One problem after another! I still have not resolved the CEL issue with my oxygen sensors (b1s1/b2s1) and here it is… something is leaking… my coolant.

I am noticing coolant spots under the car since last week, but I really wanted to resolve the CEL problem before introducing this one.

The interesting thing is that the coolant does not leak constantly. I drive to work (10 miles) in the morning and at the end of the day I see large spot of coolant. So, I fill up the reservoir with 50/50 solution until the next day. But this is crazy, and I really want to fix this leak and do a flush.

I can not find any cracked hoses. Is there a valve, which will let out coolant if the pressure is too high?

 

The cap has a built in pressure release valve if your overheating, but that's not likely the problem. There are two common problems. Cracks in the reservoir that slowly seap out. If it looks cracked replace it. Second, under the intake manifold is the auxiliary coolant pump.Look past your DV's toward the center and look at the outlet for the pump. You will probably see a crust around there that is caused by a slow leak. That one's a bitch to replace or repair.

 

I own a 2002 A-3 that also has a mysterious antifreeze leak that the dealer cannot find. Did you resolve your problem?

 

aux water pump. very hard to see

 

I had a crack on the bottom of my res that could not be seen until i took it off. for under $20 i would start with the res.

 

I seccond the aux water pump. I had the same issue and I hear they are prone to leaks.

 

look under the hood. do you see anything signs of leaks on top. with coolant leaks in hoses, you wont be able to see the leak, unless its hot and leaking at the time. if you dont see anything, start small like said above...

 

it will be the water pump ( only time you see it is when the engine is off ) the system normaly drops pressure through the cap as already stated, engine running coolant is on the move so dosnt leak from the water pump because the fan cuts in to releave the pressure so on short runs it dosnt get hot enough to do that and thats when you see the puddle on the floor.

edit: just one point and a common one indeed is the V6 tends to leak coolant under the plenuim but that tends to dry up quick with the heat of the engine so you rarely see coolant on the floor

 

over the past few months i noticed small drops of coolent under my car in the garage nothing big no puddles or anything. when i did a timing belt on my car i noticed the water pump was leaking out of the weep hole which i replaced. but as i was looking around and noticed under the intake i could see the aux coolent pump had been leeking. there was dried pink residue around the hoses and a small drip as well. so if you have just a small drip take a look at those two places.

 

Res. tank cracks can be hard to find. If your really having trouble with your sensors. replace them, just do all four if you have to.

I would say.

-Do the o2 sensors.
-Flush coolant.
-Do Cam belt/water pump/thermostat
-Replace res. tank.

I am almost certain it will be your water pump/thermostat. How many miles do you have on the car?