We purchased the car in November with 78.000 miles on it. The car cad cooling problems at the time of purchase. The PO had replaced the thermostat but the fans did not run. We bought fans from Indytom and they worked A1. Still overheated and we did the timing belt along with a new water pump from NAPA. The old impeller was in two halves. The egine code is BDC 2.0.......Yes to your question of G12, we use it, just not prepared to install untill we are stable.You said that the water pump was replaced 3 months ago. Where did you have it replaced? What is the history of the car? How long have you owned it and have you had any other cooling-related problems? Have you always used VW G12 coolant?
I believe that I heard that there is an identical water pump to the one in the 2.0 except that is designed to turn in the opposite direction. Apparently some other engine used the same pump but a different belt arrangement. Maybe you got the wrong pump in there and it hasn't caused problems until the weather warmed up.
A suggestion for filling the cooling system: remove the topmost hose to the heater from the cooling flange when filling the system. Once the water level reaches the flange replace the hose. This will allow the air to escape as the system is filled. If you have it filled with water now, you could crack the connection (with the engine cold) to see if you can burp any air out.
Thanks for comfirming the water flow direction, I will double check the pump with NAPA for fitment, we have the receipt.Coolant flange is the proper name for the "plastic heart fitting." I'm suggesting using the heater hose that starts there as an air bleed.
The coolant flow pattern is in through the lower radiator hose and the thermostat to the pump, from there into the block and then up to the cylinder head, out through the coolant flange and to the upper radiator hose.
The water pump from NAPA should be OK. Do you have a record of the part number that you bought? You could double-check the application for it and make sure you got the right one.
You mention boiling in the coolant reservoir. There really shouldn't be bubbles coming out there. Do you see an unusual amount of steam in the exhaust when the boiling happens? It is possible you have a blown cylinder head gasket that keeps air in the system and doesn't allow coolant to flow out into the upper radiator hose.
Yes, I really do appreciate the extra "how to", I am a rookie.The recommended procedure for filling the cooling system is to fill to the mark on the overflow tank, put the cap on tight, idle the engine until the level is a the bottom of the overflow tank, shut off the engine and cool as needed to remove the cap, refill and repeat until the level holds.
Running just water may make the cooling system behave a little different than normal since it will boil at a much lower temperature, around the point where the cooling fans should be kicking on if you don't have the cap on. With the cap on the extra pressure will raise the boiling point some, so that would be preferred. Just be real careful to cool the engine before you remove the cap or the water will begin to boil as the pressure is released.