Overheating question: gauge temp normal, coolant boiling/overflowing

Hey guys, haven't posted in a while. My baby finally has a problem and I am curious to see if anyone else had the same thing. I hit 100k in January. Never had a problem.


Drove to the airport to pick up my parents, idled "under" the airport for about 5-10 minutes with A/c on while waiting. After I picked up my parents, I noticed that the a/c was blowing warm air. Didn't notice/don't remember if it was warm while i idled. I turned off the a/c, got on the highway, drove to my grandmas (about 25-30 miles) and when I parked i noticed that the gauge read higher than usual. In 7.5 years of driving i have never seen the gauge move from it's "normal" spot. 15 minutes later I added just a little bit of water to the overflow tank and radiator. Started driving and 4 miles later the gauge went through the roof, I turned off the car. I waited for a while for the car to cool. Then added more water and drove home (another 5 or so miles) without a problem, and gauge red normally all the way.

My commute is 10 miles with 4 of those being on the highway. Every time I drive, the temp gauge reads normally. It doesn't move. But when I come to work, I check under the hood, and the overflow tank is full to the top with coolant. My radiator does have a small leak right where the spout is (where you pour the water into it) attaches to the radiator itself. The coolan't "sips" out, but it does not leak out. Also, when i turn on the car and watch the overflow tank, I see bubbles rise up inside.

Maybe the thermostat is bad? but the temp would be higher. 15-20 minutes of driving, some of it on the highway, is more than enough for the engine to reach normal operating temp so that thermostat opens. If the thermostat didn't open, then the coolant in the overflow tank would not be hot either, since it never makes it inside the engine, right? Could it be the cap not keeping pressure or because of the small crack? I tried replacing the cap with one from advance auto parts and after doing the same commute, i checked under the hood and i thought the overflow tank would explode. the coolant was literally boiling inside of it. so much so that the overlow tank that i replaced 2 weeks ago got slightly deformed.

anyways, sorry for the long story. any ideas? suggestions? should i try a cap from the dealership? should i replace the radiator? where do you recommend getting a radiator? i don't plan on getting rid of the car anytime soon.

if you havent flushed your coolant yet I'd say to go ahead and do so and replace your thermostat while you're at it.

and if thats not it, maybe your head gasket?

i runned with the same problem before,it maybe to things first ill say thermostat if not,check if your radiator fan is working? if not you have to replace the fuse (relay) it might be blown.....pmed me if u have any questions ill more than happy to halp out

Think EMmsp might be barking up the right tree.

Sounds like a similar problem I had on a domestic about three years back. Would be fine around town but when you got out on the highway - the headgasket was leaking enough to put excess pressure in the coolant system and force coolant into the overflow and out the oveflow. Not leaking enough to smoke while the motor was sitting at normal idle.

Might have someone do a pressure check on the system to see if you can detect some internal leakdown.

Could be worse - brother called me about a female friend of his that had a head gasket replaced on her car. She said it would not start the next morning. It was really low on coolant but nothing wet on the ground. I pulled plug number one - green liquid. Number two - green liquid. Each cylinder was full of coolant. Good thing is was a four cylinder or she would not have had enough fluid to fill all the cylinders...

Thermostat. It's becoming a pretty common failure point on these things

EDIT Re-read your post. The crack in the radiator may be the proverbial smoking gun, not letting the cooling system get up to pressure.

Your talk of bubbling in the coolant reservoir just gave me a flashback to my GM car blowing its head gasket 6 months ago. It started off where the temp gauge would rise a little above normal after getting off the highway. And there was bubbling in the coolant (exhaust gasses leaking into the cooling system). Pretty soon I couldn't drive the car more than a minute without there being so much exhaust pressure in the cooling system that it would dump all the coolant onto the ground. A way you could check if the bubbling is in fact exhaust gas and not just the coolant boiling over is this nifty device they sell at napa called (if i remember correctly) something like a leak-down test or something. Its basically a bottle filled with a blue liquid that you put on your coolant overflow tank or instead of the RAD cap and when the bubbles pass through the liquid it will turn yellow if it detects hydrocarbons (exhaust gas).

Oh and I could be completely wrong too, I don't claim to be an expert on these things, I just figured I'd share my head-gasket experience with everyone.

thanks everyone for checking in and posting suggestion.

i did the radiator flush at home twice. obviously didn't get all the old fluid out, but got some of it. the coolant in the overflow though is this rusted orange color, even though i have refilled the radiator with distilled water only.

the fan is working. what i noticed lately is that after a drive when i park, it continues to run where as before it would turn off after 2-3 minutes, no it just keeps running.

the reason i don't believe it's the thermostat is that the coolan gets hot. so the hot coolant must be exiting the engine into the radiator/flow tank. and if the "cooler" coolant wasn't going back into the engine, the temp gauge would read higher than usual and it does not. asumming of course it's working correctly. but it does go down when i turn off the car so i think it is.

advance auto parts actually made things worse. i don't think it was able to hold pressure as well as the stock cap.

the a/c works fine now and does blow cold air. the heater works as well

so after taking everything into account, i think either the radiator is not keeping the pressure because of the crack and it goes into the overflow or the head gasket is bad like some of you mentioned.

thanks for all the suggestions. keep them coming if you have more. and how much does a pressure check cost at a shop?

Just went through this

I had the same basic thing going on - coolant sensor was getting hot, boiling coolant out of the overflow. In my case turning the heat on full with the fan on high seemed to help as a stopgap. Took it in to the shop, apparently it was the thermostat but got a flush and fill at the same time.

I might've tried to repair it myself, but

• I don't have a good place to work on it
• My wife would have killed me

I was just reading through the discussion of replacing the timing belt and water pump yourself, and I suspect that in 10-20k miles I'll pay someone to do that as well, but I'll take a printout of that whole thread for them to read through first.

Sounds like a blown headgasket, or a warped head now that it over heated

But like you said, it might just be the hole in the radiator

No just change radiator cap letting go to soon (Head Gasket how stupid)

The hole in the radiator is allowing the system to suck air in. Air can't cool your engine, only coolant can. You've definitely got to fix THAT first, and then see where you stand. The cooling system must be sealed to work properly. New radiator shouldn't be too expensive, and replacing it should be a Saturday afternoon job.

The radiator takes like 15 mins max to change.. Literally

4 bolts and, 3 hoses, and a sensor.

And I said maybe head gasket because I miss read the post. I thought he said there was pressure in the radiator when he opened it up (don't know why I thought he said that) and it overfilled the overflow tank.

But now that I re read it, it sounds like its just that crack that stopping it from keeping pressure

yea i missed the crack in the radiator thing too, I thought he said that his radiator cap was leaking and he replaced it and there was still a problem. If there is in fact a leak besides the replaced radiator cap than that would make sense. He did specifically say that he tried two different radiator caps though.

thanks everybody for reading the extra long post and answering. the last few posts give me reassurance that it's just the radiator and not the headgasket. yes, i can do the radiator myself and i haven't worked on the car in a while so i am actually looking forward to it but not to the part of spending $200 on a new one. that's how much they are at advance auto parts.

i guess the economy stimulus payment that i got on friday is going to that.