Green Goo in Radiator

[jcbm3]

I have a 2000 323i (E46 chassis with M52 engine) with 113,000 miles which receives hard highway use and has developed “green goo” in the cooling system.

After changing the hoses, belts and coolant (50/50 mix of BMW Coolant and distilled water) I ran the car for around 1000 miles without properly bleeding the cooling system. Afterwards I noticed “green goo” in the coolant, I believe that the technical term for this goo is “silicate gel precipitation” and that BMW issued a Service Bulletin in 1991 to address this problem (I cannot locate this service bulletin).

I thought the radiator or overflow tank may have been letting air enter the system so I replaced them and this time I properly bled the system. The green goo still persisted. There is also a little “yellow gel” clinging to the bottom of the oil filler cap and the valve cover. Otherwise the car runs fine and the temperature gauge needle is pegged.

My research indicates the goo is usually caused by a bad head gasket. However I just performed a leak-down test and 5 of the 6 cylinders leaked between 10-12% and one cylinder leaked 17%, which all seems to be very good. There were no air bubbles in the coolant, no weird noises, no oil or coolant in the spark plug bores and the plugs all appeared normal. I also changed the oil and it looks fine, not like a “milk shake” and there were no small bits or coolant in the oil filter or housing. There is no white smoke coming from the exhaust pipe, the car idles fine and there is no loss of power. Which leads me to believe that the head gasket is not the problem.

When performing the leak-down test, I noticed some dried coolant on the thermostat housing. Do I need to replace the water pump, thermostat and seals? Is this causing the “green goo”?

Thanks!

[Jeron]

From what I remember, the Green Goo is caused by mixing two different types of coolant.

I would flush the cooling system to get the goo out then start with a fresh load of coolant.

The hard part is going to be getting the system clean. I dont know the best cleaning method to use but I would start with pull both hoses and flush water through the engine and radiator with a garden hose. Then Prestone Super Flush and straight water for a week.