Hosted by SupraMania!

Go Back   MKIII Tech > Technical > Cooling System
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Thread Tools Display Modes
Old 10-12-2006, 12:18 AM   #1
Super Moderator
jetjock's Avatar
Join Date: Jun 2006
Location: The Ford Galaxy
Posts: 258
Default Coolants and cooling systems.

Well, I see some things in this section I can expand on so I'll throw in my two cents.

First, keep in mind that coolant color means nothing these days. It's just dye. Anyone who talks to you about coolant in terms of color is a sure sign they don't know what they're talking about. Two coolants with similar colors may have different chemistry and two coolants with different colors may have similar chemistry. Furthermore color can change when different coolants are mixed.

Generally speaking coolants are either ethylene glycol (EG) or propylene glycol (PG) with EG far and away the most common. EG coolants are typically around 90% glycol with the rest being water and the additive package. The "add pack" is what determines the coolant's corrosion inhibiting chemistry and how it's accomplished. Other than these inhibitors there is *no* difference between any EG based coolant brand. That's right...the much touted Toyota OEM coolant is 95% same as any other coolant.

Older coolants, the so called "conventional" types, are called Inorganic Acid Technology (IAT) and typically (but not always) use silicates for corrosion protection. The Prestone your dad used was a conventional coolant. Silicates work by "plating" a very thin layer of glass-like substance on every surface in the cooling system including hoses and can quickly stop damage done by cavitation erosion and other harmful effects that occur. The downside is they don't last long, can fall out of solution after time (about 2 years) and either collect in the bottom of the radiator where they aren't doing anything helpful or, even worse, circulate around the system as micro abrasives. Silicates are why older coolants had to be changed fairly often. They're still around but the silicate levels are much less than before and the chemistry has been altered to improve stability.

Modern long life coolants use other chemicals to prevent corrosion through the process of passivation. The coolants are referred to as either Organic Acid Technology (OAT) or Hybrid Organic Acid Technology (HOAT). HOAT is a mix of IAT and OAT, hence the name. All result in long life because the inhibitors used remain active for years. The downside of OAT coolants is they need time to passivate cooling system metals and if damage occurs to the barrier it can take time to repair. HOAT solves this problem by using small amounts of silicates or nitrites (typically <300 ppm) for fast acting protection in addition to the long life provided by it's OAT inhibitors. It's the best of best worlds.

GM's Dex-Cool was the first OAT marketed and is produced today as "Dex Clones" under license. Some people swear by it but I recommend against Dex in any engine other than for which it was designed and even then I don't like it. Experience has indicated the coolant system must be air tight or it'll sludge. The problem appears to be associated with the use of 2-ethylhexanoic acid (2-EHA), one of the coolant's inhibitors (the other is sebacate), which is a plasticizer. In fact there has been lawsuits regarding the damage allegedly done by "Death-Cool". Toyota specifically states not to use it.

Which brings us to Toyota's coolant. During the 80/90s Toyota Red was an IAT conventional coolant containing phosphate as the inorganic inhibitor. It avoided silicates altogether. Phosphates are fast acting (but still short lived) and work well on aluminum. These days Toyota Red is an HOAT using sodium benzoate as the organic and potassium hydroxide (KOH) as the inorganic.

All this doesn't mean you need to use genuine Toyo though because other HOAT coolants as as good or better. Of those I prefer the G-05 fluid developed by BASF, a company that knows a thing or two about chemicals in general and coolants in particular. Anyway, the G in G-05 stands for Glysantin:

BASF invented glycol based automotive antifreeze 75 years ago and G-05 has won numerous technical awards since it's introduction. Glysantin coolants are factory fill for all Damier-Chrysler products and has been used by Mercedes since the company's birth. I've run it in my Supra without problem for years. The one I use is Zerex (Ashland Chemical's Valvoline brand) G-05. It's low silicate, low PH, long life HOAT.

In 2009 Zerex introduced a new coolant called Zerex Asian Vehicle:

This is the first (and only) phosphated non-OEM coolant chemistry available in the US. It only comes in premixed. It's as close to OEM as one can get but, like OEM coolant, is a product of marketing and not real necessity.

That said you can't go wrong using Toyota's coolant. Too expensive for my tastes however and since G-05 is a near universal coolant it's all I need to keep around. G-05 uses sodium benzoate as the organic acid, exactly the same as Toyota Red, which these days is also HOAT. In fact the main difference between G-05 and OEM is the use of sodium tetraborate (you know it as borax) and sodium nitrite as the inorganic inhibitors. Other than this and dye color (and the price of course) there is little difference between the two.

One issue to be concerned with is the use of high lead bearing solders in older aftermarket radiators and heater cores. For example industry tests of the newer Toyota extended life coolant show a substantial weight loss in these items, both in a 50-50 mix and in a 33% coolant mixture (solder corrosion is actually much greater in the more diluted solution). If you have to change a radiator or heater core use aluminum or be sure the lead content in the copper/brass unit is low. And remember, if you’re replacing aluminum parts on an engine, such as a water pump or even a cylinder head, the part’s coolant passages are virgin: the only protection against corrosion they have is naturally occurring aluminum oxide. In such cases don't reuse old coolant. I know, I know...but some people do.

As with oil most owners change coolant more often than needed. Best is to either use coolant test strips or electrically measure the coolant. Coolant electrolysis (caused by an electrical current passing through the coolant) is bad news and can cause component failures in as little as two months. You can check for this by placing one probe of a voltmeter on the negative of the battery and the other in the coolant of the radiator neck. (Don't allow the probe to contact the radiator). Measure first with electrical accessories off and then with them all on. Any voltage over .3 volts means the coolant must be changed and the cause of voltage over .5 must be found and corrected.

Do this at least once a year and if you find over 300 millivolts don't ignore it because it will destroy even a properly maintained cooling system. I can't stress this enough. It's the cause of many repeat radiator or heater core failures and is *the* reason for ECD (electrochemical degradation) hose damage, the cracking you see on the inside of hoses near the ends where they contact to metal fittings. Which reminds me, the common belief a hose is good unless it's mushy is wrong. A hose can feel perfect but be ready to fail from damage done by this process.

Change a conventional silicated coolant every two years. If you use an OAT or HOAT coolant change it every 5 years. I do a simple radiator dump and refill every two years. This process keeps the corrosion package fresh, is easy to do, and eliminates the need for flushing. I also run a coolant filter.

Other points: Never use 100% coolant or 100% water in a street car. A 60/40 or 50/50 mix of coolant and distilled water is best for all but Alaskans. Speaking of which note how the freezing point of coolant increases as the percentage of glycol it in increases. Definitely a case of more not being better:

I disagree with using surfactants like Water Wetter. Surfactant products are made for use in 100% water systems because, well, that's what surfactants do...they break the surface tension of water, not glycol. In fact there is a simple experiment you can do in your kitchen that proves WW doesn't work all that well in a water/glycol mix but I'll leave that for another time. The stuff also has some history of producing a slime byproduct when used in glycol. WW does one thing beneficial however: it replenishes the coolant's anti-corrosion properties.

Always top up your cooling system with a coolant mix. Never use water alone or you'll be diluting the coolant. For real freeze protection forget hydrometers, use a refractometer for accurate measurements. Remember, a coolant's ability to prevent freezing or boil over never changes. The reason you change coolant is much the same reason you change oil: to remove contaminants and replenish the additive package, in this case for anti-corrosion. You may want to consider a coolant filter too. The one I run on my car keeps the coolant and system very clean.

Finally, when troubleshooting cooling problems remember the basics. Coolant may remove heat from the engine but it's airflow that removes heat from the coolant. Keep the fan, fan clutch, shroud, and radiator side seals in good condition and the exterior surfaces of the radiator, intercooler, and A/C condenser clean.

There's more to know. Coolant is like oil: few bother to really learn about it and simply use what they "think" is best. The truth is out there and, as with all things technical, it's in learning the science behind how something works. Educate yourself about coolant chemistries and proper cooling system maintenance and your cooling system will thank you for it. And remember: data from the NHTSA shows that, year after year, the most common cause of automotive breakdown is cooling system related.
jetjock is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

All times are GMT -4. The time now is 11:28 PM.

Powered by vBulletin® Version 3.6.9
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
MKIII TECH hosting, software and bandwith brought to you by a grant from, ad revenue and from member donations. Thank You!