Potential Coolant Leak

Hi all. So kind of a premature post as I haven't even got under the car to investigate, but noticed a small leak under my car at work today , I was parked on gravel so wasn't even sure it was for sure. Got home and slid a piece of cardboard under. Just checked it, seems to be a small amount of fluid leaking which I think may be coolant. It's dripping pretty close to where the oil drain plug would be ( assuming its running down from somewhere and dripping onto the ground). Anyway I know this is extremely limited info until I get under the car, but if it is coolant leaking from that ballpark location any insight as to where it might be coming from or potential issues?? Thanks in advance!

As well I hope you are all getting through this crazy time.......

First thought was EGR cooler.

STDOUBT said:

First thought was EGR cooler.

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Cheers thanks !! Appreciate that. I will check it out

Could also be the coolant temp sensor O-ring or the the o-ring under the coolant glow plug housing to the head both over time tend to harden shrink and or crack......I’ve had it happen to both on my cars.

csstevej said:

Could also be the coolant temp sensor O-ring or the the o-ring under the coolant glow plug housing to the head both over time tend to harden shrink and or crack......I’ve had it happen to both on my cars.

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thanks for this . First thing I checked was my install of my coolant Heater , but think that is all good. I did my CTS years ago I will check it. Thanks!

My coolant leak was from about that same area, turned out to be the coolant flange located under the vacuum pump had some seepage that was migrating down the back of the engine and dripping behind the oil drain plug.
It took fluorescent dye and a UV flashlight to find it in my case.


If that turns out to be the source, you'll have to replace the o-ring on the flange after draining the coolant.


Most important.....don't just snug down the flange bolts to what you think is about right, most flange leaks occur from over tightening the bolts.


Torque it to 7ft. lbs. with a good torque wrench.

U4ick said:

My coolant leak was from about that same area, turned out to be the coolant flange located under the vacuum pump had some seepage that was migrating down the back of the engine and dripping behind the oil drain plug.
It took fluorescent dye and a UV flashlight to find it in my case.


If that turns out to be the source, you'll have to replace the o-ring on the flange after draining the coolant.


Most important.....don't just snug down the flange bolts to what you think is about right, most flange leaks occur from over tightening the bolts.


Torque it to 7ft. lbs. with a good torque wrench.

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Awesome thanks for the info! What was the damage on the parts? Also where did you put the dye?? Gonna check this all-out!

My ordeal cost me.....$4.99+ free shipping for UV flashlight on Ebay
$7 or 8 bucks for dye from Advance Auto parts

$1.99 o-ring from I.D. parts


Pour the dye in the expansion tank and run it awhile.

My coolant is green colored now like I'm running the wrong antifreeze.
Shining the light under the engine after dark, even the tiniest speck of coolant will show up as bright yellow.

U4ick said:

My ordeal cost me.....$4.99+ free shipping for UV flashlight on Ebay
$7 or 8 bucks for dye from Advance Auto parts

$1.99 o-ring from I.D. parts


Pour the dye in the expansion tank and run it awhile.

My coolant is green colored now like I'm running the wrong antifreeze.
Shining the light under the engine after dark, even the tiniest speck of coolant will show up as bright yellow.

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Great thanks for this!!

Hey all so an update on this. This problem totally corrected itself not long after posting in the spring. I was unable to find the leak and it completely stopped leaking. All summer didn’t leak a drop. The last few days however ....... got the leak again. So I literally just winterized my car and all was fine and dandy. So the only things I can see that changed are :

1- I plugged in my inline coolant heater while winterizing to test it. Ran it for half hour or so seemed to work fine. Could this have somehow caused something to leak a few days down the road ??

2-The overnight temps are cooler these last few days getting down to just above freezing. Could the cool weather be causing it ?

Any input is greatly appreciated !! Maybe someone had had this exact issue before and can shed light on it. I will also refer to the posts from the spring on the issue , it stopped leaking before I had a chance before. Thanks in advance !

O-rings and seals are pretty resistant to temp swings, IF they are in good shape. If a seal is old and on it's way out, it's way more susceptible to pressure deltas and temps. Sounds like you have a seal failing somewhere.

The culprit could be anywhere, but because of it being by the drain plug, I would check the following:

• Coolant flange on the head, driver side
• Plastic coolant flange, facing towards you (houses t-stat)
• EGR Cooler as mentioned above
• Hard line (below) the t-stat housing that goes into the block
• Waterpump seal

Anything that is leaking on the engine could run down and collect near the oil plug. The way the engine is tilted towards the back of the car causes leaks (like oil and coolant) to catch on the lip of the block where the oil pan bolts to and run around the backside of the oil pan, then run down the lip onto the pan.

There are other places and connections to check, but those to me would be the starters. I don't think anything near the coolant bottle nor the other coolant hoses are close enough to that area to run to where you are describing.

^^ ok thanks ! My plan is to take it for a short drive tonight then pull it in the garage on ramps and start trying to track down the leak. On a side note now that I think of it when I checked the coolant heater I was under the car and it seemed like maybe there was a hair of coolant dried on the top of tank heater None had ever dropped from that area but maybe this is an indication that the leak is up by the head amd a very small drop rolled down the outlet hose of my heater and onto the top of tank.
Thanks for the reply. Man I got on it early and was looking tip top shape for winter and now I gotta figure this out !!

WolfgangVW said:

^^ ok thanks ! My plan is to take it for a short drive tonight then pull it in the garage on ramps and start trying to track down the leak. On a side note now that I think of it when I checked the coolant heater I was under the car and it seemed like maybe there was a hair of coolant dried on the top of tank heater None had ever dropped from that area but maybe this is an indication that the leak is up by the head amd a very small drop rolled down the outlet hose of my heater and onto the top of tank.
Thanks for the reply. Man I got on it early and was looking tip top shape for winter and now I gotta figure this out !!

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Yeah good luck!
I've fixed every possible coolant/oil leak I can think of in my car at this point. I've owned it since 2013 (Dec, so very end) and just this last month I finally solve...knock on wood, my final leak. It was very small but it was the rear main seal. Would never have known unless I had to swap my clutch out.

I've done all of the above I mentioned above, including the oil cooler. Coolant is a PITA because you have to drain and fill the system EVERY time. I've done it about 5x now through everthing I've done. I know a lot of people will say "don't fix it till it's broke" but at the age of these cars, if all of the above things (and some others) haven't been done, it's worth doing them while the coolant is out.

The one that was the biggest PITA was removing the hard line to get to the seal on the end of it. It just required removing a bunch of stuff to be able to pull it towards the rear of the engine (driver side). Pretty sure I posted a thread on the forums of how to get to it/where it's at for others reference.

KrashDH said:

Yeah good luck!
I've fixed every possible coolant/oil leak I can think of in my car at this point. I've owned it since 2013 (Dec, so very end) and just this last month I finally solve...knock on wood, my final leak. It was very small but it was the rear main seal. Would never have known unless I had to swap my clutch out.

I've done all of the above I mentioned above, including the oil cooler. Coolant is a PITA because you have to drain and fill the system EVERY time. I've done it about 5x now through everthing I've done. I know a lot of people will say "don't fix it till it's broke" but at the age of these cars, if all of the above things (and some others) haven't been done, it's worth doing them while the coolant is out.

The one that was the biggest PITA was removing the hard line to get to the seal on the end of it. It just required removing a bunch of stuff to be able to pull it towards the rear of the engine (driver side). Pretty sure I posted a thread on the forums of how to get to it/where it's at for others reference.

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ok awesome thanks ! I kind of get what you mean on coolant on smaller scale. Years ago I had a code coolant temp reading low. Well I decided to replace the CTS to see if that solves it. Of course I might as well cut corners right ? And not drain the coolant amd just quickly swap before too much came out. Well you can guess how that went. After making a mess and draining the coolant anyway I finally get it replaced. Then a few months later I’m draining again for the thermostat replacement. So yes I totally get the logic behind draining it properly the replacing the parts or seals at the same time.

WolfgangVW said:

ok awesome thanks ! I kind of get what you mean on coolant on smaller scale. Years ago I had a code coolant temp reading low. Well I decided to replace the CTS to see if that solves it. Of course I might as well cut corners right ? And not drain the coolant amd just quickly swap before too much came out. Well you can guess how that went. After making a mess and draining the coolant anyway I finally get it replaced. Then a few months later I’m draining again for the thermostat replacement. So yes I totally get the logic behind draining it properly the replacing the parts or seals at the same time.

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Haha... Yeah the CTS... I've learned my lesson with shortcuts; I've found a few that work... And handfuls that didn't.

KrashDH said:

Haha... Yeah the CTS... I've learned my lesson with shortcuts; I've found a few that work... And handfuls that didn't.

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Ha cheers to that!
So mini update. Pulled the car in and messed around with it as long as I could ( well I ended up getting a bunch of crap in my eye as I was under the car which took me an hour to flush out lol ) But anyway still not sure on the source. The coolant is dripping off or around the axle/boot to the driver side of the drain plug oh maybe 8" or so when you look from underneath. From the top after removing the airbox hose I can see definite coolant presence somewhat underneath basically where the CTS is, possibly a hair to the passenger side as well. Like dripping on the flywheel housing or whatever. My first suspect was the O-ring for CTS was leaking and thought I had it nailed but I couldn't pickup any residual coolant when I wiped a white rag directly under where the CTS meets the flange like the underside of the hose. But almost directly underneath is where coolant has dripped.

So again any insight is welcome. I still need to dive in a bit but inspected for quite a while . Other than CTS in this area what's the next culprit??

Or possibly it is the CTS O-ring and any residual coolant dried before I wiped??

The CTS O-ring is a notorious leak point on these engines.

WolfgangVW said:

Or possibly it is the CTS O-ring and any residual coolant dried before I wiped??

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Is the car a 5 spd?

KrashDH said:

Is the car a 5 spd?

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Yes the car is a 5 speed manual

WolfgangVW said:

Yes the car is a 5 speed manual

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If I remember correctly...the metal coolant flange has 2x seals...one against the the head, and also there is an o-ring between the glow plug flange to the coolant flange...sounds like 1 of these could be worn out?

Yes possibly. How bad are they to change ?? At this point I might just do them both and the CTS unless it’s quite the process!

Was just trying to find a DIY for the coolant flange seals replacement for the 5 speed ALH , anyone know where to find one ?

KrashDH said:

If I remember correctly...the metal coolant flange has 2x seals...one against the the head, and also there is an o-ring between the glow plug flange to the coolant flange...sounds like 1 of these could be worn out?

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So I picked up three seals from the dealer. The coolant flange to the head, the coolant flange to the glow plug flange, and the CTS O-ring as well as some extra coolant. Whats in my car now is fairly new so I'll reuse what I can and have some on hand. My plan is to drain the system tomorrow and just replace all three seals. Any tips on changing these three seals?? Anything to watch out for?? Like can I run into seized / stripped bolts etc or are there any common snags? Thanks in advance !!!

As well any special tools recommended!?

WolfgangVW said:

As well any special tools recommended!?

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As far as that/those flanges go... Nothing special. All common tools. Drain coolant, take your time!

KrashDH said:

As far as that/those flanges go... Nothing special. All common tools. Drain coolant, take your time!

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Thanks!! Is there a DIY around or pretty much self explanatory??

So another update! I know I said I'd just change all 3 seals , which I will. Didn't get much time today as its Thanksgiving up here and was busy with family ! Managed to find time to head out to the garage and tinker a bit this evening. Pretty sure I discovered the leak is the coolant flange to head. Ran the car while up on ramps and tried to inspect with a flashlight, couldn't see any dripping. So I shut down and wiped any areas I suspected , thought I saw a slight pink residue from by coolant flange to head. So long story short I took a clean paper towel and rolled it up and stuffed under the flange by head, let run for a bit and sit for a bit. Pulled it and yes a hair of pink coolant. Think that's my slow leak.

So what's the torque spec on there flange bolts?? I've seen 7lbs and 9lbs in my research. Same for glow plug flange? As well think I should replace CTS with a new one while I'm at it? I have the O-ring to replace and seems to function fine, I replaced but was probably 7 years ago. Anyway thanks again for all the help!!

Honestly, while it's out, I would do all of the seals you can get to in that assembly...especially if they're 7 years old.
Remember the rule of thumb for DIY mechanics...if you choose NOT to, it will immediately spring a leak from what you didn't replace.

Have to remember too, although slow leak, once you stop that leak, the system will have a bit more pressure since that leak isn't causing a pressure delta...if other seals are close to on their way out, once you plug one area, there's potential for the weaker seals to fail.

Haha ya isn’t that the truth !!
good point about the pressure I’ll definitely change all seals