DIY: S5 4.2 Thermostat replacement Step by Step - Audi A5 Forum & Audi S5 Forum
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post #1 of 33 Old 14th September 2014, 04:54 PM Thread Starter
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DIY: S5 4.2 Thermostat replacement Step by Step

Hi all,

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

-Chubz

Last edited by chubz425; 19th October 2017 at 07:42 PM. Reason: Photobucket pics didn't work anymore
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post #2 of 33 Old 23rd September 2014, 10:50 AM
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Great post, I need to do it next weekend on my S5. Looks like thermostat is another problem of this engine...

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post #3 of 33 Old 24th September 2014, 03:56 PM Thread Starter
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Hope it helps! It's nothing too cosmic so I'm sure you'll have no issues. I know the V6T got a recall for thermostats. Maybe our engines suffer from the same supplier as those but with mo recall
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post #4 of 33 Old 29th September 2014, 06:42 AM
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I changed it on Saturday, 5 hours, but now temperature is back in normal values like 105 C deg, for oil, 90 C deg for water, which means 105 C deg in normal drive and 90 C deg for full throttle.
Consumption is back in "normal" values too.

Your post was really helpfull, thanks again.

Even for Europe, or for metric system, I used little bit "upgraded" key 6 for this one problematic bolt.

I have Elsawin, but it says, no problem just unscrew all 5 bolts...
I would like to see the author how he would do it...

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post #5 of 33 Old 29th September 2014, 03:34 PM Thread Starter
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Nice I'm glad it helped and you were successful in the fix!!
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post #6 of 33 Old 17th July 2015, 10:13 AM
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After 10 months, I need change it again, because temperature is too high now, water is 118 C deg and oil 125 C deg in highway speed.

I hope it's not water pump now.

Good thing is, I did change this problematic bolt for new one with metric head nr. 10, so it was much easier to unsrew it.

Now it was just 3 hours...

I have found, You can see directly to thermostat if You put down a left air guide grill, see picture.
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Last edited by C99; 19th July 2015 at 07:06 AM.
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post #7 of 33 Old 18th July 2015, 06:15 PM
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Great writeup!

2012 Audi S5--red
2000 Integra Type-R
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post #8 of 33 Old 11th August 2015, 09:29 AM
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For a first post...well done!!
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post #9 of 33 Old 4th February 2016, 03:34 AM
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This thread saved me! +1 for folding up and away the drive side fender lining to get a better vantage point of the thermostat!
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post #10 of 33 Old 5th August 2016, 05:03 AM
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Hi there,

So thank you for the DIY thermostat replacement on the 4.2L V8 S5. I went under my car last night to do this and found my configuration a bit different from yours. Specifically, I have another hose passing under the rad hose and it appears to be limiting my access to the thermostat even further. Any idea what this hose is and has anyone had to replace their thermostat with that hose present?

See image below:


Last edited by pdxr; 5th August 2016 at 05:03 AM. Reason: missing image
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post #11 of 33 Old 6th August 2016, 07:58 PM
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Well, I managed to get my rad hose off the thermostat, but ran into a new little issue - 4 of my bolts holding the thermostat look exactly like this DIY shows, but the 5th - the hard one just above the oil pan - looks like this:



So I'm at a loss as to how to deal with this fairly inaccessible bolt. Any ideas?

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post #12 of 33 Old 8th August 2016, 07:40 AM Thread Starter
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Almost looks like an XZN socket head looking at the picture... If so, I'm sure you can get a small Alen key set with XZN rather than HEX. Any luck or getting it undone? Any other ideas?
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post #13 of 33 Old 8th August 2016, 12:44 PM
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I bought a flexible screw driver shaft today...going to try that tonight. It's my only option. There are too many pipes above to get a ratchet in there with an appropriate bit.

I will let you know how things go tonight. If this doesn't work though, I'm at wits end and tempted to go yell at my dealership. Given this is the first time I'm looking at the thermostat and they never replaced it with my knowledge, I have no clue how this single bolt could've gotten all scratched up and be completely different from the other 4. It seems highly unlikely to me that this one was put in at the factory.
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post #14 of 33 Old 11th August 2016, 08:04 PM
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Quote:
Originally Posted by pdxr View Post
I bought a flexible screw driver shaft today...going to try that tonight. It's my only option. There are too many pipes above to get a ratchet in there with an appropriate bit.

I will let you know how things go tonight. If this doesn't work though, I'm at wits end and tempted to go yell at my dealership. Given this is the first time I'm looking at the thermostat and they never replaced it with my knowledge, I have no clue how this single bolt could've gotten all scratched up and be completely different from the other 4. It seems highly unlikely to me that this one was put in at the factory.
No dice. Had someone suggest I lightly hammer the bit in at an angle to help get me grip and spray the bolt with WD40 or something similar.

Any other ideas before I commit to one?
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post #15 of 33 Old 5th September 2016, 07:48 AM
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HI pdxr, I have not changed my Thermostat (yet) so I can't tell exactly what is in the way; other than the oil pan comments. Changing oil, coolant, and in this case thermostats are the "gateway drugs" to more advanced wrenching so don't give up!!

Fortunately, the bolt is not very tight (hopefully) and perhaps you could get a very small needle nose vice grip pliers on it . If you can't access the head with the vice grip, you may have to get some help by having the beaks of the needle nose vg's warmed with a torch and then bent slightly in a "J" configuration. You may then have the proper reach. They do sell needle nose pliers in this configuration, but you won't have the extra grip provided by the vise-grip feature.

Hope that prompts some thought for you and the others reading your challenge ; don't give in, you'll get it.

Stefan
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post #16 of 33 Old 5th September 2016, 09:59 AM
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I see now what you mean: photo five from the top. Its a bit of a reach!


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post #17 of 33 Old 5th September 2016, 10:19 AM
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You could also get allen tips (metric and sae) or torques tips and try to get one in the site that fits very tightly; you will have to wiggle it by hand until it seats all the way down in the site. Be patient, as this will take some trial and error. Seating it in all the way will be the key so you can apply some torque to the bolt. Stefan

I tried to post some pics, but no luck.....yet.
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well, not like the beauties (pics) from most of you, but its a start!
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post #23 of 33 Old 11th October 2016, 01:19 PM
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hello all, I'm doing my stat this weekend and was trying to figure out for the 5 mount bolts what size is the invert torx socket, i saw another guy on here said it was a torx 30 but i can find one anywhere and it seems really big anyone know?

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post #24 of 33 Old 13th January 2017, 10:32 AM
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I did this job this weekend in my garage on jack stands, and I wanted to say thank you to @chubz425 for this excellent tutorial! I followed step by step and it was a life saver! I also had the front bumper cover off too, as I was changing out my grill for an RS5 style one at the same time, and that gave me some more access.

As mentioned, the hardest part for me was that hose clamp, as access is really restricted. After my vice grips wasn't doing the job, I went and got a special tool thats used to clamp the hose clamp open, and then I could push it off. The other issue as mentioned was the bottom bolt, and I did end up using the 12 pt 1/4" wrench, a small turn at a time. Putting it all back together again was a lot easier and now my car is running back to normal operation temps.

Matt
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post #25 of 33 Old 4th April 2017, 12:34 AM
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Wow, you weren't kidding about the hoses. After 5 hours, I gave up as I couldn't get the top hose off the tstat (the one that connects to the upper coolant pipe, not the lower radiator hose). Got coolant in my mouth and eyes, and struggled even with the drain plug (such malleable plastic), and the bolt under the drain pan (finally got it off with small baby steps). Got the car towed to a mechanic who finished the job for me. First time I've failed a repair

The engineers who designed the location of this thermostat must've absolutely hated mechanics. On better news, car is running MUCH better now. Radiator fan isn't blasting, didn't see the needle rise, and the ECU says it's around 95-105C (had the ECT sensor replaced as well, and today was a cold one, so can't 100% confirm the tstat was the issue).

'08 S5 6MT
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good
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post #27 of 33 Old 4th April 2017, 01:24 AM
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i think its trustworthy
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post #28 of 33 Old 4th April 2017, 01:58 AM
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Brilliant write up so thanks!!!! Luckily it seems (so far) that the 3.2 FSI does not suffer from thermostat problems as far as I know???????. Mine runs always at 90 degrees....

Simon
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post #29 of 33 Old 19th October 2017, 07:36 PM Thread Starter
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All,

Was given a heads up that the photos weren't working...should be all fixed, but let me know otherwise. Thanks and glad this is helping people!!
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post #30 of 33 Old 16th April 2018, 01:09 PM
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I have played with the VCDS and I have noticed the 'Thermostat Duty Cycle' group.

Is it rly the thermostat data?
If so mine looks weird... Coolant temp 90-95deg and it shows 13-90% ...
Is it normal, isn't it?

My coolant boiled once and still do not know what happened


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