2002 Mazda protege overheated
 

Hi. I'm a girl so i don't know much if anything about cars. I'm trying to learn because it's expensive going to a mechanic. Anyways My car overheated. It chugged and the engine light came on so I pulled over and it was smoking and stunk. The mechanic is closed on Saturday too. So I call this guy who is truly a genius when it comes to fixing things and he thought it was the thermostat but it wasn't. So I put coolant in it and drove it home. It didn't over heat again but the engine light was still on. Not only this but the coolant reservoir was bubbling or air was blowing in it or something? So the guy said it was probably the radiator cap. So I went to Auto Zone and they looked at me like I was crazy for thinking it was the cap. Plus all of the coolant was missing from the reservoir all of the sudden. They told me I had to replace the coolant temp sensor to get the check engine light off. So I bought that and the cap and more coolant. Put the coolant in and cap on and the engine light turned off. Yeah!!! But I still have no idea why my car overheated. I need to know if I need to fix something else. I don't want to blow a gasket or anything like that. So my question is can a bad radiator cap cause the car to overheat? And any advise on what may have caused it if not and what should I do now? Also do I really even need to replace the coolant temp sensor?
Thanks!

There are a few things that can cause an engine to overheat, the radiator cap can be one of them. Basically, as the engine warms up, the coolant builds-up pressure and the radiator cap needs to keep the pressure in. This pressure prevents the coolant from boiling. If there's an air leak anywhere in your cooling system (like from a worn out radiator cap that isn't sealing perfectly anymore), the coolant will not build-up pressure (the pressure will be escaping) and the coolant will boil. This is what you witnessed when you pulled over and this is what happened when your coolant disappeared.

While the radiator cap is a likely culprit, it's by no means the only cause of coolant boiling and cars overheating. Keep driving, keep an eye on your temperatures, it the problem isn't solved, it will overheat again that day. Your temperature sending unit likely was still good, it's just that when coolant boils, the temperature sending unit can't get a reading and your computer starts freaking out.

Thanks
 

Thank you for explaining that to me. I feel a lot better knowing it was probably just the cap. I still need to drive it a little more to be sure of course. I'm glad I found this forum. I get so stressed out with car issues. I appreciate your reply

It wasn't the cap
 

I sure hope my car isn't toast. It made a really bad noise. I was driving it to work and watching the temperature gauge. It was good for the first five miles or so but when I increased my speed it started to heat up again. I pulled over and let it cool down for a minute and tried to drive back home. It hadn't gotten all the way up to the H yet but when I got home and turned my car off it made this clunk clunk clunk sound. The weird part is that the reservoir was way to full of fluid when it was overheating. but then it sucked it back in again after it had sit for a bit. Maybe that is normal. I'm thinking put a new thermostat in it because maybe it's sticking or something? I hope that clunk noise didn't mean I blew my engine? I'm going to try to find a you tube video about how to replace the thermostat. I really need to get back to work so I can pay for any of this. I hate this car stuff! You men are so good at this sort of thing. I'm sure there is some women on here who are good at it too. I wish I were one of them! So do you think that replacing the thermostat is the right thing to try next? Or could my radiator be bad? Or could it be multiple other things causing it? Thanks!

I don't like guessing at what part failed, there are simple tests you can do to zero-in on the issue. First and foremost, your coolant disappearing means the coolant in the radiator and engine boiled, there's only 2 ways that can happen:

1. There's a leak, preventing the coolant from pressurizing
2. The coolant just gets too hot

You can rent a radiator pressure tester, they are simple to use. Make sure your radiator is full of coolant, remove the radiator cap, attach the tool and pump the handle until the gauge reads the correct pressure. You can wait there and see if the pressure drops. If it does, try listening for a hissing sound and find it.

If the coolant just gets too hot, that is typically caused by the coolant not flowing. Most likely, the water pump isn't moving the coolant, or the thermostat isn't opening. Removing the thermostat is simple, just wait for the engine to be cold and drain the radiator. Then unbolt the black plastic flat piece air intake (it's just above your front grill) and follow the lower radiator hose (the one passenger side coming from the bottom of the radiator). You see that roundish piece of metal sticking out the front of the engine where that hose hooks up? That's where the thermostat lives. You don't really need to remove the hose, just remove the 2 bolts holding that round piece of metal and pry the piece of metal off. You may need to get a flathead screwdriver in there for leverage. Once it's off, the thermostat will be staring at you. Just grab it and pull.

To test the thermostat, go back inside the house, get a pot of water, put your thermostat inside and get the water boiling. Get a good look at the fat end of the thermostat, that's the part that needs to retract inside when it gets hot and create a small opening. Once the water is boiling, this is supposed to be opened already.