2011 Mazda3 iS 2.0 keeps overheating even after many repairs!

Help! I can’t afford to spend anymore money on this car. I had this car less than a month when it overheated on the highway coming back from out of town (I had already driven the car hundreds, if not thousands, of miles by then with no problems). I was told I had a blown head gasket. A mechanic (who I will simply say was not equipped to deal with this problem) tried to fix it, but I doubt he did more than replace the thermostat and the water pump. The car overheated 5 min after getting on the highway (and the check engine light came on again). That mechanic and I did not part on good terms, and I had to go get my car back. Another mechanic diagnosed it as a blown head gasket and then never called me again. Third time’s the charm right? Well…no. Third mechanic took the head to the machine shop after finally diagnosing it as a blown head gasket and saying two cylinders weren’t good (only after saying it was fine and that it simply needed to be burped, and having it overheat again). The machine shop said the head was still good and shaved and glazed it. Two cylinder springs and the head gasket were replaced. The mechanic calls me yesterday and tells me the car is ready; he drove it with no overheating problems. I asked if he had driven it at higher speeds and he said yes. Again, 5 min after I drive it over 60 its overheating again. The mechanic picked it up and is attempting to figure out why its still overheating since he said everything was done that should have been done. His next guesses were a damaged CAT or the fan. I read on another thread that it might be a clogged radiator or simply the radiator cap. Is this likely? I don’t know much about cars so I have no ideas. I bought the car from a “friend” of my dad who got it at an auction and I didn’t do my homework. Its got almost 80,000 miles and there was no warranty. Any suggestions?

Update: CAT, radiator and radiator cap are fine. He says it has to be a problem with the engine and is taking it apart again.

I think your model uses a single radiator cooling fan. With the engine up to operating temperature raise the hood and allow the car to idle.
Turn the A/C on. You should see the fan running whenever you do this.
Turn the A/C off and allow it to keep idling. You should see the fan randomly cycle on and off as engine temps climb high enough.

If this overheating only occurs at highway speeds (and assuming fan operation is fine) that usually points to a clogged radiator or possibly a missing lower radiator support airdam if so equipped.

The radiator cap could be a cause if it’s weak and popping off now and then and which leads to engine coolant being burped out of the system to the point where it’s low enough to cause overheating.

The part about cylinder springs (which I assume to mean cylinder head valve springs) sounds odd as bad springs would be highly unusual on any make of car with only 80k miles on it. I could think of several reasons why those springs would be bad; severe overheating or a snapped timing belt at one time.

A partially clogged catalytic converter can cause overheating but that can be easily checked with a vacuum gauge.
WIshed I could be of more help.

Thanks. He did check all of those and said they are fine. He said its in the motor. We’ll see.

How many miles? Head was checked for cracks?

It sounds like the mechanic is trying their best to get to the bottom of this. Probably best just to follow along what he does.

Here’s some ideas

  • Maybe the engine isn’t overheating. Maybe the dash gauge display is wrong.

  • Water pump could not be pumping enough.

  • Thermostat could be non-functional or positioned incorrectly.

  • Try another known good radiator and cap and the cat bypassed as a test.

  • Do the various tests mechanics know how to do to check for leaks between the cylinders and the coolant chambers, cylinder leak down tests, cooling system pressure tests, pH tests of the coolant, etc.

  • Make sure the ignition timing is correct.

  • Make sure the valve timing is correct.

  • Air pocket in cooling system.

Sadly they missed a hairline crack in the bottom half the first time they took it apart. Found the problem. Thanks for the suggestions though.

So is the crack in the engine block?