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I have a 2006 PT Cruiser.
Back in December 2017, there were 2 occasions where the engine started smoking. But it was very obvious that coolant had barfed out of the overflow tank(the temperature was not high though).

Fast forward to July, the car starts trying to overheat. It would go above the 50% mark and sometimes the 75% mark, but it never got into the red zone. Turning the heater on full blast would help temporarily. (Like 5min and then the temp would rise again)

I took it to a mechanic after that happened. The mechanic could find no leaks, and every time he drove the car(highway, city, country, everywhere) he drove it everyday for a week. it didn’t over heat a single time . But we replaced the thermostat, and he also said he was 99% sure it was a pressure issue (forgive this description. I know nothing about cars) but he said that the pressure was weird, and it was causing coolant to go from the engine into the overflow tank, thus making it barf out coolant from the overflow tank, and overheating due to the coolant leaving he engine. So In addition to the thermostat, he fixed that.

Okay. Got my car back. I’ve been driving it daily for a couple weeks. It was doing totally fine; even on long drives (40+ Min during hottest part of the day). And then yesterday when I was a drive thru .... it starts overheating again.

I checked the coolant level - it was low. So I start filling it up. I poured in over 50% of the entire coolant container and the level did not rise AT ALL. I saw no leaks. There are no wet spots, or smoking, or puddles. I checked the passenger side floor - heating core does not appear to be leaking. I see no wet spots or stains nor do I smell anything.

Mechanic is closed on weekends so I can’t take it until Monday.

Any ideas?
 

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You don't need to be pouring the coolant into the plastic overflow container, you need to be pouring it into the radiator filler neck. You have to remove the radiator cap to do so. If it's low, it might take you a few minutes and it may bubble up on you. Be persistent. Ideally, the level should be right at the bottom of the cap when you remove it. You need to see if the cooling fans are working. Unfortunately for you , 06 is the first year of the TIPM (totally integrated power module) so a defective relay can't be checked. Start the car, open the hood and have someone turn on the a/c. You should be able to hear a fan come on and feel air blowing over the engine from between the radiator and the engine block. If you don't feel any air moving, odds are you need to replace the cooling fan. If it's working, I'd suggest you go to your closest auto parts store and purchase a new radiator cap. They don't cost that much and MIGHT be the source of your problem. The car is 12-13 years old and if that's the original cap, it won't hurt to replace it anyway. And don't buy the cheapest one they have. Get a good quality one. Ask the parts counter person which one they'd put on their car. That's about all I can suggest since you say you're not a car person or a mechanic. I'm not a mechanic, either, but have been working on my own cars for over 45 years. First things first, though, remove the radiator cap (when it's cold, not hot) and add the proper amount of coolant to get it to full.
 

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I agree with chuzz. Also, the overflow has a hose that pushes fluid to the overflow container, then when the engine cools, has to suck fluid back into the engine. Quite often, with the age of the car, this hose will crack a tiny bit and you can push the hot fluid into the overflow container, then when it cools the tube is able to suck air instead of fluid, which is difficult to spot this problem most of the time. There should also be a clamp on each end (radiator nipple and the overflow canister). So from your symptoms, besides a bad radiator cap, the fluid pushes out, then when she cools she sucks air, then your fluid in the engine and radiator is low, then the air expands greater and pushes more fluid out, then she starts overheating. This symptom is common on old cars that did not have overflow containers and might be happening with you. Also, just to be safe, check the oil to make sure there isn't white or creamy substance with the oil, just to know the head gasket isn't leaking for now.
 

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Discussion Starter #4
You don't need to be pouring the coolant into the plastic overflow container, you need to be pouring it into the radiator filler neck. You have to remove the radiator cap to do so. If it's low, it might take you a few minutes and it may bubble up on you. Be persistent. Ideally, the level should be right at the bottom of the cap when you remove it. You need to see if the cooling fans are working. Unfortunately for you , 06 is the first year of the TIPM (totally integrated power module) so a defective relay can't be checked. Start the car, open the hood and have someone turn on the a/c. You should be able to hear a fan come on and feel air blowing over the engine from between the radiator and the engine block. If you don't feel any air moving, odds are you need to replace the cooling fan. If it's working, I'd suggest you go to your closest auto parts store and purchase a new radiator cap. They don't cost that much and MIGHT be the source of your problem. The car is 12-13 years old and if that's the original cap, it won't hurt to replace it anyway. And don't buy the cheapest one they have. Get a good quality one. Ask the parts counter person which one they'd put on their car. That's about all I can suggest since you say you're not a car person or a mechanic. I'm not a mechanic, either, but have been working on my own cars for over 45 years. First things first, though, remove the radiator cap (when it's cold, not hot) and add the proper amount of coolant to get it to full.
I am adding it to the radiator - not the over flow.
If I top it off - the coolant will be gone again in 1-3 days. And when I filled it the other day, I used practically the whole container of coolant and the level never rose
 

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OK, the fluid has to be going somewhere. So here is a test. With the engine cold, fill the radiator up, if possible, park on a slope so the radiator is a little higher than the rest of the engine. At this point, use water (or bottled water, doesn't matter at this point, save the antifreeze mixture until this is done), squeeze the radiator hose a little bit to make sure most bubbles are out. Turn the heater knob to the hottest setting. Start the engine and with the radiator cap off, watch what is happening. You may see a few bubbles to start with, but they should stop. As the engine heats up, the level should rise when warm, although it may actually drop during the first couple minutes, so keep topping it off, this is purging the air out of the head, hoses and block. By the time the radiator fan comes on, she should be warm and fluid should be gently overflowing very slowly. Don't worry about this right now, and when this does start to happen, check your temp gauge, see if it is straight up and down. If you see lots of bubbles when the temp is at the halfway point, you have issues, and if the fluid level drops all the sudden with a big bubble, another big problem, so hopefully that does not happen. If none of this happens, great. Put the radiator cap back on, watch the temp gauge a couple minutes and make sure it stays at the halfway point, do a couple gentle revving of the engine, say five or six times about 20 seconds in between), then shut her down. Fill the overflow to the full mark at this point so you can check the level after she cools down half an hour, it should drop a little bit after she is colder. If not, overflow tube has an air leak and that is the problem, she is sucking air instead of fluid, and since it is so slow and such a small amount at a time, you would have difficulty detecting it.
This test should take about half an hour to 45 minutes, check around the thermostat housing on the head for any leaks (it's right below the filler cap), along with any wetness on the overflow tube ( by wiggling it a bit up and down, side to side, if she shows wet she is worn out).
Let us know what happens and we can go from there to diagnose.
 
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All great suggestions by Dana44. Do what he said and post back.
 

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Hey, Annikaemvy, Chrononaut here. My 1987 Reliant, 2.2 is doing the same thing. Her coolant would be low by morning (more and more required every day), overflow bottle always full and puking over, overheating, excessive system pressure and no leaks. I replaced the thermostat twice as well as the radiator, water pump, lower heater hose that was leaking, radiator cap and the coolant temp sensor in the side of the water box. The final verdict? Blown head gasket. Yep, blowing coolant scented steam out the tailpipe last night, coughing while starting (small amounts of coolant in the cylinders after shut down), motorboating at idle (sips of coolant in the cylinders), requiring nearly a quart of coolant before start up now. She runs pretty good when warmed up, though. Clean oil and oil cap. Just two weeks ago I had the the thermostat and the sensor replaced. The mechanic swore he'd fixed the overheating issues that had started just before I had her smogged at the beginning of July. Nope. Two days later back to square one. Returned her to the shop where the tech said he couldn't do anything more for my car and "I should take it to a guy who knows these cars". So now it's back to the shop for an expensive repair. I hope your car doesn't need a head gasket like mine, but at least I know where my car's coolant was going!
 

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Oh, yeah, forgot to mention. ever since the mechanic replaced the coolant temp sensor, the engine cooling fan comes on whenever the ignition comes on. His response to this? "Wow, I don't know, but the fan always being on's not gonna hurt it!"
 

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I had a simlar issue with my old 01 PT not returning coolant to the radiator from the expansion tank. Turned out I had a lose overflow hose connection at the radiator neck. Coolant would not leak out when flowing to the expansion tank but the small leak broke the vacuum and coolant would not return to the radiator when cooling down. A hose clamp on the over flow hose connection solved this.
 
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Oh, yeah, forgot to mention. ever since the mechanic replaced the coolant temp sensor, the engine cooling fan comes on whenever the ignition comes on. His response to this? "Wow, I don't know, but the fan always being on's not gonna hurt it!"
I suppose it's not really going to hurt but it shouldn't be too hard to find and fix the issue which could be as simple as a bad or improperly grounded temp sensor.

Unless your car uses input from that temp sensor to adjust the fuel mixture then it's going to run way too rich.
 
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Back to the original poster - some leaks may not be obvious by visible inspection on a hot engine. The car (and also the radiator cap) need to be hooked up to a cooling system pressure tester to see if the system holds pressure. This will find leaks you can't always see otherwise.
 
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