OK! I just bought this car over the weekend, its an 89 GTU. I knew it had a coolant leak because it was leaking pretty good in the ladies driveway, but then after i left her house it wouldn't leak any more. This scared me a little but i wasn't having any overheating and the over flow tank is full....she actually filled it to much, and the sub-zero tank has coolant.

So i've got a sparatic leak that apparently isn't attached to my overflow tank and tonight my add coolant light started freaking out and driving me crazy. I checked the hose with 2 90 degree bends that goes into the throttle body and a couple of other spots but i can't find anything.....anyone have any ideas?

Why would my add coolant light and that god awful buzzer being going off randomly with seemingly all my reserviors full? This is driving me crazy and i have searched but can't really find anything. Please help a poor pathetic noob out!!!!

Also the leak looked like it was coming from the back side of the motor.

 

Have you checked the filler neck? I've had my buzzer go off twice, and both times my reservoir was full and had to add to the filler neck.

If you have checked it, and it's good, then you may have air bubbles in the system. There's a writeup somewhere on this Forum about properly removing the bubbles. Of course, if you are in fact leaking coolant, you may have bigger problems that I cannot assist you with.

 

i checked the filler neck this morning and it was infact the cause of the buzzer going off. But anyone have an idea of why the reservior would be full and the radiator empty? I'm going to autozone or advanced tomorrow to get a the tool to pressurize the system to see if i can pinpoint the leak. Also gonna look for that right-up. Thanks jpk

 

A Lisle coolant funnel (or a cut two-liter bottle of soda...depending on budget) will make filling and bleeding the coolant system much easier. Not sure about S5's, but S4's have a bleeder screw at the top of the radiator that needs to be opened in order to fill the system properly.
Regarding the full overflor/empty rad question, this could be caused by bad seal on your rad caps, the hose between the rad and overflow bottle, the overflow cap, or anywhere else in the cooling system for that matter. The fluid won't get sucked back into the engine as the coolant cools down and contracts. The pressure tester will help you find this type of problem if you have it, except if it is the rad cap. Had a similar problem and it ended up being a tiny leak under a rad hose that didn't lose coolant, but let air into the system as it cooled down.
Could also be caused by bad coolant seals, but start with the coolant system pressure test first.

 

Check the small diameter hose that connects to the overflow tank. That hose transfers coolant from the overflow tank to/from the engine/radiator depending on the temperature of the coolant. When the engine heats up and the coolant expands, the excess flows into the overflow tank. When the engine cools off and the coolant contracts inside the engine/radiator, some coolant is sucked back into the engine/radiator. If that hose has even a very small leak, it will not hold a vacuum and so the coolant will not get sucked back into the filler neck as it's supposed to.

 

The over flow tank has nothing to do with the coolant that is in the engine. The over flow tank catches the any extra fluid caused by pressure.

If the radiator is low, you need to fill the radiator, but you can't expect that the overflow tank will refill a radiator when it is low and the engine is running. The pressure cap to the overflow tank only works when there is enough fluid to cause enough pressure to open the tank.

Low fluid in the radiator = not enough pressure to open the cap to the OVER FLOW tank.

The overflow tank is not a reservoir.

 

You may want to check your cap if your overflow reservoir is full all the time
I had a similar issue once and once I replaced my cap with a new one it stopped
But I would open both caps and fill the radiator and then fill the filler neck with the car off and cold, that will ensure you being completely full.