I bought an A4 V6 cheaply, not going, and got it going. Unfortunately it is overheating, and it is a bit of a mystery.

The heater core blew out for the previous owner, and he bypassed the heater by joining the heater hoses.

I replaced the water pump, thermostat and timing belt. All were in good working condition, once I'd got them out.

The problem still remains.

I ran hose water through the radiator, through the main block, each of the heater hoses, one of the smaller water hoses at the bottom of the left-hand block. No blockages found yet.

Today I spent time squeezing / burping hoses and getting as much air out as I could, while topping up the water.

I started the engine and as usual there was still no flow from the small return hose at idle or revs.

I put the cap on and warmed up the engine at 1500 rpm. The water temp gauge steadily moved up past 90 to 100 degrees, when I turned the engine off.
The radiator was hot at the top and cold at the bottom. The heater hoses both felt hot, pressurised, and full of water.

The electric fan failed to start.

The exhaust looks normal, there is no fuming from the oil filler, no water in the oil, no oil in the water. There are no steam bubbles in the header tank.
Has anyone ever heard of a blockage in a hose or one of the the cylinder heads?

 

I am a noob to these cars myself, but not to wrenching. I recently have done a complete timing belt service along with a ton of other work to my 01 2.8l. There is some good info around on burping the cooling system. Also temp wise. When fully warmed up my car sits with the needle right at the halfway mark around 200°F. Maybe the car needs to get up to around there for it to circulate properly? I thought I had my system burped after my timing belt service, but not until I got it really up to temp did it start to circulate properly and needed more coolant added. My electric fan on the passenger side doesn't really kick on until warmed up and I put the A/C on. Hope some of this helps.

 

Thanks for that - I'll give it a try. Last night I worked on it til nearly midnight, and after I found a bleed screw back behind the motor in the steel pipe there (in the vee valley), I was getting water coming out of the small return pipe when the engine was running. Temp was around 100 deg C (boiling point for pure unpressurised water) so I wasn't sure if it was the water starting to boil or not.

 

Ohh...100 Celsius is about where I am at with the 200 Fahrenheit. On my '01 2.8l. There is a bleed screw on the front to the right (looking at the car) of the power steering pump. Between that and the timing belt covers. It's a black pipe and the screw is either a 5 or 6mm hex head.

 

I had a good look but couldn't find any other bleed screws so far. 200 F. is 93 C., sounds like pretty close to the ideal operating temp, my gauge just has 90 in the middle (Germans use Centigrade at home) so I imagine that's the temp they are looking for. Do you have a photo you could send me? Today's very gentle test drive (about 2km total) from initial 90 degrees C. saw it steadily climb to 100. So I haven't fixed it yet.

 

Here it is on mine. On my scanner that I leave plugged into the OBDII port to check some sensor data (not a vagcom, that's on the list of things to get). My coolant temp pretty much always reads 204.8 F. Sometimes if hot and running AC it will go to about 208-210F and drop back to 204 when cruising.

 

Some reason that pic is kicked to the left. Needs to be turned to the right.

 

Thanks for the photo. Took me a while to get my head around it, but I recognised the water pump pulley and the fan pulley. I had a really good look all around that area, and it looks like my 1998 2.6L doesn't have this bleed point. In fact, there is no metal pipe there.

I'll do some more research on coolant bleeding proceedure for my model of engine, I reckon air locks are a likely culprit. The small return hose still doesn't return coolant to the header tank.

 

I'm having similar issues. My 1998 2.8L 30v suddenly started overheating and I replaced all the usual suspect components, and still overheating.

BTW,

The 30v front bleed screw is shown here in this photo:

 

Hi and thanks for the photo. Sorry to hear you're having overheating probs, but glad I'm not alone. My car is different from yours - my bleed screw is at the back of the engine, on a similar level. If you hear of anything that sorts your problem out please let me know. I haven't ruled out the possibility of compression escaping from one of the heads and making an air lock - the old trick of looking for steam bubbles in the radiator doesn't work here, as there is no radiator cap, and the header tank comes from the bottom of the radiator.

I'm considering drilling a hole in a big juice bottle and plugging the small return hose into it, filled with water, to see if any steam bubbles are coming up. That's pretty close to the top of the radiator.

I'm waiting for my next trip to town to borrow a compression tester and/or leak down tester to look for obvious compression leakages from one of the cylinders.

I disconnected the 2 heater hoses from where they attach to the heater connections in the firewall and ran hose water through both - each of them makes the header tank overflow, so I assume there are no blockages in the pump's in and out pipes.

Another thing, does your header tank have an overflow tank as well? My header tank overflows directly down onto the exhaust, which is strange.