Number48

A quick write up on a slow overheat issue solved by a thermostat replacement.
Problem
When I purchased my D2 a couple months ago, I didn't realize it was going to be as much of a project as it is. However, I have the skills and tools to do just about anything for repairs. One of the issues I didn't realize I had until I bought it and drove it home was a slow overheating issue (my first ride home was 30 minutes of regret). Aside from the power steering leak (replaced the rack later), the high temp was not disclosed upon purchase. Of course, my first thought is what if it has bad head gaskets. So I took a deep breath and took a logical approach and start with the easiest first. The car wouldn't get hotter than last fat white gauge mark, and would settle down to about 3/4 temp if I put the heat on full blast. Luckily this was still winter here in MN. I could drive it 15 minutes at slower speeds and it would stay below 1/2 on the gauge. Then it would slowly climb up.

Attempted quick fixes
My first approach was a coolant backflush at a shop, to no avail. Then I used a pressure washer to blast through the A/C condenser and radiator fins in case there was debris/fuzz buildup (I have seen this before in other cars). Next, while purchasing a used wheel/tire to replace the spare that wasn't there, the seller informed me he had the same issue on his A6 (4.2 L) and his solution was the timing belt wasn't tight enough to turn the water pump impeller properly. So I checked that, and the timing belt did seem a bit loose. But no luck, so I ordered a new thermostat and gasket from Rock Auto. Thanks to this forum and youtube, I was able to replace the thermostat and sneak it past the timing belt without removing the belt. I put it back together and wouldn't you know, it runs just below half all the time and now I don't have to sweat my *** off driving it.

Repair
Here's the steps I took to replace my thermostat:
-Removed the timing belt covers
-Removed the viscous fan (remember the fan is opposite thread-lefty tighty, righty loosey), loosened the serpentine belt but didn't fully remove, then removed the fan pulley
-Disconnected the upper radiator hose at the radiator and pushed aside.
-Disconnected the lower radiator hose from the upper location but left connected on the radiator
-Loosened the timing belt and installed zip ties to the cams
At this point, the timing belt is exposed, and I turned the engine over by hand until the upper circuit between the cams was a little slack and the cams didn't feel like they wanted to spring forward or backward. I marked the timing belt and cam sprockets. Then I installed 2 zip ties on each cam to make sure the timing belt wasn't going to slip off the sprockets. I installed them a little loose to allow the belt to slide forward a little bit, but not come off. I loosened the eccentric timing belt tensioner to allow the tensionser to rotate and create more slack in the belt.
-Removed the 3 bolts on the thermostat housing
-Removed the bolt holding on the vacuum solenoid on the front of the intake to allow for more room to remove the thermostat
-Remove the timing belt upper idler pulley
-This was the tricky part, I was able to pull the thermostat housing forward up against the timing belt, twisting the belt to allow for more room, then I sneaked the gasket and thermostat through the gap on the top, gently twisting the thermostat to get it through. Make sure you are monitoring the timing belt on the cams, I was putting a lot of trust in the zip ties. And voila! It was out.
-Since some coolant inevitably will get on the timing belt, I used some clean water and poured it down the hole. Maybe this is frowned upon, but my attempt to keep coolant off the timing belt failed, so I took the chance. I used some compressed air and blew that down the timing belt area to help dry it out a little more.
-Reverse procedure to install, fill it up and give it a burp

I hope this helps anybody trying to tackle a thermostat replacement without a full timing belt replacement. It was a risk I was willing to take.