Coolant overflow

[ike84]

Originally Posted by porschefan76

Hi Ike! I agree with not being able to determine HG failure through intermix reliably. My '09 Impreza has a HG leak on bank 1 with no symptoms other than a minor oil leak. That said, without combustion gases present in the coolant, it seems unlikely that your current coolant issue is related to a head gasket.

Anyway, having just changed out that coolant tank myself a few months back, there's only 3 real possible ways for coolant to get to that overflow tube. 1) Coolant cap 2) relief/burp valve or 3) (VERY unlikely) a crack in the top of the black plastic.

I think the burp valve will fix it for you! Pullin' for ya over here!

Fan, dude! You've seen inside the belly of the beast! Can you please explain to me how the overflow valve communicates with the main tank/coolant system? I hate not understanding stuff, and I can't find any diagrams or descriptions of what that tube actually does.

[porschefan76]

Originally Posted by ike84

Fan, dude! You've seen inside the belly of the beast! Can you please explain to me how the overflow valve communicates with the main tank/coolant system? I hate not understanding stuff, and I can't find any diagrams or descriptions of what that tube actually does.

Hey Ike! Yea, I have the Katalog as well and it doesn't go much into it. So far as I have gathered, it can (mis)function like a relief valve. I pulled the old one off of my original tank because it was working fine. It truly just bolts to the top of the reservoir with a small passage that allows it to act like "the highest point of the cooling system" similar to an old radiator cap so you can burp the system properly. However, the gaskets have been known to fail and there were a couple of threads (I cannot find them right now) that showed the valve allowing coolant out onto the top of the tank and that coolant would make it's exit out of the overflow tube. Here's a pic of my old one:

that black plug in the center is rubber and the spring force holds it closed until you use the metal tab on top to open it to evacuate air. Best I can tell from what I've heard, the rubber on the center plug gets tired or, as mentioned earlier, the rubber gasket can fail. The rubber gasket isn't shown in the pic because I disposed of it, expecting to order a new one if I ever needed to swap this valve in.

Let me know if you need more pics. I disposed of the old tank or I'd have taken a picture of the port where the expansion valve connects to the tank as well. Good luck!

[ike84]

Originally Posted by porschefan76

Hey Ike! Yea, I have the Katalog as well and it doesn't go much into it. So far as I have gathered, it can (mis)function like a relief valve. I pulled the old one off of my original tank because it was working fine. It truly just bolts to the top of the reservoir with a small passage that allows it to act like "the highest point of the cooling system" similar to an old radiator cap so you can burp the system properly. However, the gaskets have been known to fail and there were a couple of threads (I cannot find them right now) that showed the valve allowing coolant out onto the top of the tank and that coolant would make it's exit out of the overflow tube. Here's a pic of my old one:

that black plug in the center is rubber and the spring force holds it closed until you use the metal tab on top to open it to evacuate air. Best I can tell from what I've heard, the rubber on the center plug gets tired or, as mentioned earlier, the rubber gasket can fail. The rubber gasket isn't shown in the pic because I disposed of it, expecting to order a new one if I ever needed to swap this valve in.

Let me know if you need more pics. I disposed of the old tank or I'd have taken a picture of the port where the expansion valve connects to the tank as well. Good luck!

Sorry fan, I think I misworded my question (although I appreciate the knowledge on the burp valve too! My new one is coming in the mail so the more I understand about it up front the easier that job will be). You mention the gaskets - are you referring to the two o rings that sit between the valve housing and the tank?

My main intrigue is actually the overflow tube (not valve) which is the open ended tube that comes off the tank (if I remember correctly it's the lowest hose coming off the manifold) and opens to atmosphere. If the system is pressurized then how does this tube not just constantly do gas and coolant? You may have alluded to it acting as a drain for the top of the resivoir tank... Does that mean that it's only purpose is to dump coolant that comes out the burp valve or around the tank cap?

Thanks again for the time (and effort! Love the pics) in helping me!

Sent from my POCOPHONE F1 using Tapatalk

[porschefan76]

Originally Posted by ike84

Sorry fan, I think I misworded my question (although I appreciate the knowledge on the burp valve too! My new one is coming in the mail so the more I understand about it up front the easier that job will be). You mention the gaskets - are you referring to the two o rings that sit between the valve housing and the tank?

My main intrigue is actually the overflow tube (not valve) which is the open ended tube that comes off the tank (if I remember correctly it's the lowest hose coming off the manifold) and opens to atmosphere. If the system is pressurized then how does this tube not just constantly do gas and coolant? You may have alluded to it acting as a drain for the top of the resivoir tank... Does that mean that it's only purpose is to dump coolant that comes out the burp valve or around the tank cap?

Thanks again for the time (and effort! Love the pics) in helping me!

Sent from my POCOPHONE F1 using Tapatalk

Hey Ike! My bad, sorry yes I misunderstood what you were looking for. When I said gasket, I did mean the o-ring as well. Memory isn't always 100% haha

For the coolant overflow hose, you hit it on the head. It's one job is to allow coolant that gets on top of the reservoir to flow to the outside of the vehicle. Here's another pic I took:


Sorry, it's basic, I didn't want to open Photoshop. But, for orientation, brown arrow is oil fill, orange arrow is coolant fill and florescent yellow is the hole that eventually ends with the coolant overflow tube. It is not under any pressure other than atmospheric unless the cap or valve leak, then it's whatever pressure the rubber seal between the rear trunk lid and reservoir lip can maintain... not much above ambient I'm guessing. If you're familiar with the way the reservoir is connected to the rest of the system, then it is the bottom short hose that goes through the firewall and then it simply routes 90 degrees down near the passenger rear wheel well once it's through the firewall.

No problem on the pictures. Worth a thousand words and all that. Let me know if I left something out. Best of luck!

[ike84]

fan...mind=blown. i have looked on top of that tank dozens of times and never noticed that before. now i realize why though - i have to cock my head sideways up under the trunk strut to see it.

im kinda blown away right now with this info. this whole time I thought that tube acted as an overflow drain for the closed system. now i realize that all the fluid i have seen literally pouring out of that tube has either come up through the burp valve, under neath the cap, or out of cracks on top of the tank! I'm amazed that much fluid went through that hose and never once overflowed into the trunk compartment. This makes me much more confident in the decision to replace the burp valve since I really dont think there are any cracks (pressure tester will arrive soon so will know for sure at that time) and its definitely not the fill cap.

Thanks again fan! I owe you!

[porschefan76]

Originally Posted by ike84

fan...mind=blown. i have looked on top of that tank dozens of times and never noticed that before. now i realize why though - i have to cock my head sideways up under the trunk strut to see it.

im kinda blown away right now with this info. this whole time I thought that tube acted as an overflow drain for the closed system. now i realize that all the fluid i have seen literally pouring out of that tube has either come up through the burp valve, under neath the cap, or out of cracks on top of the tank! I'm amazed that much fluid went through that hose and never once overflowed into the trunk compartment. This makes me much more confident in the decision to replace the burp valve since I really dont think there are any cracks (pressure tester will arrive soon so will know for sure at that time) and its definitely not the fill cap.

Thanks again fan! I owe you!

Hey Ike! Happy to help! That port is very difficult to see from the rear trunk access. Removing the old reservoir made it much easier to identify!

I'm hoping that replacing that expansion valve will fix your issue. Like you said, there's only 3 ways for coolant to get to that hose and with a new cap and a presumably functional coolant reservoir, there isn't much else it can be!

You owe me nothing, you and a few others got me through my fuel injector/MAF issue a few months ago, I'm just happy to be able to pitch in! Keep us informed on your progress! Good luck!