The necessity of the fan to keep the engine cool depends on the outside temp, the engine, the speed one is able to travel, amount of stop and go and several other factors. Engine overheating can quickly cause serious damage. IMO, coolant leaks are one of those issues that should be addressed ASAP. Same goes for a radiator leak.

After, say 100,000 miles, there is no way to predict when either will fail or if they will give you any warning so you can avoid a breakdown. Whether you replace now or when there are symptoms depends on your risk tolerance. My risk tolerance for a breakdown is not very high. I have towing insurance for up to 200 miles. In the past several years I haven't driven it anywhere that is more than 100 miles away based on age of vehicle and miles on the clock.

If you have a mechanical pusher fan, consider replacing with an electric fan. I upgraded the mechanical fan to an electric one, have done that on almost every vehicle I've owned. I have a new upgraded radiator in storage.

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X5 4.6 2002 Black Sap, Black interior. 2013 X5M Melbourne Red, Bamboo interior
Dallas