Beginning work on coolant expansion tank post

Author: mattpopovich

_posts/2026-xx-xx-how-to-replace-coolant-expansion-tank-audi-a3-s3-vw-golf.md

@@ -0,0 +1,121 @@
+---
+title: "How to Replace the Coolant Expansion Tank And Cap for Audi A3/S3 / VW Golf"
+author: matt_popovich           # Reference author_id in _data/authors.yml
+# Can also use `authors: [<author1_id>, <author2_id>]` for multiple entries
+date: 2026-08-05 16:38:29 -0600
+categories: [Blog, YouTube]    # <=2 values here: top category and sub category
+tags: [audi, audi a3, volkswagen, vw, how to, tutorial, youtube, coolant]                # TAG names should always be lowercase
+layout: post                # post is the default, we will set it to be explicit
+pin: false
+toc: true                   # Table of contents
+comments: true              # Enable/disable comments at the bottom of the post
+math: false                 # Disabled by default for performance reasons
+mermaid: false              # Diagram generation tool via ```mermaid [...]```
+#img_cdn: https://cdn.com
+#media_subpath: /img/path/
+image:
+  # path: /assets/img/posts/2026-xx-xx-TODO
+  # width: 1200   # in pixels
+  # height: 630   # in pixels, 1.90:1 desired by chirpy
+  alt: TODO
+  show_image_in_post: false
+description: How to replace the coolant expansion tank, cap, and which coolant to use!
+---
+
+<!-- {% include embed/youtube.html id='TODO' %} -->
+
+## Intro
+Hey guys! Matt Popovich here. Today in my [series of Audi posts](/tags/audi/), I'm going to show you how to replace the coolant expansion tank. This is a fairly common location for coolant to leak as the car gets older. This is a fairly simple fix with minimal tools required. I will be demonstrating on a 2015 Audi A3 but the procedure will likely be the same for Audi S3, VW Golf, VW Golf GTI, VW Golf R, and things will be similar for many other Audi and Volkswagen models.
+
+
+## [TL;DR](https://www.merriam-webster.com/dictionary/TL%3BDR)
+1. Optional: Flush coolant system
+  - Fill with distilled water, run vehicle, drain by disconnecting lower radiator hose.
+    - Or use a vacuum system
+  - Repeat as desired
+  - Draining coolant without a vacuum system will introduce air into the coolant system. After refilling, the coolant will appear "full" but the system will contain air and coolant. After running the vehicle, the system will bleed air out of the system and the system will be low on coolant. It will likely require a few "top ups" before the system is fully bled of air and the air is replaced with coolant. Keep a close eye on the coolant level after flushing the system without a vacuum.
+1. Disconnect and remove the coolant expansion tank
+  - Coolant level sensor + 2 clips (bottom) + 2 coolant hoses
+1. Purchase new coolant expansion tank + coolant expansion tank cap/lid
+1. Install new coolant expansion tank + coolant expansion tank cap/lid
+1. Fill coolant system up such that the final ratio is a 50/50 mix of coolant and distilled water.
+  - If you flushed system with distilled water, add coolant concentrate. Otherwise, continue to add a 50/50 mix.
+  - G13 coolant has been discontinued and replaced with G12evo (Valvoline HT-12). Both are compatible with each other and compatible with most of Audi's older coolants (such as G12++ aka Valvoline G40).
+  - Use refractometer on coolant from the coolant expansion tank after running the vehicle to estimate the current dilution.
+
+## Identifying the Problem
+Low coolant does not mean that the coolant expansion tank or expansion tank lid / cap have gone bad. There are plenty of places in the engine that coolant moves through and could be leaking 🙃
+
+If you are unsure where the leak is, I would start by removing the under tray / shield, rinsing the engine bay (hose is fine at low pressure or dumping buckets of water), letting it dry, top the system up with coolant, *look for leaks*, start the engine, *look for leaks*, apply throttle, *look for leaks*, go for a drive, *look for leaks*.
+
+> A more *professional* way of looking for leaks would be to get a [coolant pressure tester](https://amzn.to/4idtmtr) to pressurize the system to ~15PSI, which is effectively the same as running the engine - only with a pressure tester, the coolant isn't getting scalding hot!
+{: .prompt-info }
+
+If you still don't see anything, the leak might be miniscule (and maybe you can live with continually topping off coolant?). It might be helpful to get a flashlight, ultraviolet light, or maybe even some UV coolant additive to help the coolant stand out with the ultraviolet light.
+
+For me, the whole system looked pretty good after topping off with coolant and having the vehicle idle. It wasn't until I added throttle that increased pressure in the coolant system and caused coolant to start leaking everywhere.
+
+When lots of coolant is leaking, go to the highest point as that is where the leak started.
+
+> My timeline of coolant leaks started with my water pump / water pump union was leaking, then I had a random coolant hose that was leaking, then the coolant expansion tank / cap went bad (158k mi, 254k km). 🫠 🫠 🫠
+{: .prompt-info }
+
+## Fixing the Problem
+
+### Removing the Coolant Expansion Tank
+If you identify coolant leaking near / around the expansion tank, a good place to start is by replacing that. It might not be the exact problem that we are looking for, but the goal is to eliminate *possible* problems one by one.
+
+> If, when attempting to add coolant to the coolant expansion tank, if you miss and add some coolant around the "lip" of the expansion tank, it will immediately drain to the passenger side of the expansion tank. Do not mistake this as your coolant expansion tank being faulty. This is just a skill problem on your part ;)
+{: .prompt-info }
+
+To remove the coolant expansion tank, you must first wait until the car is cold. This will take at least a few hours and ideally overnight.
+
+If the coolant expansion tank has coolant in it, you can either attempt to remove that with a baster (TODO: sp?) or you can plan on making a mess whenever you remove the coolant tubes from the coolant expansion tank.
+
+Start by removing the coolant level sensor. You can squeeze the tab and pull it out, but it's normally much easier to use a [pick tool](TODO link to on amazon) to release the tab and then pull it out.
+
+Next, I found it was easiest to remove the bottom two tabs below the coolant expansion tank by pinching them and then pulling the expansion tank up. Do one of them at a time.
+
+Lastly, remove the clips / rings from the two coolant tubes connected to the coolant expansion tank. You can leave them close by, or, I typically slide them up the tubes and leave them there so I don't get them mixed up.
+
+That's it! Your coolant expansion tank should now be removed.
+
+### Installing the New Coolant Expansion Tank
+
+You might as well replace both the expansion tank and the cap at the same time as the cap is not much more expensive.
+
+Cap:
+
+
+Tank:
+
+### Refilling with Coolant
+
+
+
+
+
+## Outro
+That's it! You're now one step closer to being a certified mechanic! 🧑‍🔧
+
+Please let me know if this was helpful or if you had any questions or issues in the comments.
+
+&nbsp;
+
+<div style="text-align:center">
+<iframe
+style="border-radius:12px"
+src="https://open.spotify.com/embed/track/6rDUuoY74LZ8c8T8hcybIQ?utm_source=generator"
+width="80%" height="352" frameBorder="0"
+allowfullscreen=""
+allow="autoplay; clipboard-write; encrypted-media; fullscreen; picture-in-picture"
+loading="lazy">
+</iframe>
+</div>
+
+&nbsp;
+
+<small><small>
+Disclaimer:
+Matt Popovich is not a mechanic. Please do your own research and consult with a professional before attempting any DIY repairs. Matt Popovich assumes no liability for property damage or injury incurred as a result of any of the information contained in this post. Matt Popovich does not provide a warranty for any of the listed information and does not guarantee any expressed or implied result. Use this information at your own risk. Matt Popovich recommends safe practices when working on vehicles and or with tools seen or implied in this post. Any injury, damage, or loss that may result from improper use of these tools, equipment, or from the information contained in this post is the sole responsibility of the user and not Matt Popovich.
+</small></small>