So three years ago I was driving over Loveland Pass in Colorado, and right as I approached the summit, the engine temp flew up to the red and all my coolant poured onto the ground. I had to get it towed to a shop, and they informed me the cause was the radiator cap failing because the seal had gone bad. They replaced the cap, and all has been well for three years.

Until yesterday. I was on my way home from climbing a mountain and then suddenly, (after a pretty aggressive maneuver I will say), I saw my engine temperature go up close to the red. I gave the throttle a rest and turned on the heat, and fortunately I was going down a big hill so I left it in 4th gear and let engine braking do its thing and the temperature cooled back down to normal. I turned off the heat just because I was cooking, and everything was fine continuing down the hill. Then, I started ascending the next hill on the highway, and the engine temperature gauge started rising again. I turned the heat back on and it was only blowing cold air. The temp kept rising to red so I pulled off the road and shut it off, and subsequently steam came pouring out of the radiator cap. My car also gave me a low oil light and check engine light.

Opened up the hood, witnessed steam continuing to pour out the radiator cap, checked the oil and saw that it was low. There was still oil on the dipstick, but it was down below that bottom level marker. I guess this makes sense to me as my car has burned oil in the past and led to a low oil level. I haven't checked the oil level in a month so it probably burned down to that low level over time. I don't know if the level was low enough to cause increased heat in the engine... if there was still oil showing up on the dipstick and it was of good color, do you think it was low enough to cause additional heat stress?

Regardless, there was no coolant in the tank after it finally stopped steaming and I had to get my car towed AGAIN. There was also visible green coolant sprayed on the engine.

So what I'm assuming is that the radiator cap failed AGAIN. The heat not blowing hot air right at the end, in conjunction with the temperature gauge blowing up, I assume was due to a loss of coolant through the radiator cap seal. Then I guess the coolant boiled and steamed out as the engine got hotter when I pulled over. When I first noticed the engine temperature rising yesterday, my guess is that was the official break in the seal of the radiator cap, but there must have still been coolant in it, and then with going down the long hill with engine braking and having the heat on, maybe that kept the cooling system working even with the faulty cap. But then once I hit the gas again on the next hill, only minutes later, that faulty seal led to overheating once again, coolant blowing out of the cap, the heat not working and the steam. The check engine light I imagine is related to the cooling system, and I wonder if perhaps the oil light came on right before I turned off the car because the sensor was triggered by those other issues?

The only other thing that confuses me a bit is that it seemed like right before I turned the car off, while I was pulling over, that the engine was dying. The RPMs started dropping really low like down to 400rpm. This was in conjunction with the oil pressure light and the steam blowing out of the radiator cap. The temperature gauge at that time had just touched red, it never went higher than touching the red before I turned it off. Could it be that the engine was too hot and somehow that was causing it to die right there at the end? Like I said, I turned it off so I didn't really get to evaluate what was going on in that regard.

Is this all related to the radiator cap failing once again? I know I need to add oil, and it has no oil leaks but like I said, that's been going on for a while. Let me know what you think. If it's a different cooling system issue, or a different issue entirely, could that cause the radiator cap to leak? Or do you think the CAUSE is the radiator cap leak? Thank you all. My truck has been towed to a local shop and they told me they can't even look at it until next week so I'm trying to figure this out on my own.

BTW: 1999, manual transmission, 3.4, 240,000k.