Coolant Leak from Rear of Engine- Only leaks once engine is warm

[LINDW4LL]

My car just sprung a pretty big coolant leak. The leak only starts after the car has been running for ~15 minutes or so, and then it starts pissing it out from somewhere at the rear of the engine towards the middle of the car at a pretty good rate. To give you a rough idea of the leak's speed, I'd guess the coolant tank would be empty within 15 minutes after it starts to leak.

It literally does not leak a single drop when the car is just sitting with the engine off, nor does it leak at all until after the car is warmed up.

I have looked at the rear of the engine but cannot spot the leak from above, nor can I see it from underneath as the bellhousing is in the way. I plan to go in and delete the aux water pump, but I'm not sure if that could leak at this rate or if the leak not starting until the car is warmed up makes sense in that scenario.

Any ideas? Thanks!

[FlyboyS4]

That pump and the RMS seem to be two common points of failure causing coolant leaks.

[Monty23]

Heater core hoses, RMS, turbo coolant lines. Pull the downpipes and take a look around.

[ElementR]

I've had both the aux pump under the intake and a coolant line feeding my driver side Tial result in similar leaks. Best thing to do is pick-up a system pressure tester (or if you trust your air compressor regulator, use it) and slow increase pressure to 5 psi or so and you will likely see the leak assuming you can get your head back there (this is done with engine off). A small mirror on an extendable swivel arm comes in handy... Harbor Freight has them.

[MetalMan]

I believe the 2.7T uses the same or similar hoses/connectors as the 1.8T, for the heater core hoses? The heater core hose as Monty mentioned has an O-ring in the connector itself that deforms over time. This is the connector that mates it to the coolant flange.

[christianb5s4]

If it's the heat core supply hose that leaks (like mine very intermittently does), here's a DIY explaining the issue:

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

[Tjtalan]

I would guess coolant pipe on the back of the heads. Thermostat opens and it starts pissing.

[pman928]

I have the same exact issue, I think it is the aux pump line to the turbo, but I am interested to see what others find out

[LINDW4LL]

Thanks for the tips everyone! Just checking back in with the solution.

It was indeed the auxiliary water pump. The plastic that is the front output/nipple had degraded and must have finally given up a few weeks ago causing the sudden (and fast) leak. I replaced the pump with a 1x1" brass elbow and it's now leak free.

[DrBoost]

I think I have a problem with the rear coolant crossover pipe and looking for pics or diagram to understand if it is something easily fixable. I think the coolant crossover pipe at the back of the passenger side head is leaking really bad. I found a piece of gasket sitcking out if someone could LMK if that is what it is?

If so is this an easy (or since it is a B5, should I say humanly possible) repair without taking the engine out?

Thanks

[n8henn]

This is the clip (or at least part of it) that holds in the Coolant Temp Sensor.

[Monty23]

looking for pics or diagram

http://www.myaudis4.com/2016/10/17/c...g-replacement/

[DrBoost]

Perfect thanks, that is what I was looking for and it looks like it is going to be a serious PIA to replace with the engine in the car.

[Silverex]

Not really, space is limited like everything on these cars tho.. Might help to take Intake, Y pipe off, and spider hose to gain alil more working space. . I’d replace the both sensors/clips/o rings since they are both cheap and you’ll probably break them on removal. Some silicone spray and twisting and pulling and the sensor will eventually come out

[Monty23]

It's definitely not a good idea to pull the engine for a coolant sensor. Or even coolant cross over pipe o rings. They are all plenty accessible from the top.

[DrBoost]

This is the clip (or at least part of it) that holds in the Coolant Temp Sensor.

OK I see now, its the coolant temp sensor that is leaking should be an easy fix. The pictures helped. All the parts stores have the sensor but none of them have the damn clip!

[DrBoost]

It's definitely not a good idea to pull the engine for a coolant sensor. Or even coolant cross over pipe o rings. They are all plenty accessible from the top.

Thanks, although I keep looking for an excuse to pull the motor for rods and K24's lol!

Right now is not a good time to tear it apart although it looks like I may be home till April 6th with nothing better to do. I have another car tore apart right now and would like to get this one back in service.