Mysterious coolant leak

[jpurre]

So I have noticed a really small coolant leak but cannot for the life of me figure out where it is coming from. Sometimes it leaks, sometimes it doesn't. There is no "constant" leak. It is not the aux pump (dry all around it), it is not the infamous T (bronze replacement) and everything is dry around the tank (no pink or white colors). The coolant circulates when up to temp and t-stat opens. Radiator appears dry, lower coolant hose was replaced about 2 years ago. The only thing I noticed is the passenger side electric fan does not come on, even with ac on and at operating temp. Today the car got much hotter than usual, and I had to add coolant. When it decides to leak, the puddle forms on the drivers side, directly under the rear of the engine bay. I have a theory that it could be the coolant temp sensor for which I have a replacement already to go in. I've read that the clip can get loose and the sensor does not seat properly, hence leakage. Maybe tank cap? Anyone have any relevant input or useful info regarding this leak?

[a4kamila6]

If that clip was loose, at operating temp you would lose your coolant in a matter of 15 minutes. My friend rich changed his coolant temp sensor on his 1.8t and didnt seat the clip in properly. Im driving the thing, 15 minutes later smoke coming up from under the hood. Empty coolant tank, sensor blown out. After i put it in for him correctly all was well but damn I was shook

[Speed4Avant]

So I have noticed a really small coolant leak but cannot for the life of me figure out where it is coming from. Sometimes it leaks, sometimes it doesn't. There is no "constant" leak. It is not the aux pump (dry all around it), it is not the infamous T (bronze replacement) and everything is dry around the tank (no pink or white colors). The coolant circulates when up to temp and t-stat opens. Radiator appears dry, lower coolant hose was replaced about 2 years ago. The only thing I noticed is the passenger side electric fan does not come on, even with ac on and at operating temp. Today the car got much hotter than usual, and I had to add coolant. When it decides to leak, the puddle forms on the drivers side, directly under the rear of the engine bay. I have a theory that it could be the coolant temp sensor for which I have a replacement already to go in. I've read that the clip can get loose and the sensor does not seat properly, hence leakage. Maybe tank cap? Anyone have any relevant input or useful info regarding this leak?

Could you possibly have air in the system and it's bubbling out the overflow hose?

[S4James]

coolant temp sensor o-ring can flatten. i have had coolant randomly leak due to this.... usually overnight.

[CJ_]

I just had the hose blow out that goes from the expansion tank to the coolant rail on the back of the block. The hose blew just above the fitting on the rail so as a temporary fix, I cut about an inch off and clamped it back on. That would give you a leak right at the back of the block on the driver side.

[brandon91891]

I had just found a pestering coolant leak took me 3 months turned out to be a plastic pipe off my heater core which is under the plastic tray near your battery don't forget to check there. I had very similar symptoms with coolant in the same area I thought it was my auxiliary coolant temp sensor which I believe is the one on the drives side of the engine but it was not.

Pressure test the system is the only way. Get a bicycle pump with a psi gauge. Wrap electric tape around the air chuck until it fits snugly into the coolant hose directly in front of your reservoir put a clamp on it. in the front of your reservoir block the whole with a small screw thread it in tight or it won't hold pressure. Pump it up to 10psi the leak will show itself.


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[JB5]

Verify if any area on top of the tranny, where it meets the engine, and see if anything feels wet. if the temp sensor is leaking, you may see that the coolant can seep it's way down through the bellhousing.
if that's not the case, your rear main seal flange may be leaking.
hope this helps.

[jpurre]

Thanks for the quick responses guys. I'll do some checking in those areas.

[xalents23]

As someone else has mention check the hose that's right next to the coolant temp switch. Which is on on the hard-pipe on the back of the motor. This hose tends to rip/burst over time. Hope you find the coolant leak.

[2000s4_m]

So I have noticed a really small coolant leak but cannot for the life of me figure out where it is coming from. Sometimes it leaks, sometimes it doesn't. There is no "constant" leak. It is not the aux pump (dry all around it), it is not the infamous T (bronze replacement) and everything is dry around the tank (no pink or white colors). The coolant circulates when up to temp and t-stat opens. Radiator appears dry, lower coolant hose was replaced about 2 years ago. The only thing I noticed is the passenger side electric fan does not come on, even with ac on and at operating temp. Today the car got much hotter than usual, and I had to add coolant. When it decides to leak, the puddle forms on the drivers side, directly under the rear of the engine bay. I have a theory that it could be the coolant temp sensor for which I have a replacement already to go in. I've read that the clip can get loose and the sensor does not seat properly, hence leakage. Maybe tank cap? Anyone have any relevant input or useful info regarding this leak?

First thing to do is get that fan fixed, im guessing that water is getting hotter cause of the missing air flow and the coolant cap is releasing pressure and thats why you see it leaking from time to time and thats why its on drivers side. if water gets hotter doesnt always mean that the temp needle is going to rise, but that extra heat creates pressure and cap might not be able to handle and just opens up to release


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[JVD]

There's also a hose on the driver's side front of the motor that I had pop off. The clamp was loose and wouldn't leak until I drove for a while. Then it would randomly puke a bunch of coolant. Took me a while to track down because it would happen in traffic or something and when I would check once it cooled off at home I couldn't find it. Felt around for moisture one time and the hose slipped right off the nipple... I think going into the block.

I'll have a look when I get home so I can better describe it.

[getslideways]

Could one of your clamps for the heater hose be leaking (on the engine side). I had that issue with the passenger side connector and wrote up a DIY on it:

http://www.audizine.com/forum/showth...ficulty-Rating

The factory clamp fails to seal well with aged and swelling hoses, and can allow it to leak under different conditions instead of just constantly

So maybe the one on the driverside, second circle from the left in this photo:

[christianb5s4]

^That, I had an intermittent coolant leak for a long time that seemed to come and go as it pleased. Turned out to be the heater core supply coupler in the second from left circled fitting.

[mr16valve]

^^^^^^^
Just fixed mine yesterday.
Same symptoms.
Follow the DIY & you're golden.

[christianb5s4]

Here's the DIY for reference, you can also get your hand under the couplers and feel for any coolant.

http://www.audizine.com/forum/showth...nt+pipe+heater

[CJ_]

^That, I had an intermittent coolant leak for a long time that seemed to come and go as it pleased. Turned out to be the heater core supply coupler in the second from left circled fitting.

Yeah I had a leak there but on the other side. I tried to tighten another clamp on to slow the leak as a temporary fix, and well this happened. Luckily my buddy had a spare block with the heater core hoses cut off and the fittings still attached, so I just cut the old one off, clamped the new one on, and no more leak!

[mr16valve]

The cause of my drip drip drip.

[jpurre]

Thanks again guys. The car left me stranded on the Florida Turnpike yesterday while driving home. It got hot and I pulled over. No steam or anything. Towed to my friends shop and he is looking at it today. Ain't nobody got time fo dat. Driving a rental to work until the damn thing is sorted.

[QuinnsterKID]

Im sure your buddy knows, but if he pulls any hoses with O rings make sure he puts new ones in. Once pulled, they dont seat right again because they erode and flatten out and thats what causes small leaks. Ask me how I know Cheap insurance for sure!

[jpurre]

He has been fixing European cars for 20 years and has worked on my car before. He did my timing belt service a few years ago as well as well as my 3.5" exhaust fabbing. He will be pressure testing the system, which should show where the leak is.

[jpurre]

After pressure test, everything holds. Turns out the water pump has gone bad. I did hear something, but didn't think it was the water pump. T-stat also was not opening all the way. This was causing overheating coolant to be released through the overflow reservoir. This is the reason for the occasional puddles under drivers side. The water pump went slowly so it could not be detected immediately. So, I've got a timing belt kit ordered from ECS with 2-day shipping. This is the only logical move as the car will need to be in service position. Will be replacing coolant temp sensor and switch at the same time. Figured I'd update the thread if someone has this type of issue.

[maitai]

How did you diagnose that it was the water pump/tstat? I have similar where i am loosing coolant from the overflow but temp is fine. I had seen another thread where a blocked radiator can cause similar?