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Discussion Starter #1
While chasing a slow cooling system leak I've the the need to drain and refill my radiator three times (that another story). Each time following established guidelines. when my thermostat opens after getting hot enough and while watching the coolant with the radiator cap OFF I always get overflow out of the radiator all over the shop floor. It's more like an eruption. How can I avoid this overflow? I'm going to install a new radiator and would like to avoid the mess again. On most cars the flow starts and bubbling is witnessed below the neck of the radiator. But this car belches up and out. Any help would be appreciated. My car is the 96 Geo Tracker 1.6. New hoses, clamps, and thermostat that is recently new and running fine for the passed 6 months.
 

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I've moved your post to this section

Do you not have a coolant overflow / recovery tank? :huh:

That should contain the excess coolant from normal expansion, assuming that your rad cap is operable as designed.

IF you don't have one, it is customary to run a rad level an inch or two low (measured cold) to allow for expansion of coolant.

You also have the option of adding an aftermarket overflow tank, if you have the room to mount one.

Have you sampled the radiator for presence of exhaust gases? You could have a head gasket leak if all else is in check. :(
 

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Discussion Starter #3
Maybe I wasn't clear Max. I do have a recovery tank but I'm not talking about normal expansion etc. I'm taking about the refill and burping process. Without the radiator cap on doing the initial refill and burping process my coolant erupts out of the radiator neck when the thermostat opens. After the eruption I'm able to finish the refill process and all is well. It's the initial burp mess I'm trying to avoid.
 

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Then your coolant tank should capture that initial "eruption" (air purge) with the rad cap on, IMO. :)

If you didn't have the rad cap off, then you probably wouldn't even notice this occurrence, and after several heat / cool engine cycles you would only need to bring the coolant tank level up to its normal point.
 

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Discussion Starter #5
Thanks Max
Are you than saying, that I should have the radiator cap ON after the refill of coolant, and that the recovery tank will handle the burping air and resulting overflow of coolant? My manual tells me to leave the cap OFF until after burping. Am I missing something?
 

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You can burp all over the floor / ground with the rad cap off, OR allow the recovery tank to do its thing with the aforementioned driving / cool-down cycles and the subsequent re-topping off the recovery tank.

That's how I do it anyways.

The other option is to not fill the rad so far (just to you can SEE a level) and then allow the expansion to take place within the confines of the rad. That would limit the mess, but you still need to monitor the recovery tank level and add to it appropriately. ;)
 

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Discussion Starter #7
OK,
Thanks Max I'll give that a try when the rad install is completed. Thanks for your input.
 

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Hmmmm.....I would not expect the coolant to explode all over the place when you are burping the system with the cap off. Normally, when I would replace my coolant, I would try to park on a bit of an incline where the front of the car is higher, fill the radiator to under the rim and the overflow to the cold level, start the car with the cap off, and watch for air bubbles the gurgling in the radiator, letting the engine run. The level should actually go down when the thermostat opens, and I would need to top up.

Edit: I would have the heater on high, as well.....
 

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Discussion Starter #9
That's what I thought also Bex. But as I'm watch the coolant down in the neck of the radiator, it's like when the thermostat fully opens the level of the coolant starts to rise rapidly and doesn't stop until it overflows. I turn off the car, the coolant settles down, I refill to the bottom of the neck, restart and all is fine.
 

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After draining mine, I just fill it slowly, listening for the air to be done escaping before adding more. Doesn't take that long really. Then I fill the overflow a bit over the line to allow for it to finish burping, put the caps on, and drive and it burps naturally. It has always ended up being mostly full from how I fill it, very little needed to be added after it burps the air out.
 

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But as I'm watch the coolant down in the neck of the radiator, it's like when the thermostat fully opens the level of the coolant starts to rise rapidly and doesn't stop until it overflows. I turn off the car, the coolant settles down, I refill to the bottom of the neck, restart and all is fine.
Hmmmm. I wonder if it's your radiator being partially plugged up, without a proper path for the coolant to run through the radiator when the stat opens, thus backing up and out the fill? :huh:
 

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Discussion Starter #12
Good thought Max. But if the radiator was partially plugged I would not expect to get normal operating temperature once the radiator is full and flowing normally. I run with the temp gauge in the car at about half reading. Has been that way since I got the car about a year ago. But, maybe even with a partially plugged radiator I'm still getting good enough flow to control operating temperature.
 

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Normally, when the thermostat opens, the coolant level will drop (as the coolant is now allowed to pass) rather than rise......?????
Of course, air in the system will cause this rise in coolant as well......
 

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Normally, when the thermostat opens, the coolant level will drop (as the coolant is now allowed to pass) rather than rise......?????
Oh I agree under "normal" circumstances.

My thought is that when the thermostat opens in his case (and with a partially plugged radiator) that the previously block held coolant has nowhere to GO, thus an apparent rise in rad level. It's just a theory? :rolleyes: Maybe not a good one.
 

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Discussion Starter #15
Max,
Again you were right. After I found my slow leak in the radiator I ordered a replacement. I just got it installed and after close examination of my old one I found that most of the core tubes were really corroded and semi plugged. After the new rad was installed, refilled, and engine started....no more explosion out of the cap connection when the thermostat opened.
Thanks to you all again....this forum is awesome.
 

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Nice!

Glad that it's sorted and up and running! :)
 

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That is why, in the OLD days, we took the caps off and rodded the core..

Oo! did I date myself?...

.... Philip

Note: if you use distilled water in coolant the puss wont accumulate so fast...
 

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Also remember never to let the level of the overflow tank drop to a level where the tube in it can suck air into the radiator.
 
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