This is Ford's postition. Naturally they are going to be against other types of coolant, but they say universals do not generally meet the spec and silicates and nitrites are required.
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Some companies market a universal coolant, stating that their product can be used for all vehicle applications. Here is Ford Motor Company's official policy on these products.
Q: What is Ford's position on the use of "universal" coolants in Ford vehicles?
A: Ford does not have performance data for the multitude of engine coolants available in the aftermarket and therefore cannot recommend the use of any coolant except those approved by Ford Motor Company. Due to the complexity of cooling systems, no one coolant has been proven to work in all vehicles. "Universal" coolants generally do not contain silicates and nitrites, both of which are required for Ford vehicles equipped with Motorcraft Premium Gold Engine Coolant. Thus, these "universal" coolants generally do not meet Ford's coolant specification WSS-M97B51-A1.
Ford vehicles equipped with Motorcraft Premium Engine Coolant, meeting Ford specification ESE-M97B44-A, require silicates and, in the case of diesel engines, the use of Motorcraft Diesel Cooling System Additive, VC-8, which contains nitrites. Thus, these "universal" coolants may not be suitable for use in vehicles originally equipped with Motorcraft Premium Engine Coolant.
Based on blind laboratory ASTM testing performed in duplicate, two leading "universal" coolants currently in the marketplace did not meet the extended D2809 requirements of Ford's Motorcraft Premium Gold Engine Coolant specification, WSS-M97B51-A1.
The "universal" coolants may not be compatible with Ford's recommended supplemental coolant additive, Motorcraft Diesel Cooling System Additive, VC-8.
Use of non-approved "universal" coolants may lead to eventual engine damage or failure. Problems caused by use of non-approved "universal" coolant may not arise immediately, but may occur over longer periods of time due to additive compatibility issues.
Although the Ford New Vehicle Limited Warranty is not automatically voided upon the use of a non-approved coolant in Ford vehicles, if such use results in damage to the vehicle or its components, the cost of repairing the damage (and related damage) would not be covered by the Ford New Vehicle Limited Warranty.