This is my first time DIY post. please be gentle...
So a couple weeks ago I was on the highway and I noticed my coolant temperature was much lower than normal. The normal gauge indication is halfway but I was seeing 1/4. Then when I went into the city and was driving at slower speeds the coolant temperature went up to around the normal value. Immediately I was thinking (and hoping) thermostat because of the symptoms. Next day I started the car and held the upper rad hose while the car ran from a cold start. The hose heated up slowly proving me it's probably the thermostat. Later that day I also got a check engine light. P2181, my coolant temperature is not at the expected value....which makes sense given the situation.
Reading through the forums I saw that people were getting quoted 5 hours of labor for a thermostat fix at the dealership. With the labor and parts this would run over $1000. I futher kept searching through the forums and I came across an article where user ClubSport described how he did have success in the replacement by himself. This lead me to give it a shot and try it out.
I got the thermostat at the dealer because I was not willing to wait for an online order. I also live in Canada so it would probably cost extra for shipping and duty. Those living in the states and who have time to wait, I suggest ordering it from a number of online parts sites. Around $80 for the part. I ended up paying $200CAD at the dealer. Also, the thermostat is an assembly part. It comes together with the housing and you replace both at the same time.
I will now go into the process:
Parts and stuff required:
1. Thermostat assembly ~$200 (Includes thermostat, housing, and gasket. DON'T buy extra gasket, it is already included)
2. 4L Audi Antifreeze: $30
3. screw type hose clamps: $3 (optional but greatly recommended, will cover later)
4. 4L Distilled Water: $2
Step 1: Drain Coolant
I did not completely drain my system of coolant, only what came out of the drain plug. I needed the full 4L of antifreeze and another 4L of water upon refilling. So if you want to do a full flush, naturally you will need more coolant/antifreeze.
Remove the skid plate underneath the car as per an oil change. Locate the thermostat housing assembly next to the oil pan on the drivers side of the car.
The above image shows the coolant drain plug which is located on the thermostat assembly itself. It is a plastic screw which can simply be unscrewed with a phillips screwdriver.
Step 2: Remove lower rad hose and sensor wire
The wire connector is simple to remove, just a regular electrical connector. The hose clamps though are not fun. They require a set of pliers and a massive pain I found to get off
. Once removed, move it aside to give you more room as shown below:
Step 3: Removing the 5 bolts holding the assembly in place
These bolts are an invert torx bolt which are all relatively easy to get to except one. The lowest one is right above the oil pan and it is basically impossible to get any type of socket bit on it. What I was able to do though was that these are conveniently the same size as a 1/4" socket so I used a small 1/4" wrench to get it undone. These bolts are tightened to 9Nm, so I was not worried about stripping the tops. I loosened the rest of the bolts with two extensions on a 1/4" socket wrench.
Step 4: Remove coolant tank hose
Now that the thermostat is free to move I found I had to move it around and rotate it quite a bit to get a good hold on the clamp holding it. Once this is removed the old thermostat is out.
If you are curious, when i pulled the thermostat it didn't look stuck open until i looked inside the assembly and there was clearly a gap as shown below.
The below image is the new thermostat perfectly sealed:
And this is what the assembly looks like:
Step 5: Installing new thermostat assembly
Make sure the surface of the coolant pump housing is clean to ensure a proper seal:
Simply reinstall the bolts the same way with 9Nm torque on each. I was not able to use my torque wrench obviously on the one which needed the wrench. Instead I compared the amount of force required to unscrew an already torqued bolt with the same wrench and relate it to the bottom bolt in force needed to tighten it. Yeah I know, not too sophisticated but it got done...
Step 6: Reinstall hoses and electrical connector
I suggest replacing the OEM clamps with screw type clams to make future repair easier. Like what I am showing below:
Step 7: Refill Antifreeze/Water mixture
Like I said earlier, I needed the full 4L of antifreeze plus another 4 L of water to refill my system. I only drained the coolant from the actual drain plug and not the entire system, thus you will need more coolant if you do an entire flush.
Step 8: Run, and check for leaks
Overall this job isn't too bad. There are some tight spots and a hydraulic lift is definitely a nice thing to have to make your life easier. The worst part for me were the hose clamps, but in future that wont be an issue with the ones I replaced them with. The job was approx 2 hours from start to finish.
I hope this writeup will help those interested in doing this replacement and if you have any questions please let me know. Below is the reference I used to find the torque specs for the bolts and also, this is a great resource to see the blown up view of the entire system. Good luck all!
Ref:Audi Workshop Manuals > S5 Quattro Coupe V8-4.2L (CAUA) (2009) > Engine, Cooling and Exhaust > Cooling System > Thermostat, Engine Cooling > Component Information > Service and Repair > Coolant Pump and Coolant Thermostat Assembly Overview