I drive a 2002 Mazda Protege and it’s been great to me until this past weekend.
I had a 4.5-5 hour trip ahead of me and Google Maps told me a more direct route (i.e. not using the interstates) would save time. It must have erroneously assumed that the highway comprising basically the entire trip would be speed limit 55-65 the entire way. Instead, I found myself slowing down to stoplights and stop signs in small villages between 15-minute sprints.
At some point, the interior heat stops - the air being pulled in from outside is not being warmed at all, no matter what settings I fiddle with. Not long thereafter I notice a rattling noise behind the dash. From inside the car it sounds almost like an animal skittering around in the chassis - irregular, short and clipped. With the hood up and an ear to the engine, it sounds like a piece of plastic fluttering in the wind, but with a faint electric “crackling” quality.
Soon thereafter the check-engine light illuminates. Before long the engine overheats and I pull over to the side of the road. Nothing appears to be leaking, and the crackling sound is the only thing noticable. Being in the middle of nowhere, I jumped back in and proceeded to drive at about 35-40, which was warm on the engine but enough to get me to a small town.
At this point I checked the coolant reservoir and it was empty. Bought some from Wal-mart, poured it in, and headed out. Things looked fine at first since the engine had sat cold while I was running errands, but pretty soon it was overheating again at speeds as low as 30mph.
After getting it towed to my destination, I took it to a garage the next morning. They couldn’t find anything wrong with it, and indeed when I drove it back to the hotel that morning the engine behaved normally, the check-engine light was off, and the interior heating was functioning properly.
The next morning, when it was time to depart (but again after an entire night of sitting in the cold), a 20 minute drive to breakfast was smooth as before. Thinking that the mechanic had either waved a magic wand or I’d gotten extremely lucky, I hit the highway and did 65 for a good 20 minutes until the engine began to overheat again. Slowing down to 45 bought a few more minutes to find an exit, but eventually I had to pull over.
Popping the hood, I notice the coolant in the reservoir is bubbling to the top! Thinking the mechanic might have added more and overfilled it, I cursed him in absentia. After a good fifteen minutes of cooling off, the coolant settled and in fact drained the reservoir entirely; I refilled it to the line and, again being in rural snowtopia with few options, decided to hit the road again.
Not wanting to tempt fate, I stuck to 55mph and the car ran fine for an hour and a half (with the interior heat blasting, per a friend’s advice). I stopped once to check the coolant and all was as it should have been - just below the line I’d filled it to earlier.
Closer to a city, I decided to experiment again and took the speed up to 60mph. This was great for 20-30 minutes but eventually the engine began overheating ever-so-slowly and I had to pull over, let it cool off, and replace another full reservoir’s worth of coolant that had disappeared before I kept going.
I drove the rest of the way home going no faster than 55mph and stopping on occasion to check the coolant. It overheated once even while doing 55mph, but a 15 minute break + coolant refill bought it the rest of the trip.
In summary: Although not 100% correlated, going faster than 55mph seems to trigger the engine overheating, at which point the rattling noise appears and the coolant begins to bubble its way back up the reservoir (like it’s boiling?!). I’m not sure how the coolant is disappearing because I’m unable to find any leak, nor is there any extra exhaust that would suggest it’s burning.
Anybody have a diagnosis for me before I sacrifice my student loans to a mechanic?
Overheating like this could be caused by a faulty thermostat (cheap), a partially clogged radiator (not nearly as cheap), or inoperative radiator cooling fans. If there is a connection between the overheating of the mode control (meaning the control for the A/C, Heat, DEF, etc.) then you need to verify the fans are operating when the mode is in the A/C or DEF positions.
Those noises you have been hearing are not good. The crackling is likely overheated exhaust system shields. The rattling is far more serious and that is likely detonation caused by a seriously overheating engine. This will destroy an engine if the overheating doesn’t.
Another possibility is a weak cooling system pressure cap that is allowing loss of coolant. Eventually the coolant level gets low enough to cause overheating.
Hope that helps.
You might raise the hood and make sure the fans are running with the mode in the A/C and DEF positions. If they are, then install a new thermostat. These are cheap and should be replaced every 3 or 4 years as normal maintenance. (Unfortunately, that is seldom done and many an engine has been barbecued over a 5 dollar part.)
Mazda overheating, does it have over 80,000 miles on it? If it does open your wallet or put a bullet in it. You state it over heats when travelling over 60 mph, at that speed air flow is high enough your fans may not be running any ways. Thermostat being stuck would not let coolant recovery from the catch can, sounds like bad radiator and head gasket.
about 96k on it 
MANY if not all vehicles today need to have the cooling system BURPED of ANY AND ALL AIR before you go back on the road. You can start at a thermostat replacement which is easy to do and inexpensive. Then move to the coolant…if you are adding coolant you MUST burp the system or you will have the same issues you are seeing. Telling me that you had NO HEAT is a DEAD GIVEAWAY OF AN AIR POCKET!!! NO ifs ands or BUTTS! I have remedied more of these issues than I can possibly count.
The usual scenario is someone gets a new thermostat after a slight overheat issue. Fine…Great actually. Thats the first thing you should do besides checking coolant level. Now after the new thermostat…you still have a problem. THIS IS DUE TO THE AIR POCKET CREATED AT THE THERMOSTAT CHANGE. IT MUS BE REMEDIED before any more diagnosis can continue.
If you know for certain that there is no air in th system you have a new thermostat and you still see a problem…then we move on to head gasket problems…not fun, not cheap, you dont want to go there.
Its almost impossible to diagnose this issue from the internet, but I should be able to get you close to the cause. The noise you heard may have been the water pump bearing! due to insufficient coolant level…then you have to ask…where did the coolant go? If this happened out of nowhere you migh have a head gasket problem…I hope you do not. I need more info on this to properly diag your problem.
I have not had the thermostat replaced, but will follow the rest of your advice if I do and it continues to be problematic. I’m not sure how the thermostat improperly displaying the temperature would result in the engine actually overheating and the loss of interior heat, though.
I hope it’s not a head gasket issue, too. A car-literate friend had also suggested the rattling noise might be from the water pump or a loose hose fixture.
This is because you are confusing the engines THERMOSTAT and the Engines TEMPERATURE GAUGE.
They are two different but related parts. The Thermostat controls the flow of coolant through the engine and the radiator. The temp gauge reads the temp of the coolant.
WHen you get no heat OR get no reading on the temp gauge…this means that you have an air pocket surrounding the temp gauge sensor…i.e. it will be in air…instead of submerged in coolant.
If you have no heat that means there is no coolant inside the heater core which is basically a little radiator. If you have air in there…you gots no heat.
DO…this. Get a new thermostat in the engine. Its cheap and easy to do…you can do it yourself with a simple tool set actually (most times) After your new thermostat you must PROPERLY fill the coolant system…then test. 9 out of 10 times you got the issue solved. If you continue to have cooling/heater issues then you begin to open the lovely chapter of head gasket malfunctions…I am well versed in each and every chapter…YAY for me right? 25 years doing this I have seen quit a wide array of issues…I should open another shop… I think I might if I cant get back into my IT career that I have been in for the last 12 years. LEt me know if you have more questions and I will be happy to help.
The thermostat does not have anything to do with the temperature gauge on the dashboard. That is the job of the temperature sending unit.
The T-stat only serves to obstruct coolant flow through the radiator until the engine temp reaches a certain point. (generally around 195 degrees)
The lack of interior heat would be due to loss of coolant. The coolant level only needs to drop a few quarts for this to start happening.
If the T-stat sticks open then the engine may take a long time to warm up and fuel mileage may drop. If it sticks closed then the engine can overheat very quickly. If the T-stat has just flat gone stupid then it can have any of the symptoms above at any time.
The rattling is not likely the water pump or anything to do with a loose hose. This falls back to a badly overheating engine and detonation.
Yes OK4450 has another good point about detonation when the engine i very very hot. Lets hope you didnt get her that hot yet… The more overheat events you have the more likely you will a head gasket failure.
There is a cheap and permanent Hed gasket repair in a bottle. Being a mechanic I would fix it properly by removing the head, but you should know that a $60 bottle of Blue Devil WILL PERMANENTLY repair a head gasket failure…so keep that in mind, there is still hope of a low cost fix even if you get to Head Gasket Land. Properly and mechanically fixing the head gasket involves removing your cylinder head and going to a machine shop to have it cut…then you install a new gasket…and then a new timing belt kit and water pump if it is driven by the T-belt…etc…This is the proper way but it will be very expensive to someone who must rely on a auto shop to repair it…Click and Clack call it “Boat Payments” I hope you do not get there, but I had to mention that there is a fix in a bottle if all hope seems to be lost…
You probably had a minor coolant leak. When your car started blowing cold air, it was because so much air had gotten into the system that the coolant was no longer circulating through the heater core.
If you had let the car cool you could have removed the radiator cap and filled the radiator with coolant then the reservoir.If you had done that, then driven to a repair shop you probably could have saved the engine.
By continually overheating the engine you probably now have a blown head gasket and bearings that are being eaten by coolant. The repairs may be more than your Mazda is worth.
The very first thing to do is replace the radiator cap. It can cause all your symptoms. Then look at all the other suggestions. In addition to the thermostat and the water pump, it could also be leaking from the rubber seal between the radiator core and one of the tanks. That leak can sometimes be hard to detect as the coolant can evaporate so quickly, but it soon leaves a telltale line of deposits around the leak.