Coolant Leak - back of engine area
Thread Starter
AudiWorld Senior Member
Joined: Apr 2009
Posts: 639
Likes: 72
From: Tucson, AZ
Coolant Leak - back of engine area
Hi all, yesterday I noticed a small puddle of coolant under the engine - about even with the back of the front tires, so near the back of the engine. Actually I found 3 separate puddles, each maybe 2-3 oz, So each time, the same small amount of coolant leaked out, and then stopped. Verified it's coolant, because the expansion tank is low. So I cleaned up the puddles, and left the car over night last night with a piece of card board underneath to see how long it takes for the leak to appear. Today after maybe 16 hours that area is still dry.
Some back story - my indy replaced the oil cooler and installed an aluminum Bufkin pipe back in 2019, about 30K miles ago (134K miles today). So I tend to rule out the oil cooler. Have had no other coolant issues since, until this one. I am wondering about cooling hoses around the back of the engine, which I think could be original, or maybe to/from the transmission cooler. I need to get under there and take a look, but asking if anyone has any experience with this kind of leak. Thanks...
Some back story - my indy replaced the oil cooler and installed an aluminum Bufkin pipe back in 2019, about 30K miles ago (134K miles today). So I tend to rule out the oil cooler. Have had no other coolant issues since, until this one. I am wondering about cooling hoses around the back of the engine, which I think could be original, or maybe to/from the transmission cooler. I need to get under there and take a look, but asking if anyone has any experience with this kind of leak. Thanks...
AudiWorld Member
Joined: Sep 2018
Posts: 394
Likes: 54
I would check the line that is under the throttle body. Its the one you need to remove from the intake if you are removing it from the car. This would align with the area you see the leak. If you can get a camera in there you should be able to see coolant in the valley if this is your issue. Otherwise probably something coming from the heater core related hoses or the bleeder valve housing which can crack.
If its on the drivers side mostly, there is a pipe that connects to the engine near the AC unit that is used as an additional drain to get coolant out of the block. Sometimes the connection at the engine will start to leak, usually not too bad though. I think this pipe is in front of the tires more near the center of the engine but the coolant may run along the belly pan and exit around that area where you see the leak. The reservoir itself could have a crack in it too. You could see that clearly if you pull the wheel well and inspect.
Those are the things I can suggest.
If its on the drivers side mostly, there is a pipe that connects to the engine near the AC unit that is used as an additional drain to get coolant out of the block. Sometimes the connection at the engine will start to leak, usually not too bad though. I think this pipe is in front of the tires more near the center of the engine but the coolant may run along the belly pan and exit around that area where you see the leak. The reservoir itself could have a crack in it too. You could see that clearly if you pull the wheel well and inspect.
Those are the things I can suggest.
AudiWorld Member
Joined: Feb 2021
Posts: 119
Likes: 13
My reservoir just burst , and I feel the one on my other car is about to as well. If it’s old and original and you have like 130k miles on original reservoir and cap , just change both.
I noticed alot of d3’s have old caps waiting for failure, you could tell by looking at it . I grabbed a few and pushing around just a bit the inside of the cap just disitingrated . If it looks brown ,or appears brittle, Bingo! . It won’t hold pressure and you’ll have leaks until it finally fails.
I noticed alot of d3’s have old caps waiting for failure, you could tell by looking at it . I grabbed a few and pushing around just a bit the inside of the cap just disitingrated . If it looks brown ,or appears brittle, Bingo! . It won’t hold pressure and you’ll have leaks until it finally fails.
AudiWorld Member
Joined: Oct 2012
Posts: 425
Likes: 51
From: Chicago
drip from back of engine, on top of transmission... I don't know if the non FSI is set up the same, but here was the source of my leak on an 09 FSI...as the same part disintegrates every 6 years or so.
https://www.audiworld.com/forums/a8-...ypass-3060682/
https://www.audiworld.com/forums/a8-...ypass-3060682/
Last edited by Sci-fi_Wasabi; Dec 2, 2024 at 08:41 PM.
Thread Starter
AudiWorld Senior Member
Joined: Apr 2009
Posts: 639
Likes: 72
From: Tucson, AZ
Investigation turned up the source of the leak - from under the coolant reservoir. Good advice, Christian_A, to check the obvious. The original reservoir lasted 15 years/100K miles until it began to crack around the overflow return nipple on top. This one only lasted 34K miles, but the leak is at the point of connection to the coolant level sensor (on the bottom of the reservoir, next to the coolant hose). The sensor is built into the reservoir tank. So new tank ordered, will install next week. At least it wasn't one of those hose connections on the back of the engine!
AudiWorld Member
Joined: Jun 2019
Posts: 439
Likes: 43
From: Houston, TX
I don't get this myself. I am on my 3rd one. My first replacement was even an oem part. It keeps on snapping on the same spot. I think there is too much free play on the hose. Over time the heating and cooling cycle weakens that tiny plastic and it just falls apart.\
Trending Topics
Thread Starter
AudiWorld Senior Member
Joined: Apr 2009
Posts: 639
Likes: 72
From: Tucson, AZ
The small return hose that faces toward the engine? That's where my first one failed. Zip tie that hose to the two nearby brake lines so it doesn't move as much. Otherwise I think you're right, that small plastic fitting can't handle years of hot/cold cycling and the plastic just weakens and (in my case) cracks.
AudiWorld Stories
Bringing Audi to Life for Audi Fans
10 Strangest Audi Designs That Actually Made Production
Joe Kucinski
2027 Audi Q7 and SQ7: Audi Upgraded EVERYTHING!
Michael S. Palmer
Audi Unveils Absurdly Cool New Supercar: 10 Things You Need to Know!
Verdad Gallardo
The Highs & Lows of Every Audi C-Class Generation
Joe Kucinski
Top 10 Most Expensive Audis Ever Sold on Bring-A-Trailer
Brett Foote
10 Audi Features & Options We Miss the Most!
Joe Kucinski
Audi Recreates Crazy-Looking Speed Record Breaker From 1935
Verdad Gallardo
Coachbuilder Recreates the 1995 Audi TTS Concept
Verdad Gallardo
Every Audi V10 Car Ranked!
Joe Kucinski
AudiWorld Member
Joined: Jun 2019
Posts: 439
Likes: 43
From: Houston, TX
There are 2 hvac lines (closest to where it breaks) Mine has this one plastic piece that separates that overflow coolant to the brake line you want to zip tie. I think I may be missing a part because that spacer does not hold the return line firmly in place.
Perhaps zip tie something to the line to make it stiff. Zip tie on 3 points with some insulating spacer in between.
From experience, when 2 line are close to each other, the vibration from the engine causes lines to rub onto each other. This will cause the lines to get damaged.
Last edited by maxandtara; Dec 28, 2024 at 05:50 PM. Reason: add info
AudiWorld Junior Member
Joined: Jul 2002
Posts: 31
Likes: 7
Hi all, yesterday I noticed a small puddle of coolant under the engine - about even with the back of the front tires, so near the back of the engine. Actually I found 3 separate puddles, each maybe 2-3 oz, So each time, the same small amount of coolant leaked out, and then stopped. Verified it's coolant, because the expansion tank is low. So I cleaned up the puddles, and left the car over night last night with a piece of card board underneath to see how long it takes for the leak to appear. Today after maybe 16 hours that area is still dry.
Some back story - my indy replaced the oil cooler and installed an aluminum Bufkin pipe back in 2019, about 30K miles ago (134K miles today). So I tend to rule out the oil cooler. Have had no other coolant issues since, until this one. I am wondering about cooling hoses around the back of the engine, which I think could be original, or maybe to/from the transmission cooler. I need to get under there and take a look, but asking if anyone has any experience with this kind of leak. Thanks...
Some back story - my indy replaced the oil cooler and installed an aluminum Bufkin pipe back in 2019, about 30K miles ago (134K miles today). So I tend to rule out the oil cooler. Have had no other coolant issues since, until this one. I am wondering about cooling hoses around the back of the engine, which I think could be original, or maybe to/from the transmission cooler. I need to get under there and take a look, but asking if anyone has any experience with this kind of leak. Thanks...