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Drew, Super Mazda Tech.
Category: Mazda
Satisfied Customers: 2518
Experience:  19 yrs. experience. Mazda Senior Certified Tech, with Ford, Linc. & Merc. experience. ASE L1 Advanced Certified Master Tech.
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Mazda CX-7 Sport: Hello - my names Jez and Im the happy owner

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Hello - my name's XXXXX XXXXX I'm the happy owner of a 2008 CX-7. The car has just ticked-off 60k miles and appears to be misbehaving a bit. I have just had what I thought to be an overheating experience on a hot day in bad traffic. Temperature gauge went soaring up and air-con cut out. I pulled over and let it cool down and gave a few things a visual inspection. Coolant in the reservoir (check) no steam / obvious leaks (check), both fans working in the radiator (check) all wheels moving apparently freely on timing belt; no funny noises / loss of power.... Drive on - vents and cabin temp set to hot.....gauge goes up and down like a yo-yo and no aircon (recently re-gassed). Took to garage today and asked for a pressure test of the coolant system - which they did. Pressure in system not just fine, but great for 5 yo car. No leaks. Took it for a spin with diagnostics connected set to look at actual engine temp, aircon compressor, climate control request switch, engine temp and fan state. Inexplicably, engine temp runs steady between 109-116 c, but temp gauge starts racing upwards, aircon cuts out and both fans roaring at the radiator as if the engine is going to explode. What gives? I (my wife and family really) want the aircon back.......but I'm happy to know that mechanically the car is sound and driveable. All help gratefully accepted.
Welcome to Just Answer. My name is XXXXX XXXXX I will be glad to assist you.

Sounds like the thermostat is stuck closed. I suggest replacing the thermostat and then recheck. If the thermostat is stuck closed, the top radiator hose will be hot and the lower hose will be much cooler. I suggest only using a Mazda thermostat that will come complete with the housing and gasket and is sold as an assembly.

Customer: replied 4 years ago.

Hi Drew - thanks for the answer. It is indeed the case that the top radiator hose is hot and the lower one is cool. Does this indicate that coolant is not circulating? The garage felt this was normal. Is that not in fact the case?


If the engine isn't actually overheating - where is the temperature gauge taking its information from and how is this related to the air con? Is there some kind of fail-safe cutting out the compressor?



Yes it sounds like you have a faulty thermostat. If the thermostat Ed open both upper and lower hoses would be the same temperature because the coolant is circulating through the engine. The coolant temperature sensor is located on the coolant housing where the upper radiator hose connects to the engine head. There is a two wire sensor that screws into the housing. If the computer see that the coolant temperature is above normal, it will turn off the AC compressor to help prevent overheating. ThanksDrew
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