Another mystery coolant leak

First off, the car just rolled 230K.

The first hot day of the year (a couple weeks ago), the coolant light comes on and sure enough, I'm low. I filled it with pentosin and distilled water. Two days later, the light came back on so I inspected it for leaks and didn't see anything. A buddy came over with a pressure tester and still no coolant leak found.

Late last year, I did the TB and replaced the water pump. Pulled the inspection cover and it doesn't seem wet near the water pump. At the same time I replaced the coolant flange and thermostat, which that doesn't seem to be leaking either. The heater core was replaced a year and a half ago. The car does not smell like coolant when running and does not overheat.

It's gotten to the point that every other day I'm adding fluid so the light doesn't come on. This is REALLY annoying.

The coolant expansion tank had a little residue on it and makes a hissing sound when cooling off (I think it's just the coolant moving around).

I plan on starting with replacing the tank and cap unless y'all have other input.

Thanks!

I've found that if you have exhausted every option, look towards the head gasket. Look for white smoke.

Also, this time of year I'd just put water in it until you can figure it out.

belome said:

Also, this time of year I'd just put water in it until you can figure it out.

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I am now.

ChrisMc said:

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I plan on starting with replacing the tank and cap unless y'all have other input.

Thanks!

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I wouldn't replace anything until I found some signs of leakage. Check the radiator surfaces, inside under the heater core and underneath the car.

Check the expansion tank seal. There should be no hissing. Daughters Audi had the same issue. Replaced the tank cap and seal. End of issue. Dr

Every other day is a lot. I have a similar issue that I go 400 miles before the light comes on. If you do a pressure test and you see that the level has dropped, pull the glow plugs and crank before trying to start. I almost locked my motor like that by not thinking. Also, EGR coolers are known to leak and the coolant would just get burned out of exhaust.

Make sure you don't have coolant migration through the level sensor. Found an aftermarket bottle on my car that started to do that.

ChrisMc said:

First off, the car just rolled 230K.
The first hot day of the year (a couple weeks ago), the coolant light comes on and sure enough, I'm low. I filled it with pentosin and distilled water. Two days later, the light came back on so I inspected it for leaks and didn't see anything. A buddy came over with a pressure tester and still no coolant leak found.
Late last year, I did the TB and replaced the water pump. Pulled the inspection cover and it doesn't seem wet near the water pump. At the same time I replaced the coolant flange and thermostat, which that doesn't seem to be leaking either. The heater core was replaced a year and a half ago. The car does not smell like coolant when running and does not overheat.
It's gotten to the point that every other day I'm adding fluid so the light doesn't come on. This is REALLY annoying.
The coolant expansion tank had a little residue on it and makes a hissing sound when cooling off (I think it's just the coolant moving around).
I plan on starting with replacing the tank and cap unless y'all have other input.
Thanks!

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Your issue sounds like over pressure in the system blowing coolant out of the cap relief valve, when i’m testing headgaskets I use this method on diesels. I think you should start with this before spending money on the tank/cap.
Link below, bear with me he’s actually very smart and has some good info to help you.
https://m.youtube.com/watch?v=8WsXUXUBb0c

I got bad news for the OP -- it's probably the head gasket. You can get a test kit at NAPA that will tell you if there are combustion products in the coolant. If you get a positive read on that then, well..... significantly bad news.

I experienced the same exact issue. It turned out to be the head gasket. I was in denial about this for a long time. I did NOT have any while smoke. Symptoms: Consuming coolant & leaking heater core due to system over pressurized from exhaust gasses entering the cooling system from bad head gasket. It was easy to dismiss because the engine ran fine until one day it over pressurized so badly that it blew the cap off the coolant bottle while driving (LOUD! like a hand grenade exploding under the hood). I do not recommend this experience. Not fun Don't be like me. Do the right thing. Stop driving it. Pull the head and get it re-worked by a reputable automotive machinist.

Took the vehicle to Apex Tuning to get a real diagnosis, they came back and said the coolant expansion tank is leaking. I tend to trust them. I will replace it and see what happens.

If that's all, then great!
Just be prepared for the possibility of the headgasket, though I'm sure many will agree in hoping it's just a bad tank!

ChrisMc said:

Took the vehicle to Apex Tuning to get a real diagnosis, they came back and said the coolant expansion tank is leaking. I tend to trust them. I will replace it and see what happens.

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That's what I thought too. I thought my coolant tank or cap were leaking. Unfortunately it was leaking due to system overpressurized due to bad head gasket. At first glance it looked the the coolant tank or cap were leaking.



Good luck and update us.

I just had the tubing nipple on my expansion tank crack. It would hiss slightly if the overflow tube was wiggled. No signs of a leak, but I was losing coolant very slowly. I always refill after a timing belt change with 60% coolant/40% distilled water, so I just kept it topped up with water.



Replaced it with a new expansion tank from IDParts - no more hissing, low coolant levels, etc..

Please provide update Chris. Inquiring minds want to know!
thx

Update: Ran fine for a couple days before I had to start adding distilled water again. Doesn't have much g13 left in it but somehow the coolant is turning a dark red/rust color. The system also holds pressure for hours. I get home from work and park it, wake up the next morning (14 hours later), crack the cap and it releases pressure. At this point, I'm going to assume it is a head gasket.

That probably is indeed the head gasket.....

https://www.kermatdi.com/i-288-arp-head-studs-for-tdi.html

The description they list is exactly what is happening to me. I plan to try this before tearing the motor all apart. Anyone have luck with this? Or any concerns?

The description is for if you're running a big turbo and the boost level is starting to lift your head off the block.


It sounds like your engine is stock, or at least Not Mega Boost Modded.


Replacing the head bolts with studs doesn't fix a head gasket leak!

Sorry, it has an egr delete and stage one tune. Does this change anything?

All things being equal, I would not just put new studs on it. Do the gasket, check for warpage, etc.

ChrisMc said:

Sorry, it has an egr delete and stage one tune. Does this change anything?

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Definitely not.


I have a stage 1 tune on my Golf with EGR tuned out, and it is very far below the tuning and hardware necessary to start worrying about lifting the head.


Please fix the headgasket by replacing it, not trying to clamp the head down with studs.


It wouldn't be the craziest thing in the world to take the valve cover off and try giving the headbolts a bit of a snug up. They are massively tight - or are supposed to be anyway. That would also let you inspect the cam and see if that needs replacing while you've got the timing belt off (2001s are notorious for soft cams).


Check here for the head tightening sequence: http://forums.tdiclub.com/showthread.php?t=230995


That last 90º is a MF'er!

Do the right thing & pull the head. Take the head to a reputable automotive machine shop. When re-installing, use the kerma ARP head bolts for piece of mind. https://www.kermatdi.com/i-288-arp-head-studs-for-tdi.html