Wsmith1118

Okay so I recently purchased a 2001 A4 1.8TQM engine code AWM. Timing belt and water pump done about 20k miles ago.
When I first got it, the car would not get hot at all so I attributed that to a thermostat stuck open. I changed the thermostat, along with the housing, coolant temp sensor, coolant flange, expansion tank and cap. After, the car began to heat up.l and I saw no leaks anywhere. Everything seemed normal until I began to drive. The car would get slightly hot, maybe 1 line past halfway. I then tried to bleed the system thinking there was air in it. The same thing happened again. The engine seemed really hot to the touch as did the upper radiator hose. However the lower radiator hose was ice cold. I even unbolted the housing and let the antifreeze come out and it was ice cold. I then took out the thermostat and the antifreeze on that side was very very hot. So, I'm thinking, the thermostat isn't opening right? So I deemed that the thermostat was defective (since I bought it from Autozone), and went to the dealership and got an OEM thermostat. Now the temp gauge doesn't go past halfway, but the lower radiator hose still seems cold. I opened the expnansion tank cap just a short time ago and it started bubbling out. (FYI, I only have straight water in the system for now as I did not want to keep wasting money on antifreeze until I figured this out. I'm thinking that the bubbling I just talked about is the system boiling over because of no coolant movement so everything sitting in the engine block just boiled over. But the temp gauge never went past halfway!?!? WTF!)

As for now, I'm left thinking
1. Air in the system
2. Bad water pump that isn't flowing (but the car never overheated with the original thermostat that was stuck open....)
3. Is it possible that I got two defective thermostats with the second even being OEM? Yes I tested them and they opened in boiling water.
4. Do I want to set this car on fire and watch it burn? Lol

I'm at a loss for words as to whats going on. I've done a thermostat on my last B5 and had no problems. Also, the Aux fan (passenger side) does not ever come on, not even when I turn on the a/c. I'm assuming that since the lower radiator hose is cold (where the aux fan switch is located), that is obviously why.

Also, after assuming the first thermostat was defective, I put the original thermostat that was stuck open back in and everything went back to how it was originally (never heats up).

Or am I crazy and nothing is wrong at all and the lower radiator hose just stays cold?

fuzzyl

Hey I recently got an 2001 A4 Quattro 1.8t AWM myself and I've recently installed the FMIC, downpipe, forged DV, 2.0 coil conv. kit.. and the very next day it was over heating that's where I went through exactly what you did in trying to bleed the system over and over thinking it's got to be air locked.. I even flushed my heater core and it was barely dirty at all to my surprise, the lower radiator hose was never getting hot and my coolant was boiling over in the reservoir. I changed thermostat, ect sensor.. same problem.. I removed the thermostat and ran without one, same problem. I then removed the thermostat and stuck my finger into there and felt the broken fins on the water pump. This is what I found and I'm currently 3 hours into replacing the timing belt with a gates racing and all metal water pump. I would pull the thermostat and check your fans.. the stock ones are plastic mine were shattered. Here's some pics.

fuzzyl

Let me know what you feel when you finger the thermostat hole I really hope you got a all metal water pump when they changed it 20k ago.. if not highly suggest you invest in it.. the tbelt is kinda fun to do on this vehicle removing the whole front bumper with most of the stuff attached to it takes all of maybe an hour and then the fun begins.. while your in there is a nice time to address any other issues.. I did my ps pump in a couple minutes inbetween doing the timing belt.. it's all installed and ready for the front end to go back on after 3 hours and that's with a new valve cover and double checking tdc removing plug1.. I did end up breaking my AC bracket which I found on ebay for 20 bucks shipped luckily so i'll be doing that once it arrive but can do that from under the car no prob.

David.Norton

The coolant boiling over when you opened the cap is normal, it needs pressure to keep from boiling. If you can drive it without the temperature gauge going over half way then you are working correctly. These engines don't make a lot of heat while idling, the thermostat is going to keep it in the block, and with the engine fan drawing air though the radiator the radiator will stay cool. So I would suggest you put your OEM part back in and take it for a short drive. If it stays at the center you are good to go, if it tries to overheat then limp it back home. That is the nice thing about not making a lot of heat on idle, you can get it home without damage as long as you take it real easy. Also, when you fill the system be sure to keep it below the max fill level on the expansion tank, if you overfill something is going to break when you heat it up.

Wsmith1118

I have driven the car yesterday and today and the temp guage has stated right where it should be in the middle. I understand the lower hose would be cooler after going through the rad but it just seems weird that the lower hose would be ice cold even after I beat on it a little. As for the water pump, I'm not sure if a water pump with a metal impeller was used. I'll have to check that.

fuzzyl

Yeah true but if you' don't have the cap on to begin with and let it idle for about 20-30 minutes it will start boiling in the reservoir which is all pointing towards a broken water pump... he just needs to take 10 minutes, a 1/4'' ratchet and extension and a 10mm socket pull the thermostat out and stick a finger in there to feel his destroyed water pump.. simple

fuzzyl

So WSmith1118 did you check the water pump impeller blades yet? If you did and it's not them I'd say it's less common but still possible that there's a blockage in your heater core and the flow is being so restricted that there is barely any flow.. luckily this is probably the easiest car to do a heater core flush on. The lines are right next to the battery, get a couple of 3/4'' tubing about 3-4 ft long from hardware store and some hose clamps... move the clamps off the heater core lines and pull them both off.. connect a 3/4'' tubing to both of the heater core lines and run your garden hose starting on low on either side of the tubing you installed, flush it with garden hose water until it's flowing out clean and clear from the opposite 3/4'' hose you installed (have it running over your fender or into a bucket). Then reverse the water flow and flush the reverse direction. Like I said though.. I doubt your problem is a heater core or blockage, this is text book water pump issues.

twentysevenlitres

Don't know about overfilling breaking something... The system will normally just push coolant out through the pressure cap as it expands, and when it cools back down it will be around the Min mark somewhere.
Do agree it's pointless to overfill.

The Aux fan should also operate at regular intervals when the aircon is on. This happens independent of the thermoswitch in the bottom of the radiator, which is a two stage switch to operate the fan regardless of aircon on or off. Extreme cold may inhibit operation of aircon which will affect fan operation.

Did you replace the expansion tank?
It's always worth checking as they crack easily - especially on the narrow filler neck under the pressure cap.

David.Norton

I had overfilled (the tank was old and I couldn't see the marks), and the hoses being old split to save the cap releasing. I did it twice, took two hoses one at a time, a very irritating day. Clearly I was being my own worst enemy. Anyway, I mention it because our cars are getting old (I learned this on a 5000), and we could start having this issue.

ringsonfire

I'm having the same problem except I replaced the water pump, timing belt, thermostat and housing. I thought it was until when I was doing the happy dance because the temp gauge was right in the middle, then I turned on my heater-cold air wtf!. Then temp gauge made a bee line for hot. When I got home I did notice a very small leak but the thermostat housing but when I shut it off I pulled the bottom hose from the heater core and nothing came out. When I changed the water pump I flushed the heater core out and there is no blockage. Anyone???