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#615413 - 08/27/05 10:39 AM Does coolant turn into acid?
adreed24 Offline

Registered: 01/28/05
Posts: 117
Loc: Baltimore, Maryland U.S.A.
I am asking this question about conventional, old-fashioned, coolant/antifreeze, that has been used in cars for many, many years.

I have heard a story about coolant/antifreeze for years, and I'd like to know if there is any truth to it.

I heard that if you don't regularly change your coolant/antifreeze (when your vehicle manual calls for it), that the old coolant/antifreeze will turn into an acid, that will eat away at your cooling system and destroy the radiator.

Does this make any sense, or is it just some myth that I heard years ago?

If it is true, how long does it take for this "acid formation" to start to cause damage?

Would this "acid formation" eventually happen to "extended service" or "longer life" coolant/antifreeze too, if it were not changed at the proper time?

Thanks in advance!

#615414 - 08/27/05 10:54 AM Re: Does coolant turn into acid?
Ray H Offline

Registered: 01/16/03
Posts: 4478
Loc: Southern California
When the corrosion inhibitors, buffers, and stabilizers in finished conventional antifreeze are exhausted, corrosive acids will form as the result of their breakdown byproducts. But the chief ingredient, ethylene glycol (~95%), is very chemically stable. The extended life antifreezes using OAT chemistry are quite long-lived in a properly sealed system. DEX-COOL can be problematic if leakage allows air into the system.

#615415 - 08/27/05 11:00 AM Re: Does coolant turn into acid?
adreed24 Offline

Registered: 01/28/05
Posts: 117
Loc: Baltimore, Maryland U.S.A.
So, does that mean that only a small percent of the liquid (coolant & water) in the cooling system, becomes acidic, since ethylene glycol is pretty stable?

What if the water in the system is not distilled or de-ionized, but just household tap water?

#615416 - 08/28/05 01:46 AM Re: Does coolant turn into acid?
Big Jim Offline

Registered: 09/24/04
Posts: 1571
Loc: Thousand Oaks, CA
Prior to OAT technology, one of the important parameters of any coolant blend was/is reserve alkilinity. That is the ability to resist becoming acidic. One of the ways that coolant is tested to see how it is holding up is a PH test.

OAT coolants are much more stable to bigin with so reserve alkilinity is not particularly applicable.

#615417 - 08/28/05 08:26 AM Re: Does coolant turn into acid?
adreed24 Offline

Registered: 01/28/05
Posts: 117
Loc: Baltimore, Maryland U.S.A.
I guess I could do a PH test with the test strips that Prestone makes. I don't know if they still make them. Does anyone else make/sell them?

Are PH test strips accurate?
How accurate?

#615418 - 08/28/05 03:15 PM Re: Does coolant turn into acid?
Mickey_M Offline

Registered: 08/13/04
Posts: 1001
Loc: Baltimore
A variety of test strips are used regularly in over-the-road trucks:

You should be able to locate strips at distributors that sell to the truck market, including NAPA. Be sure the strips you buy are designed for your coolant - the target Ph of some of the newer coolants are different than the older coolants.

You'll also find outfits that will do an analysis of your coolant much like you can have your used oil analysed.

The reason why you see neither much in the automotive market is that the cost of the strips and the analysis are pretty high compared to the cost of just replacing the coolant in a small cooling system.


#615419 - 08/29/05 07:56 AM Re: Does coolant turn into acid?
Big Jim Offline

Registered: 09/24/04
Posts: 1571
Loc: Thousand Oaks, CA
Many dealers use strips for checking coolant condition, especially if they use BG or MOC products. The last I knew, they didn't have strips for OAT or HOAT coolants though.

#615420 - 08/29/05 09:18 AM Re: Does coolant turn into acid?
Bearracing Offline

Registered: 08/08/05
Posts: 14
Loc: Reno, NV
Big Jim,

Just a couple of weeks ago, the local BG rep showed me some newly released pH test strips (from the Dana Corporation I believe) designed for OAT and HOAT coolants. Fairly cost prohibitive though, I was quoted $25 for a 50 count container.

#615421 - 08/29/05 10:32 AM Re: Does coolant turn into acid?
Big Jim Offline

Registered: 09/24/04
Posts: 1571
Loc: Thousand Oaks, CA
I'll bet that they are not used by the writers everytime they do a drivway inspection. They will probably come down in price soon enough.

#615422 - 09/15/05 04:13 AM Re: Does coolant turn into acid?
Ken2 Offline

Registered: 12/02/02
Posts: 6375
Loc: Washington St.
The corrosion inhibitors do become depleted. An easy check is with a digital voltmeter.

Set the meter on a low DC voltage scale. Put the + probe on the battery negative post and the - probe into the cool radiator filler opening, under the coolant level, but not touching any metal. (I may have the polarities backwards, but it doesn't matter.)

An excellent reading is .1 volts or less. Anything above .3 to .4 volts is time to flush and renew the coolant.


#615423 - 09/15/05 12:14 PM Re: Does coolant turn into acid?
Shannow Offline

Registered: 12/12/02
Posts: 35003
Loc: Oz
good tip.

I use the Castrol test strips that also give you an indication of glycol content (not that I need it).

$30 for 50 of them, which is pretty cheap seeing as it's about the same cost as a coolant change.

#615424 - 09/16/05 12:35 AM Re: Does coolant turn into acid?
oilmanatwork Offline

Registered: 08/04/05
Posts: 8
Loc: Powell River BC
The volt meter trick is a good cost effective way. As cars come through my quick lube I check each cooling system for freeze/ boil point, Acidity and check the cap. Its totaly amazing how many caps fail. Even on vehicals as new as 04 and low low milage. I like the PH strips as its a little easier for the average person to understand. Its amazing how many people who think there mechanicaly inclined look at me and tell me I'm full of BS when I try to tell them the merits of Akalinaty, -37 degrese centigrade minimum freeze point and rad pressue.

#615425 - 09/16/05 01:58 PM Re: Does coolant turn into acid?
oil pan 4 Offline

Registered: 02/24/05
Posts: 257
Loc: Hampton, VA
Change your cap every coolant flush or 2yr.
It will keep air out of the system and when you keep out the air you keep the rust away.

#615426 - 09/16/05 08:21 PM Re: Does coolant turn into acid?
Kestas Offline

Registered: 06/04/02
Posts: 11607
Loc: The Motor City
So, what pH do we aim for?