I took my car into get a state inspection today and in the bay next to mine there was a van getting a coolant flush. The Van had about 88K miles on it and they said it had never been flushed before.
I was amazed at how thick and black the old coolant was. I asked if there was something wrong with the vehicle that would cause that, and they told me it was pretty normal wear and tear.
The shop I was at suggested Coolant flush @ 50K and then every 30k after that.
This comes up all the time here. For a recent thread, see
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The "answer" to your question depends on what type and year vehicle you have, and what kind of coolant it uses. Currently there appear to be several different types, which may or may not be mutually compatible. It is a good policy to use the correct fluid, and replace it as necessary, if you can find out what and how often that is.
On consumer vehicles with no filters, now that cooling systems really are almost hermetically sealed, yes. What happens is small amounts of combustion gas and casting swarf invariably get in the system and stay there.
Even if you can't do a proper flush, drop a lower hose and drain out what you can and refill with the right juice. Use exactly what the manufacturer says, especially if you can't totally flush the system.
It won't hurt, but you don't need to flush the system. Just properly drain and refill. Generally if you keep an eye on the fluid mix there isn't much you should have to do but add a bit more water or antifreeze as it's needed.
My ZJ has over 120K and the coolant has been exchanged about four times. It's still nice and green.
Black coolant indicates that either the block is cracked or someone put the wrong type in there and it reacted. There are two types of antifreeze out there and they do not mix.
We went over this before. The "good stuff" from Prestone comes in a black container now. On
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want the black jug, black cap, labelled "Heavy Duty Antifreeze/Coolant".Notice that it contains "A blend of ethylene glycol and a speciallyformulated inhibitor package designed for heavy duty cooling systemapplications." Make sure that you read that, before actually buying it. Donot take the sales person's word, he will say anything. Earle
There is another method where you check the voltage at the coolant. Usually either 0.05 volts or 0.10 volts relative to ground is considered borderline. You put your voltmeter on the appropriate scale, touch the battery negative terminal with the negative probe, and stick the positive probe in the coolant. If there is appreciable voltage, then current is flowing and metal is being removed from one place (where you want it) and deposited in another place (where you don't want it). J. C. Whitney used to sell (and probably still does) a radiator cap with a "sacrificial electrode" in it. The idea is that the electrode is a reactive metal that is dissolved before the cooling system or engine metals. It is probably better to change the coolant as needed, by whatever method, than to rely on something like this.
Of course, chemical companies don't really want you to know when it is time to change the fluid, any more than they want you to get maximum use out of your motor oil. They are happy with once every two years, 30k miles, or whatever interval you use. On the other hand, if you are draining out "bad" fluid, then it has already done some damage.
No swimming pool I live by the Chesapeake Bay we used PH strips when I was a deck plate engineer in the Coast Guard. I have found that even the 5 yr so called long life gets real acidic at two years but the freeze/boil over remain good. I also have the HVAC mechanics that work for me use them to check the closed loop glychol chiller systems.
I have never changed the coolant in any car I've ever owned. The car body rusts away or the car dies from other causes. And I've owned cars 25 years and longer.
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