Coolant overflow tank overflowing?
 

I am having a problem with my coolant overflow tank over flowing and loosing coolant.

For a long time I had my overflow tank mounted on the strut tower, with the bottom of the tank near the same level as the bottom of the radiator, without any problems. Then, about a week and a half ago, it started filling up (I always kept it empty, never had any issues with it). I moved it back to the stock location thinking maybe the level it was at was causing it to overflow, but the problem persisted.

It started off kind of slow, it didnt really overflow very quickly, but now I need to add coolant (into the radiator, the overflow tank is full, but I empty it most of the time) after every time I drive it. I am getting tired of washing coolant out of my engine bay, what would be causing this?

The crazy old man I work with said it was my thermostat, but he is crazy (I honestly think he is :eek: ) and I dont understand how the thermostat could cause the overflow tank to overflow.

oh, its an '82 GS... if that even matters

First try the radiator cap. When it doubt change it out.

Also make sure that the overflow hose is not leaking, either from loose connections or from cracking/holes.

Finally, make sure that the rubber hose going from the overflow cap to the bottom of the overflow tank (I assume original tank?) is not swollen and fallen off or bottoming out on the bottom of the tank

Nutshell primer: When the coolant heats up, it expands, and the radiator cap first allows it to build pressure to n psi, regulating this by bleeding coolant out to the overflow tank. When the coolant cools back down, it creates a vacuum, and the radiator cap allows this vacuum to draw coolant back into the system. If the radiator cap is faulty, it can allow air to leak in, and air is easier to draw than coolant, so coolant keeps going into the overflow without getting sucked back into the system. Likewise if the hose leaks.

The tube in the overflow tank is tricky. If it fell off, then it sucks air in instead of water. If it's bottoming out, it won't allow coolant to flow back in, but it will let presurized coolant go into the tank, like a one way check valve.

thanks, peejay! It must be the radiator cap, the hose in the tank is still intact, although it might be leaky. Ill replace the hoses and the cap, just to be sure.

Ziptie the hose in the tank tightly to the cap and make sure it doesn't bottom out. Fought that for a week before I figured it out. :)

A busted waterseal would cause the overflow tank to overflow.

Yeah, but Im not leaking or burning any coolant, Its just spewing all over my engine bay. Besides, my engine only has ~20k miles on it, I really dont think I would have lost a seal already. Its never been overheated.

Yeah, but Im not leaking or burning any coolant, Its just spewing all over my engine bay. Besides, my engine only has ~20k miles on it, I really dont think I would have lost a seal already. Its never been overheated.

Place your coolant tank at or slightly below the top of the radiator. Its possible that the lower coolant resivior is filling normally then starts to siphon coolant out because its lower. If you've cleaned a fish tank you should know what I'm talking about, your bucket has to be below the tank to drain the water.

A good radiator cap SHOULD stop the siphon if it happens, but you could be getting a pretty strong vacuum it may overcome the spring.

Check your coolant level at the radiator too. That goes for everyone all the time. Your return from the overflow can may not be working correctly. Don't trust it.

I did :D

it has to be the thermostat, there's no other alternatives Lotus :nono:

Note to self: Read more carefully.

that would be my take. When my old engine was having problems, the additional pressure from the leaking waterseal would make the overflow tank, well, overflow. Check to see if you have built pressure on the cooling system like first thing in the morning before you turn the engine over. I think another indicator is the engine running and being able to see bubbles in the radiator with the cap removed. If you have these symptoms I'm afraid you have a waterseal problem.

Busted waterseal would cause coolant loss, white smoke, and difficult startup with lots of stumbling.

Might be the thermostat, grasshopper. Be sure to get an OEM part and mount with the jiggle stick up.

B

Well the car starts pretty good, considering my carb is way out of adjustment. (I dont know how to adjust it, but I will be buying a new car very soon)

I get no smoke after the inital poof upon startup. Ill check for built up pressure overnight tomorrow morning, but I have removed the radiator cap when the car was cold many times in the past week or so (to add coolant) and there has never been any pressure built up.

Also, when Im at work tomorrow Ill let it warm up with out the radiator cap so I can check for bubbles. The coolant should flow smoothly from the left to right, correct? (looking twards the front of the car)

Can someone please explain how a bad thermostat would cause my overflow tank to overflow? :confused: (or did I miss the sacracsam?)

thanks for all your help, everyone!

If it is stuck open it'll be letting coolant flow when it shouldn't be. If its closed then the coolant will be building pressure instead of flowing. Pressure causes the rad cap to vent and fill the overflow.

Ok, I understand. Thanks!

Hey, I I found the problem. I checked out my radiator cap and the seal for the lower part is torn up.

Rad cap: it happens. Especially to those carded caps at Kragens.

B