Coolant pouring out of reservoir when trying to fill

[jmonica]

Hi Everyone. I attempt to fill my coolant reservoir (Overflow tank is what I call it), and as soon as I start filling, coolant just dumps out of it and ends up behind the passenger side tire. I have read some posts about a heater control valve behind the coolant reservoir being a likely culprit and I was wondering if anyone had any useful information?

The vehicle operates at normal temp and the radiator remains full and I don 't have any leaks except for when I try to fill the OF tank. Has anyone run into this problem before? I am going to remove the tank, but I was hoping to only have to do it all once and order the part ahead of time, if its likely to be the heater control valve.

Does it ever feel like your vehicle has reached the point where every single system or part that can fail is doing just that? I spend all weekend every week just fixing one problem after the other with this jalopy. Today its the upstream O2 sensor, top and bottom control arm bushings, ball joints, wheel hubs and backing plates. Then when I can afford the parts, the rack and pinion needs to be replaced so I will be pulling it all apart again for that. Last weekend, the evap system, before that the brake control module / system, after replacing the front calipers / discs /pads, after removing the fuel tank and replacing the fuel pump, after replacing the spare tire cable lowering system and exhaust heat shield, after fixing the rear hatch handle mechanism so I could open the hatch to get to the hole that lowers the spare tire, after replacing the sunroof, blower fan and resistor, the steering column switch, wiper washer and headlight washer motors, the horns and as part of the yearly maintenance, the sway bar control arms, then replacing the rusted out transmission cooler lines, exhaust gaskets, steering wheel position sensor, and I know I am forgetting a litany of smaller things I've worked on. The sad part is that my list of things still left to do is about as long as what I've already done to it since January this year. sigh... Thanks for letting me vent.

 

[Mooseman]

It could be the tank itself. It can crack and cause leaks on its own. That's the only reason that would cause the symptom you are describing. EXT/XL trucks do have a vacuum operated rear coolant valve but it's in the heater coolant lines and would not leak simply from filling the OF reservoir. The tank on this platform is truly an overflow tank that is out of the coolant circulation as opposed to the full size trucks where their tank is inline with the heater hoses and pressurized. Ours aren't.

I hear you on the never ending repairs but it's expected on any older vehicle in the rust belt. My 07 TB, despite being well cared for and pampered by the PO and myself, is also showing its age. Have to replace the power steering lines due to rust and starting to get body rust. Even my 11 Caprice is starting to show it's age even though it's not driven in winter. Just recently had to replace the starter and I'm getting a front wheel shake.

Same as us, parts fail. It's part of life.

 

[jmonica]

It could be the tank itself. It can crack and cause leaks on its own. That's the only reason that would cause the symptom you are describing. EXT/XL trucks do have a vacuum operated rear coolant valve but it's in the heater coolant lines and would not leak simply from filling the OF reservoir. The tank on this platform is truly an overflow tank that is out of the coolant circulation as opposed to the full size trucks where their tank is inline with the heater hoses and pressurized. Ours aren't.

I hear you on the never ending repairs but it's expected on any older vehicle in the rust belt. My 07 TB, despite being well cared for and pampered by the PO and myself, is also showing its age. Have to replace the power steering lines due to rust and starting to get body rust. Even my 11 Caprice is starting to show it's age even though it's not driven in winter. Just recently had to replace the starter and I'm getting a front wheel shake.

Same as us, parts fail. It's part of life.

Thanks Moose. I'm going to pull the tank and check it if I ever get done getting this O2 sensor out. Been trying for two days.

I hear ya. This car has been through a lot in the last 17 years. Winters are brutal and it's got a lot of miles on it. I just hope my old body doesn't stop working before the Envoy. Actually I guess it wouldn't matter at that point.

I will post pics if and when I discover the source of the leak. Thank You again for the info!!!

 

[Blckshdw]

You don't have an actual leak per se.... It's a design characteristic of the overflow tank. With the cap off, if you look carefully towards the firewall, you'll see where it's open in the back to allow excess coolant to spill out. I didn't grab my pinhole camera, but you can kinda see it in this pic.

That dark area, is open to the engine bay, and where your coolant is spilling from when you've added too much.