97 GTS spews coolant ONLY if heater is set to defroster

[Cratica]

I've had an issue with this GTS since I've owned it (5 years) and I want to try to fix it finally. The heater works fine, ac works great, etc... However, if I move the dial to defrost so that it blows air up the dash vents to the windshield, it dumps radiator coolant out the right side of the car near the side sill (that's where it comes out so somewhere near the heater core I suspect). Very odd I agree. It does not do this when selecting the heater or AC, only on defrost.

Anyone have a clue what might be causing this and where to start looking? Or is it an obvious heater core issue in which case it needs to be replaced? Or is there something else, some other valve perhaps that's leaking the coolant only when the valve is on from turning the heater control to defrost mode?

Thanks for any tips!

[SNKEBIT]

Check the valve on top of the heater box. Right behind the air intake box for the heater system. Right side.

[dave6666]

I would suspect it is always leaking, whatever it is, but when the internal air gates to the HVAC box are positioned for defrost it allows the coolant to escape by the visible path you have noted. In heat mode the coolant must be going elsewhere, or just pooling / accumulating waiting for you to defrost again.

At least that is my best guess from behind a keyboard.

The heater core circuit is not selective as to if, or if not, the HVAC is using the heat in the core. It always has coolant pressure to it, but when not flowing, will not be hot. That is the purpose of the valve, to remove coolant heat input, but not coolant pressure.

My point is, I would suspect whatever is leaking always leaks. It's just a matter of when you see it.

I would assume you've inspected the surge tank area? If it had a problem the leak could run down thee top of the wheel well on to the sill. I would be pretty obvious tho so you may have already ruled that out.

I would also suspect you should be able to smell the coolant in the car, but you make no mention of that which is odd.

[Bugman Jeff]

Captain Obvious here, you're sure it's coolant and not just water dripping off the AC evaporator?

[Cratica]

Thanks guys. Yes, 100% positive its coolant and LOTS of it. No, no smell of coolant inside the car when heater is on. When I turn the dial to defrost, I get a nice coating of coolant on my windshield along with the sweet sour smell of coolant and a nice dump of it out the right side behind the right front tire. Runs down somewhere near the front of the right side sill onto the ground. Surge tank? Not sure what that is but if its the same as the overflow tank in front of the right front wheel then yea, that is fine. No leaks there.

[SNKEBIT]

If it puts a film on the windshield, heater core is bad.

[daveg]

Put a pressure tester on it and start searching.

[Cratica]

Anyone have a good how to on extracting the heater core? lol

Also, can a heater core be repaired? Too hard to find a new one of these for a reasonable price. thx!!

[dave6666]

The surge tank is the one under the hood on the right side wheel well. The overflow tank is in front of the right front wheel hidden behind the front fascia.

[Cratica]

Thanks Dave, both those tanks are fine.

[Dan Cragin]

Check the advice SNKBIT gave you. Run the car with the heater on, fully warmed up, check for leaks at the heater core inlet and outlet on the passenger side underhood heater core connections. There was an issue with the clamps at those connections back in the day. 310-597-6295 if you need help.