Please forgive me for overlooking the manual transmission. We know we can rule out a leaking cooler inside the radiator. If you don't see oil floating on top of the coolant in the reservoir, it is likely you don't actually have a problem. It's a better bet you're seeing some residual additive in the antifreeze or perhaps a little grease or assembly lube from the water pump.
Regardless, if you don't know the history of the coolant, consider having the cooling system flushed and refilled. Antifreeze will always be antifreeze, but it's the additives in it that wear out in about two years. Also, it is normal for the coolant to become acidic over time and that leads to corroded radiators and heater cores. Antifreeze contains corrosion inhibitors and water pump lubricant. That's why we replace it every two years.
Tuesday, March 31st, 2015 AT 9:18 PM