What does this mean?? (other than I need a new radiator) (idle, engine)

[Drover]

OK, so I've been pushing my luck a bit on a 1995 Saab 900SE with a radiator leak. For about a year and a half, I've simply added more coolant as needed, about once every 2 or 3 weeks. Recently, the "coolant level low" warning popped up on the info display, and like normal, I filled up the reservoir tank. This time, the warning came on again within about 10 miles. To my surprise, the reservoir was flat empty. The next day I filled it up again and let the car idle to see what would happen. Sure enough, after about 20 minutes I'd estimate there was about half a quart of radiator fluid in a puddle on my driveway.... but then it just stopped dripping. I kept an eye on the temp gauge and it never moved past the middle. It's like some of the fluid leaks out and then it just stops leaking out, or at least after the initial gush it leaks slowly enough that there's still enough to regulate the temperature pretty well. I thought it was related to whether the coolant was hot or at ambient temp, but after the initial quantity leaked out, it never dripped no matter the temp. Why would it do that?

[Gimme3steps]

I've seen reservoir tanks have a crack about halfway up, leaking enough coolant to set the warning and make a puddle but not enough to cause overheating. Is your tank plastic?

[Drover]

It is indeed plastic. I know there's a radiator leak too and had assumed it just got a lot worse all of a sudden... I'll have to look into the reservoir and see if that's the immediate issue.

If it's the reservoir, is it possible that it would only leak when the car is running?

[Lux Hauler]

A leaking reservoir can, but typically will not cause overheating it just acts as a buffer for the coolant during heat cycles. You don't really need them if you have direct access to the radiator but it does serve as a good metric for observing leaks like in your case.

Unless you know exactly where the leak is on the radiator it is hard to diagnose the issue. To answer your question yes it is possible that the reservoir would only leak while running since it is pressurized when the engine is up to temp.

[Nativechief]

I would add a can of radiator stop leak and see if this solves it and be sure all of the hose connections are tight. . If this doesn't fix ityou will have to replace what is leaking either the tank or the radiator.

[Gimme3steps]

Originally Posted by Drover

It is indeed plastic. I know there's a radiator leak too and had assumed it just got a lot worse all of a sudden... I'll have to look into the reservoir and see if that's the immediate issue.

If it's the reservoir, is it possible that it would only leak when the car is running?

Is it a reservoir or an expansion tank?

A reservoir is really just an overflow container. An expansion tank is where you actually fill the cooling system. An exp. tank will have a pressure cap and will be under pressure when hot and will most likely leak when the car is running.

A reservoir will have just a plastic lid and won't be under pressure but if cracked,will leak down to the point of the crack.

And try to avoid using any stop leak.

[Drover]

It's an expansion tank.

Looks like I've found the immediate problem. Thanks to everyone for the info.

[SD4020]

Sounds like an easy fix. And FWIW I have never had any sort of good luck with any sort of stop leak.

[Gimme3steps]

Originally Posted by Drover

It's an expansion tank.

Looks like I've found the immediate problem. Thanks to everyone for the info.

What was leaking?

[Drover]

Originally Posted by Gimme3steps

What was leaking?

I haven't identified the exact problem yet since it takes two people to open the hood (another problem that needs addressing). What I meant to say is that I have a starting point for troubleshooting thanks to the information provided here.