As poorboy mentioned, you already had a rotted through freeze plug??? How soon and they weren't brass???

And as many already said, if you had a cold lower hose you definitely weren't getting circulation, so it isn't JUST the gauge, and you have to figure out the circulation issue. Start with the suggestion of running it with the cap loose and heat on high and see if you get circulation and burp any air out if you're lucky. But if you had a plug rot out already, something is going on inside the block.