I have a 2001 Oldsmobile Bravada with about 160,000 miles. At first I could hear a faint gurgling sound from the right front side under the hood when I’d stop and go. Then about a month later my truck started running hot (at 230°F or so), so I checked the coolant even though I had just put some in two weeks prior, and there was hardly any. I refilled and it was going like crazy. And on top of that, the heater in my truck goes cold when the gauge starts to go over 200°. When it starts to get close to the red, the heat suddenly goes hot and my gauge goes back down to around 150°. Also, when I’m on the highway it switches from hot to cold a lot less than in town, or does it slower.
There is a leak: it kind of looked like oil, but I use Dex-Cool antifreeze, so it’s red.