2009 Hatchback. 96k miles on it. When purchased noticed a grayish color in coolant. Car ran and drove and didnt overheat. Did notice a dripping leak on passenger side of the engine. After further inspection i found a bad water pump that leaked out the weep hole. Replaced some of the coolant system, Tstat housing, water pump and pipe between the two. Bleed system more than once and I get no heat. I bleed again and get heat but then disappears then comes back. I come to a stop at my house and overflow boiling over out of my expansion tank. I wait till it cools and replace the cap with a new one. Seems ok. I drive around and heat at first but then no heat. Stop and no boiling over. I drive again and heat comes and goes. I finally bleed again and buy a new cap, the cap i used was from a parts car i have but ordered one online and thats the one i put on today. I have back flushed the heater core three times. Some stuff comes out but then the heat works when it wants to. I cant figure this out. I do see some oily spots persay on the antifreeze in the tank but not creamy. I even did the blue liquid test three separate times on the car through the expansion tank and never turned yellow.

My ideas are as follows: Cracked block or head that doesnt show itself until hot. Expansion tank has a crack in it I cant see. I did notice that the front fan on the radiator only comes on high at 233 degrees and not slow at a lower temp which might cause the boiling. I have searched lots of forums and cant solve this one.

 

Could your idler not be making good contact with the water pump pulley?

 

I see the water pump pulley spinning so I dont think that is it. But I read below that it could be a low coolant fan issue.

 

It sounds like you have air in the system. First, I'd suggest a pressure check of the system to make sure there are no leaks. Keep in mind cooling system pressure is 13-15 PSI, so don't over pressurize the system.

If you find that the system is holding pressure, fill the expansion tank to the max level, and then start the engine. Let the engine reach operating temperature and then shut it down and let it cool off. The coolant level in the expansion tank should drop; fill the expansion tank to the minimum level and install the cap. Repeat the warm up and cool down cycles until the level in the expansion tank no longer drops when it cools off.

I've heard about the fan low speed issue, but the Bentley service manual states the DME will momentarily run the fan when you start the engine. The DME will compare the fan speed to what's stored in memory, and if the speeds don't match, the DME will set a DTC. I don't recall anything about low speed operation, but I was looking for something about that after my Indy shop told me about the fan's low-speed mode.