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Matthew Wright

Coolant or Water?

By September 12, 2008

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This letter made me think, so I polled my less mechanically inclined friends and was surprised to find out how many people were in the dark on the subject of coolant:
Hi Matthew, I was just reading your maintenance guide at About.com and I have a couple of questions about my car's coolant. I drive a 94 Volkwagen GTI, and when I bought it there seemed to be only water in the coolant bottle. Is it possible to have run on just water without overheating? Or is this more likely a mix of water and coolant? In your guide you state that using tap water is harmful for the engine so I'm just wondering what the previous owner had in the cooling system. If it is indeed just distilled water and no coolant in the cooling system, could that have caused harm? I think I will flush out the cooling system and put in the OEM recommended coolant, is there any further steps you'd advise?
Thanks in advance for any help, Tim
The difference between running the proper mix of coolant or just water is huge. It's not enough for your radiator to be wet on the inside, coolant has properties that perform a number of different functions while it swooshes through your engine. The most obvious difference is the freezing point, if you live in a cold climate you'll crack your engine block if you have only water in there. But coolant also has a much higher boiling point than water, and can therefore hold a lot more heat without boiling over. Wait, there's more. The compounds in coolant fight corrosion in the radiator and other components it comes in contact with. Running water alone isn't going to stop the process, and can lead to premature failure of parts of your cooling system. Worse, tap water has its own bag of unwanted chemicals, and running your car on that can cause even more corrosion of parts. The bottom line? You must run coolant in your system no matter where you live. This is non-negotiable. If you suspect your car is without coolant, it's a good time to do a flush and fill of the system. It's not worth taking chances.

(Psssst ... if you've never checked your coolant before, here's how. We won't tell anybody.)

September 12, 2008 at 11:15 am
(1) Jon says:

This is a good bit of advice! I personally recommend using the waterless coolant by the brand, Evans, as it really isn’t affected by heat. It costs more than conventional coolant, but there’s no doubt that the motor is happier because of it.

September 13, 2008 at 10:37 am
(2) cactass dupree says:

It ought to be noted that some coolants are poisonest (sp). I drained my coolant back in the 70′s, went inside to eat a sandwich my wife had made for me. When I came out 2 morning doves were dead from sipping out of the collection pan. Needless to say I was bummed and learned a very important lesson. Thought I pass it along. peace!!

September 17, 2008 at 12:19 am
(3) Adam says:

Could be that the previous added water to the coolant resevor while antifreeze was in the radiator and motor and had run a little low. It is best to buy an inexpensive coolant checker at a local parts house and check the coolant when the motor is cold.

September 17, 2008 at 12:39 pm
(4) gw fourmyle says:

no doubt running h20 in passenger vehicles is trouble–but many race cars use it, one problem w/’coolant’ is it’s ‘slippery-index’–if there’s any way it may ‘breach’ a head-gasket?
far more likely than h20–but racers are only concerned w/1 race/engine–it’s interesting to note the old trick of NaSi for block/head sealing is still around, and now some mfgr. add a bit to their new car’s coolant–to prevent small ‘leaks from becoming a warranty-repair–they probably also toss-in what chemist term ‘catalyst-cross-linkers’–as NaSi is hardly compatible with most coolants.
still, i doubt you would be surprised at the #
of ‘not-worth-fixing’ cars using NaSi + pump-lubricant, anti-corrosives–still driving around.

September 17, 2008 at 5:54 pm
(5) Phil says:

As usual, Matt has covered the topic well, and the added readers comments add to the content. I’ll throw in a few lines from my experience.

While many of the automotive manufacturers are now installing “long-life” coolant in auto’s, we still need to be practical about coolant system maintainability as other items within the system come into play.

For example, the coolant system should still be flushed and all of the coolant replaced every 24 months/30,000 miles. If a metal component within the cooling system fails and is replaced (like the water pump,) do not use the old coolant as the seals and packing inside the water pump require the lubrication and anti-heat/friction properties not found in “used” anti-freeze.

Used anti-freeze (coolant) also becomes contaminated with heavy metals so do not dispose of it in your sink, toilet, or the corner storm drain. If you spill some in the driveway, use oil spill absorbent(kitty litter will work in a pinch)to pick up as much as possible and then flush with copious amounts of water being careful not to get any of that solution in the corner storm drain.

As already mentioned, keep it away from birds and other animals (especially cats and dogs) as even the latest environmentally friendly coolants are toxic to them. (They are attracted to them as they smell/taste sweet.)

Cheers, Phil

August 23, 2009 at 1:00 pm
(6) Doug says:

I have a high performance car that sees occasional track duty in a warm (SoCal) climate. What about running distilled water with Water Wetter?

February 10, 2012 at 7:20 am
(7) Adolf says:

God Bless America

March 13, 2012 at 6:55 pm
(8) Pat Garcia says:

I run my race car with water wetter and a pump lubricant runs purrrrrttty!!!!

April 28, 2012 at 11:58 pm
(9) sridhar says:


i want to know, if the term “coolant” means it cools the engine, or just keeps the water from getting evoporated, or cleans the passage of the radiator to reservoir – engine head path, or else?
what is the difference if the radiator is topped up with fresh purified-distilled water as and when necessary instead of adding coolant to water? Whether it is the coolant or water that cools the engine? what is the symptom that the coolant-water mixture should be replaced? what should be the optimum temperature reading difference during a hot summer of 40C (104F) with and without A/C in fiat uno diesel 2000? Is there a relationship between heat hike and stumbling of engine during such period and when the temp. indicator shows midway between 60F and 140F?

October 24, 2012 at 11:39 pm
(10) KIMOSABE says:

I live in wisconsin ,and we get from 100 degrees to -5 during the year.I only use Gatorade ,(green bottle) and works like a charm,no mixing needed.

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