I spent 4 hours under the hood of my car today, despite being probably the last person anyone expects to find elbow deep in machine entrails.
Last Saturday driving around my engine started to overheat. I pulled into a gas station, bought a bottle of coolant, walked around for a bit to let it cool off, and tried to open the radiator cap. I couldn't get it off, and I'd only ever been under the hood of one other car, so I thought maybe the tube leading to the radiator cap was where I put the fluid. So I filled up the overflow tank (olol) and managed to get it home, redlining the heat gauge for a solid mile.
Skip to last Sunday - I figured out how to get the radiator cap off, and the radiator was wet, but not filled with fluid. I took it to Firestone, just a few blocks away, since it needed an oil change anyway. I asked them to do a pressure test on the radiator while they had it, and they found a leak near where the aluminum was welded. They wanted some ridiculous amount of money for it - I think the initial estimate was 500+ (for all the hoses/fittings, and shit like tag bulbs, etc). I couldn't really afford it, and they brought the price down to 450ish, but I knew the radiator itself was only about 100. The tech was really nice, and he showed me what I'd need to do to replace it myself, and even recommended an online retailer. I'd already watched a really good youtube video on replacing a radiator, so he was able to point out things on my vehicle that I knew about.
The radiator showed up here on Friday ($100 online with shipping), and Saturday I figured I'd drive it around before I did any serious work and see if the problem was just a product of the insane heat last weekend. Firestone had topped off the radiator, and when I checked, there was visible fluid. I found myself wondering if the problem might be the thermostat instead. It drove fine for a few minutes, got up to optimal heat, and stayed there for about 3 minutes. Then it overheated, and by the time I got it home there was so much heat that I didn't want to work on it.
Today I pulled out the old radiator (after much swearing, three trips to Auto Zone for tools I didn't have, and a gnarly hand wound across the knuckles) and put the new one in. I'm certain I reconnected everything properly. I filled the radiator with fluid, closed the lid, and took it for a test drive. I was fine for about 5 minutes, then I saw that slight uptick from optimum temp that signaled it was going to get hot, so I turned around and headed home. It got to redline on the way, so I pulled over and popped the hood. The coolant in the overflow tank was boiling, and there was a drip from the upper hose where it connects to the thermostat housing. But that hose was clamped tight, the crimp-style clamp was exactly where it was before I took it off, I could tell because of the indentation. In fact, now that I think of it, I didn't even remove the upper hose at that connection point. I did loosen the clamp and try, but it didn't budge, so I just moved the clamp back.
When Firestone tested it, they said it wasn't a head gasket. It's not the radiator or the radiator cap, and it's not the radiator fans. So that just leaves the thermostat, right? Is there any part of the cooling system that I'm not considering?