Check again for the bleed screw at the front. Every 2.8L 30 valve V6 I've ever seen in both Audis and Volkswagon Passats have had both the bleed screw at the front and at the back, plus the weep hole in the heater hose at the heater core nipple. In my experience, all 3 locations need to be bled to get all the air out of the coolant system.

My late production 1998 (after the serial number split point where they changed the plastic coolant tank design) only has the one single tank. My overflow from that tank also blows down the driver's side cylinder bank and exhaust manifold.

I've also looked for bubbles in my coolant and found none. The engine still runs great and makes full power too, so I seriously doubt I have any head gasket problems.

I did check my brand new fan clutch again tonight and when it's over 200 degrees Fahrenheit as measured with a handheld laser thermometer, it slips very freely, and with the engine running and the temps hot enough that it should be engaging much more firmly, I can stop the fan easily with sticking a cardboard paper towel tube into the spinning fan.... that's not right. My brand new fan clutch is definitely a dud. I'm going to reinstall the old clutch to see if it makes a difference. It's a lot stiffer when it's warm than the new clutch.

 

OK, I'll have another search for a 3rd bleed point. Mine's the 2.6L V6, not sure if there are many differences in the water system or not... I can see a straight steel pipe coming straight out of the back of the water pump, down the valley and up into the heater. Does your small return hose to the header tank have coolant flow at revs, even before the thermostat opens?
Yes, that's what I'd be doing with your fan, should be stiffer when up to temps, I remember replacing the gel (a small tube of it was enough) in a similar Toyota fan that was hardly turning when hot.
I can't figure out why my electric fan doesn't kick in when the temp hits boiling point. Any ideas?

 

A 1998 A4 with a 2.6 engine? Is this a non-USA market version? (Europe, Australia, etc)

In 1998 the engine choices for an A4 sold in the US were limited to 1.8L turbocharged 4 cylinder, and the 2.8L 30-valve double overhead cam hemi V-6.

 

There's a 40-amp jumbo-size fuse for the electric fan, hidden underneath the dashboard. Mine was blown and I had to replace it. This is a common thing when your electric fan is in the process of failing. Mine had bad bearings and was squealing real bad, but still turning.... until one day it stopped turning due to the fuse blown.

You have to drop the bottom cover underneath the dashboard (on the driver's side of a lefthand-drive car) and there's another fuse & relay plug-in block hidden under there where that fuse. On a righthand-drive car (UK, Australia, NZ, etc) I don't know which side it would be on.

 

Last night I bypassed my heater core since I know that's blocked, and also replaced the expansion tank since mine had a couple cracks in it that I had epoxied over. It was holding pressure just fine, and not leaking... but my local autoparts store happened to have one in stock (rare to find *any* parts for the Audi in stock there, I usually have to order them over the web) for only $35 and it came with a new cap too, so I bought it and installed it.

Still no real change on my overheating problem. I read an article saying that the aluminum core radiators often loose their efficiency past 15 years old and don't transfer heat as well. Mine's the original, 18 yrs old now. I found a replacement Nissens aftermarket brand radiator at Rock Auto for only $107 shipped, so I ordered it last night and will install it over the July 4th holiday weekend and also put my old fan clutch back in too since the new one never seems to lock up when it gets hot.

For now, I have noticed that the engine reaches normal temperature and the thermostat opens up and stays there at mid-mark on the gauge until the oil temp reaches 225 and then both start climbing. Maybe my oil cooler is clogged also. I'll try flushing it out when I change the radiator.

 

I bought this one in NZ, not sure if it was imported or not.
We drive on the Left, so steering wheels are on the right. Audis and Mercs both forgot to switch the indicators and wipers etc to the correct side when they moved the steering wheels over from left to right. So I'm constantly turning the wipers on when I try to indicate.

 

Thanks, I'll have a look next time I'm out in the garage.

 

Please let me know how you get on. I'm tempted to excavate back down to the thermostat I just put in and remove it to see if I can get some water circulating.

 

I think I've probably just solved mine... I got the new radiator installed and took it for a 15 mile test drive this evening... with the air conditioner running full blast the whole time, the coolant temp gauge never went over one needle width past mid-scale and the oil temp gauge never went past the 200 degree F mark. Now granted, the outside air temps were rather cool for north Texas tonight, but before the radiator change, it ran hot on a similar cool evening drive. I'll know more when I drive it in the heat of the daytime tomorrow, but it's sure looking like the radiator was the main culprit. It would still flow water thru the old one, but must've been partially clogged and internally coated with corrosion that prevented it from efficiently tranferring heat from the coolant running thru it.

 

Hi again, any joy with your overheating probs?
I (briefly) thought my problems were solved - I bled all the places, including the heater hose point as the engine transitioned into the thermostat opening. I revved up to 1500 rpm, got a bit of steam and air out of this bleed point, then it plateaued at 90 c (yay!) for about 4 min, before resuming the climb up into the hundred degree territory and boiling.

I managed to get hold of the dealers' bleed proceedure for this model (ABC motor) and they recommend a tube extension to the header tank to raise the water level high enough to flow out of the heater hose point. Then 2000 rpm for 3 mins to expel any air bubbles. I didn't have the tube, so I used a rag around the garden hose to provide the necessary pressure, I let the water run out of the top bleed point for some time, before sealing it again. Same problem remains...

What crossed my mind was that the radiator fan not coming on was suspicious, and was the radiator partly clogged? (Water runs easily through the radiator using a garden hose) So back to square one...