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Overheating Mazda3

Last weekend we noticed that the engine temp was spiking. I still does. Sometimes it’s a matter of just 8 blocks of driving before it’s up, during which the heater doesn’t want to blow hot air. Or, it will have a normal operating temp around town, and then start to spike when we hit the highway, and the heater works fine then (it even seems to take some of the temp off of the engine, like it should.) I took it to Autozone to have them run codes and it came back with a faulty coolant temperature sensor (I don’t remember the CEL code.) I have the replacement sensor and can replace it, but I’m not convinced that this is the problem anymore. Yesterday I had the coolant flushed, but I still have overheating issues. In fact, it seemed to be worse on the ride home from the coolant flush. Anyway, I noticed riding back from Autozone today that it felt like the engine was braking, as if my car were a manual. Now, I’ve ridden a few manuals before, and the braking I felt wasn’t as heavy as the braking you feel when you release the accelerator and the clutch is still engaged, but it’s similar. I think I’m a little overdue for a transmission fluid change. Could that be it? Any thoughts?

My Mazda3 is a 2008 automatic with the smaller engine. It’s stock.

Do the fans come on when it overheats?
I wonder whether you don’t have an airbubble in your system or maybe a blocked radiator.That’s kinda what it would do. Flushing a system is all good and well but it can be difficult to remove air bubbles. Often you have to take the top radiator hose off the engine and fill it from there to minimize the chance that bubble forms.

The transmission acting weird could be an unrelated problem, of course, but it does need to be cooled through its own core that’s part of the radiator (I think that’s true of Mazdas, anyway).

Try the cheap things first:
To burp the airbubble out, park your car slightly uphill or on ramps. Wait for it to cool so you can open the radiator cap and start the car. Rev it a little and notice the neck of the radiator. Watch it drop level and burp air bubbles. When it drops and doens’t really come back to the level it was, , add some appropriate coolant. When you stop seeing bubbles, close it up and see what it does.
Mazdas may have a valve you open on top of the engine to let the air out but I like old school burping.

Don’t let it overheat, though. Be careful as that can do lots of damage.

Okay, so I did two things since. I replaced the coolant temperature sensor. I also did the burping. I still get overheating. It seems that I am fine, with the heater off, in town. I can go 30-35 for a while without the temperature spiking. As soon as I hit the highway and start to go above 40, the temperature spikes withing 30-40 seconds. Then I have to stop, let the car cool down and then slowly pace back into town.

I plan on swapping out the transmission fluid this weekend (it needs it anyway.) Any other ideas?

All good ideas above. Here’s my two cents.

Assuming all the routine engine/xmission maintenance is up to date, and all the engine cooling fans are working and the coolant is a fairly fresh 50/50 mixture and the radiator is full. And that all the DTC’s (codes) current and pending have been read.

In my car at least the coolant temp sensor is used by the engine to computer the air/fuel mixture, and if it failed it generally wouldn’t cause the kind of overheating problem you are experiencing. But it might cause the engine to run poorly. Or display the temperature on the dash guage incorrectly. Assuming the engine is actually overheating on the freeway and it isn’t a guage/sensor/display problem … hmm … well, a faulty thermostat and/or water pump should be considered. If either fails, it could affect the heater as well as causing engine overheating.

Unlikely to be the transmission, but possible. To eliminate the transmission as a cause, put the car in neutral and idle it in your diveway. If it still overheats, it is unlikely to be the transmission.

So, I changed the ATF. Still having a problem. It’s weird. It doesn’t overheat when it idles in the driveway. It doesn’t overheat when I doddle around town at 30-35mph. It just overheats when I start to head out of town at 40-45+mph. The radiator fan spins. The only tell beyond the temperature gauge that something is wrong is the sound I hear when I drive. It sounds like a lower pitch siren (the hand-cranked kind.) Also the engine seems to take longer to wind-down after the ignition is killed.

Thanks for the help so far. Really anxious to get this nipped because we’re using the SUV more now and gas isn’t cheap when you drive 200 miles a day.

This behavior isn’t normal and needs to be addressed or it will damage the engine. It could be any of a dozen different problems, so it may take a while to figure out. Make sure to monitor the engine temp at all times until this is fixed.

If this were my car, first thing is I’d probably check the ignition timing; if that was ok I’d put in a new thermostat. If that did’t fix it, I’d replace the water pump. While doing that, I’d check to make sure the timing belt/chain is aligned properly.

Probably the next step after all that is to take the car to a radiator shop and ask them for a diagnosis. You might want to do this first if you have reason to believe the radiator may be on its last legs. Cooling systems are what these shops do every day and they’re usually the best experts at diagnosing and fixing these kinds of problems.

There’s no way this car has a distributor, so trying to check the ignition timing is an exercise in futility.
Why haven’t you changed the thermostat and radiator cap yet? Those would be among the first things to do in an overheating situation.
It’s possible that one of the electric fans has a bad bearing. That might explain the “siren” sound.

Radiator cap. You have all the symptoms.

I agree with OK.
That siren sound being a bearing makes a lot of sense. Maybe you can hook 12V up to the fans to see if you get get them up to speed while you’re looking at them to make sure.
Radiator cap is also a cheap thing to try.

Would the radiator cap hold any pressure if it was no good? Because when I opened it the other day there was definitely pressure built up inside the reservoir.

It may not be holding pressure intermittently. The other guys up there^ are right: the radiator cap is very often overlooked as being the culprit. It is easily and cheaply replaced. Certainly worth a shot. They do go bad.

There is a difference between holding pressure and holding the proper pressure. Caps are cheap.

It also sound like there might be an air bubble left in the system after the “flush”. It might need to be bled again. BTW, what do you mean by “flush”, there are several types of “flushes”, none of which should ever be done.

I’m not entirely sure. It was done at the local quick lube shop. They had a machine that I’ve seen in many other places to do the job.

@db4690 … just curious about the ignition timing comment you made above. I’m don’t have newer car experience, my vehicles are 20 years old and 40 years old and have a distributor and it is possible to change the timing by twisting it. But I thought on newer cars which use the ECM to set the timing, while it might not be possible to change the timing, it is still possible to check that the ECM is doing its job properly by putting the ECM in open-loop mode and using a timing light on the crank pulley to veryify the no 1 cylinder is firing when it should be firing. No?

@GeorgeSanJose where would you connect the timing light on a coil on plug car?

To complicate things further, modern cars can fine tune the ignition timing for every single cylinder.

YULitle, I have long been opposed to flushes of any kind on either cooling systems or transmissions. You have added to my argument, thanks.

Yulite, I’ve long been opposed to getting any work done at a ‘local quick lube job shop’. You’ve added to my argument. Thanks.

Seriously, don’t get stuff done at a local quick lube shop. They are morons.

@db4690 … well I’m learning something here. Thanks for the explanation.

I’d have guessed even with the coil in the plug ass’y the timing light would still trigger. But it must be the case the way the coil/plug is configured, that isn’t the case.

some things to check for overheating? the radiator plugged with bugs and debris, blocking air from flowing thru it? the thermostat opening AND closing correctly? the cylinder head gasket leaking exhaust into the cooling system? (a leak-down test may reveal the problem)…

So, I replaced the radiator cap and had some short success, which may have been nothing. I made it further out of town and it didn’t heat up. I hit an exit and made the turnaround to come back home when it started to heat up at higher speeds again… :confused:

One other thing that might be an issue. I don’t have the black flashing on the bottom of the car anymore. I was looking at the radiator for bugs (it’s pretty clean) and I noticed that there is the big hole where the flashing was. I only bring it up because that gives the air coming at the radiator a way around the radiator screen. Sound feasible?

I’m prepared to try replacing the thermostat next, but just wanted to chime in for some more advice. Thanks for the help so far. I don’t think that I’ll be taking it in for anymore flushes. :smiley: