The main purposes for engine coolant are heat transfer from the engine to the radiator, corrosion prevention and lubrication of seals.
There are two major formulations of engine coolants. They are propylene glycol and ethylene glycol.
Propylene glycol is less toxic and is preferred by some manufacturers. Ethylene glycol is more widely used.
Among these two formulations, there are subcategories of the formulations-they are as follows:
IAT-Inorganic Acid Technology. This is a more conventional type of coolant used in older engines with cast-iron parts.
OAT-Organic Acid Technology. This is used in modern engine with aluminum parts. It is also longer lasting than IAT.
HOAT-Hybrid Organic Acid Technology. This is used in high performance engines. It is the best of both worlds.
Engine coolant manufacturers are very proprietary and do not adhere to a particular formulation. It is best to follow vehicle manufacturer’s recommendations.
BMW recommends an ethylene glycol based, low silicate, HOAT engine coolant, not containing nitrites, amines, phosphates, or borates in their water-cooled motorcycles. I found no coolant replacement interval from BMW. The most accepted interval is two years or 24,000 miles. Try to save some extra coolant for top-offs.
I have two recommendations for BMW motorcycle coolants. One is Zerex G48 part number 861583. This is made by Valvoline and some say they make the engine coolant for OEM BMW. This is pre-diluted (no water needed) and is is widely available. The other one is OEM BMW. The part number is 82141467704. This is concentrated and need to be mixed 50/50 with distilled water. The BMW may be a better value as you get twice as much after dilution.
Here are some tips for motorcycle engine coolant:
1) Do not mix coolants of different types or brands. Mixing coolants can cause reactions from the additives that can lead to engine damage and voiding of the manufacturer’s warranties. The color of the coolant is proprietary and can mean different things to different manufacturers. If there is no coolant available that matches the coolant in your engine, use distilled water to top-off. If you had to add a lot of water, check for leaks and replace the coolant to prevent over-dilution.
2) Always use distilled water to dilute the coolant. Tap water can contain minerals and other contaminants that can degrade it.
3) There is are no such thing as forever fluids. Almost all fluids need replacing periodically.