SERVICE GUILD: RECONSTITUTED ANTI-FREEZE TESTING. Chevrolet Chevy MD P Bus Chassis 1988

VEHICLES AFFECTED: ALL MODELS ALL YEARS

RECONSTITUTED ANTIFREEZE

At present, three types of recycling systems are available:

1) chemical addition to coolant; 2) filtration and addition of supplemental additives; and 3) separation of pure glycol from used coolant and reinhibition.

1) Chemical Addition - NOT RECOMMENDED

With chemical addition, chemicals are added to the used engine coolant in an attempt to "clean up" the coolant. This system is the easiest since the only work involved is the addition of chemicals to the radiator. Most of these types of recycling systems use a strong acid to change precipitated corrosion products into a more soluble form. However, in addition to dissolving the corrosion products, the strong acid also attacks the corrodes the metals of the cooling system.

2) Filtration and Addition of Supplemental Additives - NOT RECOMMENDED

In this type of system, the used coolant is either taken out of the vehicle or a flush-type unit is connected to the cooling system. The current technology consists simply of filtration and reinhibition of the spent coolant. While this does remove suspended solids, filtration does nothing to remove harmful degradation and corrosion products that are soluble in glycol solution. The reinhibition step used in current recycling systems may fail to produce a coolant which adequately protects all metal including aluminum in the most critical heat transfer applications, such as occurs in the cylinder heads and blocks.

3) Separation of Pure Glycol and Inhibition -

The separation of pure glycol and the addition of fresh inhibitors is the ideal method for recycling coolants. Unfortunately, this method is expensive from both a collection standpoint and the technology available to economically extract pure ethylene glycol from used coolant.

At this time, General Motors does not endorse these practices or equipment.

Due to a worldwide shortage of ethylene glycol in 1988, some coolant manufacturers have started to mix other types of glycol in their coolant formulations; propylene glycol is the most common new ingredient. A hydrometer will not provide a correct measurement of freeze protection when anything other than ethylene glycol and water is being tested. The degree of inaccuracy will vary depending on the proportion of other glycols present in the coolant.

Hydrometers test the amount of glycol in a mixture by measuring the specific gravity of the mixture, the more ethylene glycol, the higher the float balls go, and the better the freeze protection. Because ethylene glycol and propylene glycol do not have the same specific gravities, hydrometer readings of mixtures containing propylene glycol give incorrect values.

As the shortage of ethylene glycol continues and/or worsens, more and more variations in antifreeze formulas will be marketed. It is, therefore, recommended that you purchase a "refractometer" and encourage your technicians to use it. Refractometers test for the amount of glycol in a coolant mixture by measuring the speed of light as it passes through the fluid and are not affected by the specific gravity of the glycol. The freeze protection of solutions of ethylene glycol in water, solutions of propylene glycol in water, and solutions of mixtures of propylene glycol and ethylene glycol in water may all be tested with sufficient accuracy using a refractometer.

The following refractometers are available from Kent Moore:

J 23688 Farhenheit scale, measures to -50F J 26568 Centigrade scale, measures to -45C DEG J 38633 Farhenheit scale, measures to -34F (for extreme cold weather regions)

The toll free number for Kent Moore is 1-800-345-2233.

Portions of this article were reprinted with permission, from Dow Chemical Canada, Inc., P.O. Box 1012, Sarnia, Ontario N7T 7K7.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.