Jks2327

I have a coolant leak - i'm losing coolant fast but can't find any puddles, leaking, or streaked dry coolant ANYWHERE! Only other symptom is that my heat doesn't work even when car is at temp.

Oil is not milky and no white smoke, so hoping head gasket is ok.

No coolant under the gas pedal, or fog on the windows.

Car isn't actually overheating because luckily I caught the low fluid level and have just been driving to try to diagnose. Running fine otherwise. No engine codes (related ones anyway).

Maintains pressure when at temp. Also, replaced reservoir/cap about 9 months ago and no issues till now.

Any help or ideas would be appreciated!!

2004 Audi A4 1.8T quattro

Highmile

Really odd. See what happens whem you bypass the heater core. I make a little U shaped pipe with pvc elbows from the hardware store. Pull the hoses off the heater core, insert the U shaped bypass pipe, and continue testing. Any catalytic converter or turbo codes?

Highmile

Double post. Sorry!

steveracer

Not sure what "fast" is, but perhaps I can help. I have a 2002 owned since new and have had similar issues.

1. Have you checked the coolant flange on the back of the head? Common problem, search for repair on this site.

2. I have had a radiator that seeped coolant and finally replaced it last year. At same time I replaced heater core, but did NOT have to do so as it was not blocked. Apparently the coolant leaked down enough to cause air bubble in core, so that had heat only when revved high. Look between radiator and AC core for leaks. I could also see small wisps of steam out of front grille as a telltale.

Arondale7

I'm not sure about 1.8T motors, but I do know they have aux. water pumps (it's a small $90 part about the size of 2 sticks of butter). When it leaks, you may not see the fluid. On a 2.7T, the aux water pump is in a funny position requiring the removal of the intake manifold to replace. Also, on a 2.7T it will leak onto the engine and eventually on or around the downpipes which would boil off. You may want to check it out. I would not drive it regularly at all until you have it checked out. Make sure to check the fluid in the AM and before you drive home from work if not driving another car. Coolant leaks can escalate quickly and the result can be a cooked motor. Also make sure you are still using the red G12 coolant and not green antifreeze and especially not water.

Hope this helps.

A4 GH05T

+1

Pothole5000

Clean your engine bay really well.

Drive a few days, then gat a 6 pack, flashlight and a mirror. There will be dried coolant residue somewhere. You can also get uv die and add it to your coolant, and with a uv light it will glow wherever it is leaking.

Start first with the coolant flange and that sensor on the back of the block. Typically it leaks there, runs down the back of the engine / bell housing and evaporates before hitting the ground.

ECS Tuning-Audi

Most common place for a leak is the rear coolant flange. Start looking around near the firewall on the passenger side of the engine bay.

Usually it will drip down the side of the transmission.

Other areas are the the front of the engine near the crank pulley. This would indicate the o-ring on your water pump has failed or is beginning to fail. If you still have a belly pan install it would be tough to spot puddles as it usually will catch drips/leaks.

Jason