distilled water
MBWorld Fanatic!
Joined: Mar 2006
Posts: 4,278
Likes: 377
From: San Jose area
'19 E63S sedan
Before batteries were sealed, distilled water was recommended for topping them up. The calcium salts that make water hard can shorten lead-acid batteries.
It's an old-wives tale that distilled water is better for a cooling system. Unlike old, unsealed batteries that needed frequent water top ups, a cooling system is sealed.
Very hard water has 10 grains per gallon of minerals (mostly calcium salts). Figure 10 gallons of water in your cooling system (an overestimate because you should have 50% antifreeze). That's a maximum of 100 grains of minerals. A grain is 65 milligrams, so even hard water will put 6.5 grams or about 1/4 ounce of scale-forming minerals in your engine. Only a tiny percentage of that can precipitate out in the radiator. You'll never see it in the real world.
On the other hand, totally demineralized water (distilled or deionized) is more corrosive to aluminum than water with some calcium in it. You can think of the tap water as "metal-saturated" (after all, calcium is a metal) while the distilled water is hungry to dissolve some metal. So while it never made any difference, distilled water was harmless to old iron-and-steel cooling systems but it is not a good idea for modern easily corroded aluminum engines.
It's an old-wives tale that distilled water is better for a cooling system. Unlike old, unsealed batteries that needed frequent water top ups, a cooling system is sealed.
Very hard water has 10 grains per gallon of minerals (mostly calcium salts). Figure 10 gallons of water in your cooling system (an overestimate because you should have 50% antifreeze). That's a maximum of 100 grains of minerals. A grain is 65 milligrams, so even hard water will put 6.5 grams or about 1/4 ounce of scale-forming minerals in your engine. Only a tiny percentage of that can precipitate out in the radiator. You'll never see it in the real world.
On the other hand, totally demineralized water (distilled or deionized) is more corrosive to aluminum than water with some calcium in it. You can think of the tap water as "metal-saturated" (after all, calcium is a metal) while the distilled water is hungry to dissolve some metal. So while it never made any difference, distilled water was harmless to old iron-and-steel cooling systems but it is not a good idea for modern easily corroded aluminum engines.
MBWorld Fanatic!
Joined: Nov 2001
Posts: 5,851
Likes: 196
From: Huntington Beach, Ca.
'17 Jaguar XF
Before batteries were sealed, distilled water was recommended for topping them up. The calcium salts that make water hard can shorten lead-acid batteries.
It's an old-wives tale that distilled water is better for a cooling system. Unlike old, unsealed batteries that needed frequent water top ups, a cooling system is sealed.
Very hard water has 10 grains per gallon of minerals (mostly calcium salts). Figure 10 gallons of water in your cooling system (an overestimate because you should have 50% antifreeze). That's a maximum of 100 grains of minerals. A grain is 65 milligrams, so even hard water will put 6.5 grams or about 1/4 ounce of scale-forming minerals in your engine. Only a tiny percentage of that can precipitate out in the radiator. You'll never see it in the real world.
On the other hand, totally demineralized water (distilled or deionized) is more corrosive to aluminum than water with some calcium in it. You can think of the tap water as "metal-saturated" (after all, calcium is a metal) while the distilled water is hungry to dissolve some metal. So while it never made any difference, distilled water was harmless to old iron-and-steel cooling systems but it is not a good idea for modern easily corroded aluminum engines.
It's an old-wives tale that distilled water is better for a cooling system. Unlike old, unsealed batteries that needed frequent water top ups, a cooling system is sealed.
Very hard water has 10 grains per gallon of minerals (mostly calcium salts). Figure 10 gallons of water in your cooling system (an overestimate because you should have 50% antifreeze). That's a maximum of 100 grains of minerals. A grain is 65 milligrams, so even hard water will put 6.5 grams or about 1/4 ounce of scale-forming minerals in your engine. Only a tiny percentage of that can precipitate out in the radiator. You'll never see it in the real world.
On the other hand, totally demineralized water (distilled or deionized) is more corrosive to aluminum than water with some calcium in it. You can think of the tap water as "metal-saturated" (after all, calcium is a metal) while the distilled water is hungry to dissolve some metal. So while it never made any difference, distilled water was harmless to old iron-and-steel cooling systems but it is not a good idea for modern easily corroded aluminum engines.
Super Member
Joined: Oct 2005
Posts: 584
Likes: 3
From: Northern NJ
E90 N54 & W251
I've done a coolant flush on my CL recently and used distilled water. According to StarTuned magazine and WIS, they specify the use of distilled water versus tap or even spring water. At the time I figured for the extra $2.00, why not. Would the car implode if you used tap water? Of course not; but distilled is what's officially advised. Whoover does bring up some compelling points though.
The full article:
https://www.mbwholesaleparts.com/Sta...8StarTuned.pdf
Excerpt from above article on Water Quality:
"In this article, we discussed proper cooling system service procedures, anti-corrosion antifreeze and tools to test and exchange the coolant. One more subject we need to discuss is something we very often take for granted. That is water supply. "City" water for drinking is treated. It contains fluoride or chloride salts due to the treatment, so it is not desirable to mix it with coolant. Do not use this, or hard water, in Mercedes-Benz cooling systems. In the odd chance you have a supply of spring water, either bottled or from a well, do not use this, either. Bottled water is not regulated and probably contains minerals that can react with engine components, and also acts as an abrasive when passing through the cooling system. Instead, use distilled water. It is the best to use since it contains no additives. The slight additional cost of distilled water should not significantly increase the cost of the overall cooling system service and eliminates harmful contaminants."
The full article:
https://www.mbwholesaleparts.com/Sta...8StarTuned.pdf
Excerpt from above article on Water Quality:
"In this article, we discussed proper cooling system service procedures, anti-corrosion antifreeze and tools to test and exchange the coolant. One more subject we need to discuss is something we very often take for granted. That is water supply. "City" water for drinking is treated. It contains fluoride or chloride salts due to the treatment, so it is not desirable to mix it with coolant. Do not use this, or hard water, in Mercedes-Benz cooling systems. In the odd chance you have a supply of spring water, either bottled or from a well, do not use this, either. Bottled water is not regulated and probably contains minerals that can react with engine components, and also acts as an abrasive when passing through the cooling system. Instead, use distilled water. It is the best to use since it contains no additives. The slight additional cost of distilled water should not significantly increase the cost of the overall cooling system service and eliminates harmful contaminants."
MBWorld Fanatic!
Joined: Mar 2006
Posts: 4,278
Likes: 377
From: San Jose area
'19 E63S sedan
Ask any garage to show you their supply of distilled water. It's a crock. "Fluoride or chloride salts" is a meaningless phrase. For one thing, these non-metallic anions are not an issue -- it's the trace metallic cations. For another thing, deionized water (which is what much "distilled" water really is) has more chloride from the ion exchange process than tap water.
And the notion that bottled water can act as an abrasive is pretty loony too. How much sand do you normally find in bottled water?
http://www.royalpurple.com/radiator-additive.html
Royal purple (click >> read more) is explicit about not using distilled water, as are other "experts."
Bottom line: I doubt any kind of water that's fit for drinking will harm an engine, but overly soft water in an aluminum system is marginally counter-productive.
And the notion that bottled water can act as an abrasive is pretty loony too. How much sand do you normally find in bottled water?
http://www.royalpurple.com/radiator-additive.html
Royal purple (click >> read more) is explicit about not using distilled water, as are other "experts."
Bottom line: I doubt any kind of water that's fit for drinking will harm an engine, but overly soft water in an aluminum system is marginally counter-productive.
Super Member
Joined: Oct 2005
Posts: 584
Likes: 3
From: Northern NJ
E90 N54 & W251
Ask any garage to show you their supply of distilled water. It's a crock. "Fluoride or chloride salts" is a meaningless phrase. For one thing, these non-metallic anions are not an issue -- it's the trace metallic cations. For another thing, deionized water (which is what much "distilled" water really is) has more chloride from the ion exchange process than tap water.
And the notion that bottled water can act as an abrasive is pretty loony too. How much sand do you normally find in bottled water?
http://www.royalpurple.com/radiator-additive.html
Royal purple (click >> read more) is explicit about not using distilled water, as are other "experts."
Bottom line: I doubt any kind of water that's fit for drinking will harm an engine, but overly soft water in an aluminum system is marginally counter-productive.
And the notion that bottled water can act as an abrasive is pretty loony too. How much sand do you normally find in bottled water?
http://www.royalpurple.com/radiator-additive.html
Royal purple (click >> read more) is explicit about not using distilled water, as are other "experts."
Bottom line: I doubt any kind of water that's fit for drinking will harm an engine, but overly soft water in an aluminum system is marginally counter-productive.
I never really gave it much thought either way, but since I was DIY, I figured I'd follow the recommendations as specified. Your posts on this topic have been very insightful.
What's funny is I can see future readers go through this post and still be unsure of Distilled versus Regular water.
I guess it's all good either way.
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