Search the web and you will find huge amounts of mis-information on engine coolants

This is especially common in the case of the orange GM coolant, Dexcool.  Statistically, there are no less problems with green, yellow, red or any other coolant on the market.  Properly serviced, all coolants work well.  Improperly serviced all coolants have problems.

Almost all coolant is ethylene glycol based.  Despite similar chemical makeup, because of the difference in corrosion protection, different coolants should not be mixed or interchanged.  Dexcool is a hybrid-organic acid technology (HOAT) coolant.  This has to do with the corrosion protection strategy and I will not bore the reader with the details.  Other coolants use various other methods.  What is important is to put back what is specified and to do it in the proper way.

GM has used Dexcool coolant in many millions of vehicles since 1996.  In thousands of cooling systems, I am yet to see a problem I can relate to Dexcool coolant.  Most problems with Dexcool as other coolants, stem from over-extending it’s capability.  GM states five-years and a differing amount of mileages on their vehicles.  Watching only the mileage is a big mistake.  As with most coolant, age is the more important factor.  Chemical reactions (loss of corrosion protection) occur over time.  This occurs twenty-four/seven and has little to do with mileage.  Unfortunately, people tend to think more in terms of mileage.

The coolant in a one year old vehicle, with 100,000 miles is likely still be very usable.

A six-year old vehicle with 20,000 miles may be seriously depleted and causing damage.

Five years is the maximum life of Dexcool.  It is completely depleted by this age.

Five years begins when the vehicle is manufactured, not delivered to the customer.

Five years applies to the initial factory fill, when everything is new.

Other manufacturers specify three to five years and Dexcool reverts to three years after the first change.  More accurate is to determine service life based on pH and specific gravity measurement.  A pH below 7.0 means the coolant is acidic.  This can rapidly destroy the cooling system.  This sometimes occurs closer to three-years than five.  Several factors can also shorten this considerably:

• Diluting the coolant by adding water, such as with leaks

• Air entering the system, such as with leaks or a radiator bad cap

• Contaminating the coolant with corrosive chemicals and minerals that can be in tap water.  Distilled water or factory premixed coolant should be used

• Improperly mixing the coolant, less than 50/50 or physically with distilled water


• Not pre-mixing the distilled water and coolant before pouring into the system

Coolant should always be pre-mixed, 50/50 before pouring into the cooling system.  Since coolant is considerably heavier than water, the two may never mix in the cooling system.  This leaves heavier coolant (which ironically does not cool) in the lower part of the system.  The lighter (and corrosive) water tends to circulate in the top of the system, where it eats away at the radiator, heater core and cylinder heads.

As mentioned earlier, coolant does not cool the engine.  It provides corrosion resistance, freeze and boil protection, but water does the cooling.  Mixing more than fifty percent coolant can affect cooling.  Less than fifty percent gives inadequate protection.  

Draining only the radiator causes a similar problem.  This removes about sixty-percent of the old mixture.  If the remaining forty-percent is depleted, adding a fresh 50/50 batch can result in almost twenty-percent less protection than needed.  Not premixing can make this much worse.  

Improperly servicing the cooling system can be as bad as no service at all

Under ordinary conditions, flushing the system is almost never needed.  Replacing the coolant before 100% depletion will help a great deal.  Being proactive with a cooling system and following simple guidelines will prevent most problems.

Flushing water through a corroded system does little more than further disturb the final mixture.  If the system is corroded, professional cleaning by removing the engine block plugs and/or core plugs is better.  This also allows removal of more of the contaminated coolant.

This copper heater core is leaking due to corrosion from improper coolant

Freeze plug or core plug rusted through by corrosion from improper coolant

Air entering the cooling system will drastically aggravate corrosion

Cooling systems are sealed to prevent the introduction of air.  The initial seals are on the radiator cap.  Radiator caps are fairly complex, do a lot of work and often fail.  Checking the cap annually and replacing and worn or damaged cap can prevent a great deal of cooling system issues.

The cap is also designed to control pressurization of the system.  Pressurization raises the boiling point of the coolant.  With a precisely calibrated spring and valves the cap keeps air out of the system as the coolant expands and contracts from heating and cooling.

Some systems accomplish this by use of a reservoir.  When the coolant expands, it flows to the reservoir.  As the system cools the coolant returns to the radiator.  This system depends on a syphon effect.  Unfortunately if the system gets too low, the syphon can be broken.  Filling the reservoir will not fill a low radiator in this case.

Many vehicles now use a surge-tank system.   With this system the filler cap is normally on the surge tank, rather than the radiator.  In this system, coolant basically flows all of the time, helping to purge air from the system.  Expansion and contraction of coolant is allowed by the pressurized surge tank.

Many system also have bleeder screws.  After service, these screws are opened to allow any trapped air to be removed.  Simply open the screw and tighten after all air has been removed.  Final bleeding is by allowing the vehicle to reach full operating temperature and cooling back down.  Once fully cooled check the coolant level again and fill as needed with pre-mixed coolant.  While performing this final bleeding, the heater should be kept on maximum heat with the vehicle doors left open.

Regular, proper service can prevent almost all cooling system problems.  Cooling system inspection should be part of your annual general inspection.  Let AGCO show you other ways to prevent major problems.  AGCO, it’s the way to go!