011, 08:10 PM   #9
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If you are going to flush it, do so with distilled water.

In reality, this is one of the better jobs to spend the $50-75 at a quick lube to have them do. There is a ton of waste water and none of it should be allowed to go into the ground. I believe in all places in the US you can just flush coolant in a toilet or household drain (not storm drain)...water treatment removes it.

Even if there is some residual water doing it yourself, it won't affect anything enough to matter. When you get a power flush you will know only 'new' water will be left behind.
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Old 05-29-2011, 08:11 PM   #10
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Quote:
Originally Posted by Howard View Post
Wait, so if my overflow tank doesn't have a pressure cap on it then I shouldn't be filling into it?
no. you fill the radiator. generally when i drain coolant, i fill the system (with an airlift, ideally (i'd link you but they're expensive and not absolutely needed)), let it bleed with a generic funnel adapter (you'll want that), then dump the extra out of the funnel into the overflow to get it around the full mark.

tanks with a pressure rated cap are actually in the cooling system loop, and are typically the the high point, so you can fill the coolant there and they generally bleed air pretty efficiently on their own. the ones with a flimsy one piece plastic cap are just an expansion tank- if the cooling system builds too much pressure, the excess coolant gets pushed into it. it is no so good at bringing coolant back in. if you try and fill your radiator though the overflow, it's never gonna happen.
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Old 05-29-2011, 08:13 PM   #11
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Quote:
Originally Posted by Howard View Post
Wait, so if my overflow tank doesn't have a pressure cap on it then I shouldn't be filling into it?
Ok the real first question... What auto is this...? Even with a plastic reservior type tank the cap is pressure rated, this is what most newer cars have... An overflow tank is whats used with a radiator with a cap on it and is of course used on older cars...

Also with the method I indicated the amount of water in the block is marginal and anything over a 30% solution is fine it does not have to be 50/50 unless your in a very cold area and if so then simply adjust with straight coolant to get the mix to the ratio you want... Just have an antifreeze tester handy after the car has been ran enought to mix the solution... Uh not rocket science...
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Old 05-29-2011, 08:26 PM   #12
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If memory serves the recommended flush procedure for a Miata(ish) is to:

-open radiator cap
-drain coolant out and properly discard
-stick a garden hose in the top of the radiator
-leave the drain open, the garden hose should flow more than the drain can... drain
-start and idle the car with the hose going and the drain open
-water will get everywhere, but fresh water will be cycled through the engine and all the goop will get flushed out
-stop the car
-drain the water out of the car
-close drain
-refill with coolant/distilled water
-start and run car until thermostat opens
-refill coolant as bubbles come out
-stop car and let it cool
-refill coolant again
-close radiator cap
-good to go
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Old 05-29-2011, 09:16 PM   #13
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Quote:
Originally Posted by Bartman39 View Post
Ok the real first question... What auto is this...? Even with a plastic reservior type tank the cap is pressure rated, this is what most newer cars have... An overflow tank is whats used with a radiator with a cap on it and is of course used on older cars...

Also with the method I indicated the amount of water in the block is marginal and anything over a 30% solution is fine it does not have to be 50/50 unless your in a very cold area and if so then simply adjust with straight coolant to get the mix to the ratio you want... Just have an antifreeze tester handy after the car has been ran enought to mix the solution... Uh not rocket science...
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Old 05-29-2011, 11:49 PM   #14
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Quote:
Originally Posted by JCH13 View Post
If memory serves the recommended flush procedure for a Miata(ish) is to:

-open radiator cap
-drain coolant out and properly discard
-stick a garden hose in the top of the radiator
-leave the drain open, the garden hose should flow more than the drain can... drain
-start and idle the car with the hose going and the drain open
-water will get everywhere, but fresh water will be cycled through the engine and all the goop will get flushed out
-stop the car
-drain the water out of the car
-close drain
-refill with coolant/distilled water
-start and run car until thermostat opens
-refill coolant as bubbles come out
-stop car and let it cool
-refill coolant again
-close radiator cap
-good to go
uh, hose water isnt distilled, I would be scared about the minerals in there
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Old 05-29-2011, 11:54 PM   #15
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uh, hose water isnt distilled, I would be scared about the minerals in there
The minerals in city water will stay solubilised - it takes time for scale to build up. Once drained, the minerals will mostly go away.
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Old 05-29-2011, 11:57 PM   #16
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uh, hose water isnt distilled, I would be scared about the minerals in there
gotta play dualing banjos and be working on a 1975 Ford Pickup to understand.
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Old 05-30-2011, 12:00 AM   #17
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No one has mentioned the aspirin trick?

Here goes. Drain the radiator. Disconnect the hose with contains the t-stat and remove it, replace hose. Start the car and run it for about a minute. The car should be cool before doing this (sitting over night). Without the t-stat in place the water pump will circulate the remaining coolant into the radiator/reservoir in about a minute - no, the car won't overheat or be damaged.

Now, take an aspirin and place it inside the t-stat, essentially propping it open, replace the t-stat. Fill the radiator and start the car. The water pump will start circulating coolant immediately, continue to fill the radiator until it's full. This ensures a complete fill. After about five minutes the aspirin in the t-stat will dissolve and it will close, returning the coolant cycle to normal operation.

Good luck.

Do not run your car for more than a minute without coolant. You have been warned.

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Old 05-30-2011, 12:05 AM   #18
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The water pump doesn't suffer any damage from running dry?

At what point do you close off the drain?
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Old 05-30-2011, 12:12 AM   #19
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Water isn't a lubricant so the water pump doesn't care if it's moving water or air. The water does dissipate heat though, air, not so much, so you don't want to do this for long, my rule is a minute.

I typically leave the drain plug out for an hour or so as it will continue to drip, drip, drip for quite a while. Every car is different though.
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Old 05-30-2011, 12:26 AM   #20
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I'm surprised nobody mentioned (unless I missed it) to check on your specific engine in regard to any concern of coolant air locking. It is well and good to drain the block completely, but only if you are certain there is low risk of air locking. Some of these newer engines are notorious for that and have addition plugs you can remove to prevent that from happening. Some parts of the cooling system can stay air locked for a long, long time... too much time, and you may cause damage.

Please double check a service manual for that specific car/motor for any special procedures.
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Old 05-30-2011, 05:53 AM   #21
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Quote:
Originally Posted by Howard View Post
The minerals in city water will stay solubilised - it takes time for scale to build up. Once drained, the minerals will mostly go away.
Exactly.

Quote:
Originally Posted by Howard View Post
The water pump doesn't suffer any damage from running dry?

At what point do you close off the drain?
Quote:
Originally Posted by Vic Vega View Post
Water isn't a lubricant so the water pump doesn't care if it's moving water or air. The water does dissipate heat though, air, not so much, so you don't want to do this for long, my rule is a minute.

I typically leave the drain plug out for an hour or so as it will continue to drip, drip, drip for quite a while. Every car is different though.
The water pump will suffer damage running dry, or at least I'd be scared that it would. Water isn't a great lubricant, but it helps a lot, and the coolant itself is a good lubricant. Ever get some coolant or pre-mix on your fingers? It feels really slippery.
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Old 05-30-2011, 05:55 AM   #22
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uh, hose water isnt distilled, I would be scared about the minerals in there
If you're worried about it the last flush step can be done with a few gallons of distilled water, that will ensure that the last little bit of tap water is gone.
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Old 05-30-2011, 05:57 AM   #23
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Unless there is oil or other gunk in your cooling system you are over thinking it.

Drain coolant from drain on Rad. Remove lowwer Rad hose to get the rest. After that reinstall hose and drain. Then top off with a 50/50 mix.

Good time to also install a new Therostat and Rad/Pressure cap.
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Old 05-30-2011, 09:22 AM   #24
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I never flush, always just drain and fill.
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Old 05-30-2011, 01:48 PM   #25
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Wow, some people think those jiffy lube types of places use distilled water? Surrrrrrrrre they do.

And, while many mentioned that during a flush, some of the water remains behind in the block, yet not one person has mentioned the little bulb thing that sucks up some of the fluid to test for the correct mix (antifreeze tester)? Wow. They're like $2 And, it takes the guess work out of wondering how much water was left behind.
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