REDUCED COOLANT FLOW AND/OR ENGINE OVERHEAT CONDITION

MOST OF THE AUTOMOTIVE GRADE ANTIFREEZE FORMULATIONS SOLD TODAY CONTAIN THREE TO EIGHT TIMES AS MUCH SILICATE AS THEY DID SEVERAL YEARS AGO. THE SILICATE CONTENT WAS INCREASED TO PROVIDE CORROSION PROTECTION FOR THE GREATER AMOUNT OF ALUMINUM USED IN AUTOMOTIVE COOLING SYSTEMS TODAY. CORROSION INHIBITOR SUPPLEMENTS, USED TO MAINTAIN CORROSION PROTECTION IN HEAVY DUTY DIESEL ENGINE COOLANTS, ALSO CONTAIN SILICATES. IF AN ANTIFREEZE LARGE AMOUNTS OF CORROSION INHIBITOR SUPPLEMENTS ARE USED, THE EXCESS SILICATE WILL "DROP OUT" OF THE COOLANT AND FORM SILICA-GEL RESULTING IN REDUCED COOLANT FLOW AND/OR ENGINE OVERHEATING. THIS GEL IS A NON ABRASIVE MATERIAL WHICH TAKES ON THE COLOR OF THE ANTIFREEZE OR INHIBITOR SUPPLEMENT USED IN THAT SYSTEM. WHEN DRIED, THE SILICATE APPEARS AS A WHITE POWDERY DEPOSIT. SILICATE "DROP OUT" MAY ALSO OCCUR IN COOLANTS USING EXTREMELY HARD WATER AND/OR UNUSUALLY HIGH OPERATIONAL TEMPERATURES. THE FOLLOWING RECOMMENDATIONS ARE MADE TO PREVENT SILICATE GEL FORMATION: 1. USE ANTIFREEZE THAT MEETS THE GM 6038M FORMULATION, WHICH LIMITS THE AMOUNT OF SILICATE TO .15% MAXIMUM. OTHER ANTIFREEZE FORMULATIONS MEETING THE 0.1% MAXIMUM SILICATE LEVEL AND THE GM 1825M OR GM 1899M PERFORMANCE SPECIFICATIONS ARE ALSO ACCEPTABLE FOR USE (GM PART NUMBER 1052753). 2. USE ANTIFREEZE SOLUTIONS AT THE CONCENTRATION REQUIRED FOR FREEZE PROTECTION IN YOUR OPERATIONAL AREA, BUT DO NOT USE MORE THAN 67% ANTIFREEZE OR LESS THAN 30% ANTIFREEZE. 3. NEVER USE 100% ANTIFREEZE WHEN ADDING COOLANT. MIX THE MAKEUP SOLUTION AT THE SAME CONCENTRATION AS THE ORIGINAL. 4. WATER HARDNESS SHOULD NOT EXCEED THESE LIMITS: CHLORIDE 40 PPM 2.5 GPG SULFATES 100 PPM 5.8 GPG TOTAL DISSOLVED SOLIDS 340 PPM 20.0 GPG TOTAL HARDNESS 170 PPM 10.0 GPG PPM = PARTS PER MILLION GPG = GRAINS PER GRAM 5. IF YOU ENCOUNTER SILICATE GELATION, REFER TO OEM ENGINE MANUFACTURER'S RECOMMENDATIONS OR CONTACT THE NEAREST OEM DISTRIBUTOR. THE FOLLOWING ARTICLES HAVE BEEN PUBLISHED ON THE SUBJECT OF SILICATE GELATION. - SAE TECHNICAL PAPER SERIES NO. 852327, "SILICATE GELATION IN HEAVY DUTY DIESEL ENGINE COOLING SYSTEMS" - PREPARED DECEMBER, 1985, BY: R. D. HERCAMP, CUMMINS ENGINE COMPANY, INC. R. D. HUDGENS, FLEETGUARD, INC. - CUMMINS SERVICE PARTS TOPICS - "OVERCONCENTRATION OF ANTIFREEZE AND/OR SUPPLEMENTAL COOLANT ADDITIVES", JUNE, 1985, NO. 85-T-2, FILE 8. - DDA SERVICE TOPICS - "COOLANT FOR DETROIT DIESEL ENGINES", FORTY- FIFTH YEAR, NUMBER 3, JULY-SEPTEMBER, 1985.

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.