Scott Smith wrote:
I'm planning to convert the "Very Black" '88 from green to orange antifreeze. I have heard that a thorough flush is required since the two types of antifreeze don't mix.
I had planned to drain the system, refill with water, repeat until clear and drain again and add 2 gallons (or the proper mix). I plan to flush with distilled water.

My other two vehicles have been converted during water pump changes so I would like to keep the family consistent and environmentally friendly!

Any suggestions/cautions?


At the risk of starting another never-dying thread, here is a post from a couple of years ago.

At 03:20 PM 4/6/01, wrote:
Nobody mentioned this about DexCool:
"Dexcool is an excellent antifreeze to be used in brand new cars in which traditional phosphate/silicate antifreeze has never been used. However, if any traditional antifreeze has ever been used in your car's cooling system, it is strongly advised to avoid using Dexcool. This is because, short of a dangerous strong acid cleaning or complete replacement
of all parts within the cooling system, it is physically impossible to remove all residuals of phosphates and silicates - even with repeated flushing. If Dexcool is used in such a system, deposit formation will be almost instantaneous and will seriously affect your car's cooling system efficiency and performance. Because most corrosion occurs under such
deposits, it will also affect the long-term corrosion prevention in such a system as well."
(From the 'Tech Talk' section of the August, 1998 Roundel (BMWCCA magazine), page 92. This was an excerpt from an article written by Bill Siuru in the May '96 Skinned Knuckles. The excerpt is by Applied Chemical Specialities Co, a competitor of Havoline, which makes Dexcool.)
If this is true then would I be better off not replacing the antifreeze with DexCool if the car previously had the traditional antifreeze?

Needless to say, this got my attention, and I started a search for information on DexCool.

DexCool was developed and patented by General Motors and is produced by several companies under license. It is basically ethylene glycol inhibited with a combination of mono and dibasic carboxylic acids, although some products use a combination of sebacic acid and 2-ethylhexanoic acid supplemented with tolyltriazole. (just in case you were curious).

Texaco has a pretty thorough product sheet available at . Click on antifreeze, then DexCool.

Advantages of DexCool:
Conventional coolants are ethylene glycol with silicate and phosphate inhibitors to help reduce corrosion. These inhibitors are effectively depleted after only eighteen months to two years, so cooling system corrosion increases dramatically after two years service. In addition, the silicates are abrasive to water pump seals.
The OAT (Organic Acid Technology) additive package in DexCool contains no silicates and no phosphates. The OAT additives remain effective for five years of normal service. The elimination of silicates greatly improves water pump seal life.

Disadvantages of DexCool
It is slightly more expensive than convention coolants ($1- 2 per gallon), and is not as readily available.
It requires thorough flushing of the system if you are changing from conventional coolant, as we would be.
It does not work well in an open system, or a system that contains air.

Rumors and Reports
The Internet is great for spreading stories. Remember that everyone who starts these stories has an axe to grind, and money to make.  There appear to be two sources for the reports of problems with DexCool.
First - General Motors had/has some serious problems with corrosion and plugged heater cores on Blazers. GM says that the problems are due to two things: owners who run DexCool past its rated five-year lifespan; and owners who allow the system to run low on coolant for extended periods of time. The situation may be complicated by the persistent reports that GM sent most of those Blazers out of the factory with low coolant levels.

My discussions with Texaco engineers came up with some answers. Silicates in conventional coolants will "plate out" or coat metal surfaces inside the cooling system. If the cooling system gets low on coolant, the plated silicates will give some corrosion protection to the metal that is then exposed to hot, moisture-saturated air. DexCool has no silicates, so if the coolant level gets low, the metal exposed to hot, moisture-saturated air has no corrosion protection, and will corrode relatively quickly. The only place that there should be air in a 928 system is in the expansion tank, which is plastic.

The second source for the reports are statements by companies that make only conventional coolants with silicate/phosphate additives. Texaco flatly says that these reports are false, and have succeeded in forcing retractions from some published reports.

Texaco says that DexCool is fully compatible with conventional coolants, and that there will be no increased corrosion if the coolants are mixed. If, however, the coolants are mixed, with as much as 10% convention coolant in a DexCool system, the mixture has no more useable lifespan than the conventional coolants.

Texaco's Recommendations
Two different sources within Texaco's engineering departments investigated DexCool's application in the Porsche 928. They independently gave the same answers.
1) Texaco recommends the usage of DexCool in the 928, citing longer coolant life and longer water pump life. One engineer did say, however, IF the coolant is changed every two years, regardless of mileage, and IF the water pump is changed every 45 - 60,000 miles, there is little advantage in using DexCool.
2) If you are changing from conventional coolant to DexCool, Texaco recommends thoroughly flushing the cooling system twice with plain water as a minimum. It is better to flush the cooling system with plain water, followed by Prestone Heavy Duty cooling system cleaner, followed by another thorough flush with plain water.

My Conclusions
DexCool is great for the totally filled cooling system of most cars, especially those driven by owners who don't do maintenance. (How many people do you know who change their coolant every two years on their daily driver?)
DexCool is not acceptable for vehicles like my '74 Ford pickup, which does not have a coolant return system, and which typically have air in the cooling systems. (I'll be changing it back real soon now.)
DexCool is perfectly acceptable for usage in a 928.
DexCool has few advantages IF you change your coolant every two years and your water pump every 60,000 miles.

I hope that this answers most of your questions.

Wally Plumley
928 Specialists


>I am refilling the car with anti freeze and have been advised by the  auto store that if I am using the "Green" anti freeze, not to use the "red" environmentally safe anti freeze unless I flush twice as the two are  incompatible and I will build sludge and ruin the new water pump.
>Anyone else heard this or are they pulling my leg? Is there a good  additive for water pump lubrication?

If by "red" environmentally safe antifreeze, you mean coolant containing propylene glycol instead of ethylene glycol, that is mostly bogus marketing hype.

If you mean the orange DexCool, here is a post from last year.

If you use good coolant, you don't need water pump lubricant.
Wally Plumley


In case you missed Frenzy 8, Earl Gilstrom shared his latest findings on antifreeze, concluding with a high recommendation to switch to Zerex G05. The label specifies that it meets Chrysler & Ford requirements.

As background, I have been using red/orange Dex Cool, and Earl says it eats plastic (like water pump impellers and radiator tanks) and rubber. My 4 year old thermostat seat was shot when checked last month, so I have to agree with Earl. I plan multiple flushes and a switch to G05 soon, though I'm already too late to miss the first snowfall.

Joe Thrift