| Is the cooling system stock with original fan? Did it overheat while stopped, or while moving?
If it only overheats when stopped, the fan clutch is suspect. If it overheats when moving, suspect the water pump or a blockage to air flow or water flow. If you use tap water or someone has put radiator stop-leak in it, you could have radiator blockage in the water passages. I once had a radiator with its air fins blocked by several handfulls of cat hair from the long haired cat that lived in my garage. Had to pull the radiator to hose it all out.
I think your car originally had a water pump with a plastic impeller. If so, it is about due for its third water pump. They tend to degrade and crumble about as fast as the plastic radiators (i.e. 7-8 years). If you have a plastic impeller water pump that is more than 7 years old, replace that as a general maintenance item. Also replace the thermostat and examine the thermostat housing for signs of failure while you have it off. Bleed the system carefully and fully when you fill it back up with antifreeze and distilled water. It will overheat if it is not bled completely. I put mine up on ramps so that the radiator is higher than the engine, and then I bleed it slowly and thoroughly to make sure there is no air anywhere in the system, including the heater core.
Don't use 'DexCool' antifreeze, as plastic cooling system parts don't like it. After a couple of radiator failures, I bit the bullet and put Dealer BMW antifreeze in all three of my Bimmers. That was expensive, but no failures since then.  |