So I'm pretty new to this forum and have read some of the posts in the searched content for overheating problems and a few of em caught my eye but I'm not still too sure what it could be maybe if I can explain it might help.

The other day got a full oil change car has been running great for a while. It's a 1999 Eclipse GS, Anyways woke up this morning to warm up my car since its freezing where I live the temperature was like 9 Degrees this morning. So start the car starts up fine, and i go inside to let it warm up for about 5 or so minutes. I go out and get ready to leave and notice my temperature gauge is at the top so i immediately turn the car off and pop the hood. Little steam was coming out of the radiator cap and opened it up and saw it was just about boiling over so let it set and cool off for a bit and then started it back up and the needle started to go back up again towards the top so i shut it off. I'm figuring it could have something to do with the frigid temperatures and the thermostat. Or that it didn't have enough antifreeze. So bought some antifreeze and put it in there and started the engine up. little smoke coming from under the heat shield of the manifold then the plastic over next to the engine on the passenger side starts making this annoying hum sound when i put pressure on the plastic cover the noise goes away. as soon as i let my hand off it starts making the noise again. then white steam or smoke started coming out of that so i shut the engine off and decided to come here for help. Sorry for such a long story but thought you guys could help. If you have any suggestions on what it could be please inform me. Thanks!

First off, welcome to 2gnt! Post some pics of your car in the introductions section

That plastic piece houses your timing components.

If white steam is coming from there, you may have a leaking HG on that side.

You may have a bad head gasket either way.

Do a compression test and post up your results.

Also, you may want to remove those plastic pieces and inspect for where exactly its coming from. Check the little bit of connector hose between thermostat houses and hard lines, they leak all the time. In fact, I always carry the materials to fix that piece.

The guy I bought my 97 RS from blew a head gasket next to the plastic cover and it damn near melted it in one place. It warped it a little and made the same noise for a couple weeks. I guess it finally "rubbed itself in" but it's gone now. I'll inspect it when I do the timing belt in the coming months. And yes, carry a piece of connector hose. Mine leaked right after I replaced the thermostat. I'm new to these cars so I'm limited but you can trust the fellas here. Finally...welcome!

Lets see; thermostat, fan, radiator cap, low coolant level, too much water in the coolant (i.e. ice in coolant channels), water pump could all do that. I think I would start with those before I jumped to the headgasket.

You've had no indication of problems until just this point, right? No leaks, no overheats, no funny idles etc.?

But that isn't to say its not the problem, just that I would start with the simple stuff first. If it was ice in the coolant passenges, then you could also have a bad water pump as a result. If it was low coolant, then you could also have a bad water pump as a result etc. If it overheated for too long, then you could have a bad HG and water pump as a result. Did the cooling fans come on during this? If not, then start there.

Honestly, if it was me, I would start off with replacing the thermostat and the radiator cap (provided the fan is coming on) because these are relatively cheap and easy things to do and there is no harm in doing them. But if you want to you can take out the thermostat and put it in water and bring to a boil to see if it works (opens fully). You can then bring your cap somewhere and have it pressure tested to see if it works.

A couple of avenues to start.

Captain Caveman

96 RS Turbo 11.414 @ 119.62 MSNS, Crower 2 NA cams, BW366, 10.5 comp, UDP, 60mm TB, W/A intercooler, 3.55 tranny 567.9whp 430tq
97 RS NA 13.188 @ 103.87 MSnS powered 12.5 comp, Crower 3's and 219.4whp with 175tq
98 RS DD 12.5 comp on stock ECU, LTH, Crower 2's, Koni, GC, Hypercoil, DG hats
99 OZ 5sp Stocker 15.856 @ 85.97
99 GS stocker auto 17.7@77mph!

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Yes, Haven't really had any problems until this. I am going to change out the Thermostat and try a new cap and probably some hosing that goes from the housing to the Radiator and see how that goes before i jump into anything else. Thanks for all the info. though guys I really appreciate it!!!

1999 Eclipse GS

So I took the car to a friend of mines shop today and am letting it sit over night in a warm temperature regulated room. I don't think it's the head gasket because if it was the tailpipe would be blowing white smoke and the oil would be somewhat of a milky color unless the oil went into the antifreeze. After driving it to the shop for the first time today once the car warmed up the temperature went up quick then when i pulled into a parking lot and and kept it in drive without accelerating the temperature went back down. I think that the Heating core (correct me if I'm wrong) is blocked possibly and/or the water pump is bad. Plus I'm putting the new thermo. and upper radiator hose in tomorrow morning. Also I was talking to a friend of mine and he said that If it was filled with water originally and no antifreeze the car wouldn't have driven, cause it would have at least blown a freeze plug and most likely cracked the block from the temperatures we had. Plus after letting the car warm up in the heated room there was no water or antifreeze leaks of any kind under the engine area.

Does this sound correct to you guys?
Thanks for all the input again!

1999 Eclipse GS

It could very well be a water pump. The heater core is a possibility too. Either way it will be a pain. Have you tried a compression test yet?