Coolant overflow

[ike84]

I am losing my damn mind here

A month ago, on first drive after extensive modifications (none to the cooling system) I was running hot and spewing coolant out the overflow tube.

I drained the system, replaced the TStat with a new BW low temp TStat, refilled, burped, all the good stuff. While the system was empty and the hoses unclamped, I stuck my scope up in the water pump (original pump) - impeller blades looked fine. Took the drive belt off - no play in the bearing. I also put a new cap on for ****************s and giggles (.04 version, replacing a .04 version, just because). Also, convinced that I had cracked a head during the mods, I tested the expansion tank for exhaust gasses - none present.

After that, no more overheating! Back to running on the 1 of 180.

But I am still spewing coolant out of the overflow tube! Looking at the caps in the trunk, when the system is hot, everything looks fine and there are no leaks. There is also no coolant in the trunk anywhere.

What the hell is going on here? It's like the system is over pressurizing. I'm at a total loss here. I've ordered a pressure tester to see if I can find any leaks in the system, but I don't think that's the issue. I've also ordered a new burp valve and a new cap, purely because I don't know what else to do.

Is there a valve in the overflow tube that could have gone bad and now the thing leaks anytime the system is pressurized? Does anyone know exactly how that works? I've scoured the e-katalog and fsm and there's really no explanation of it in either of those documents.

Any insight here would be greatly appreciated. I don't have any hair left to pull out.

Best,
Ike


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