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sprinkles08, ASE Certified Technician
Category: Car
Satisfied Customers: 22803
Experience:  ASE Master and Advanced level certified. Factory trained with 15 years dealership experience
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Mazda CX-7 Sport: overheating issue

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i have a 2007 cx7 that i had to replace the engine due to a vvt fail and now it has a overheating issue dont know if its air in the system but the car starts to overheats while driving the temp will go hot to normal multiple times and when i stop it starts to spike but when i rev it to 3000 rpms it starts to go back to normal i have been working on it for 3 days now and it has me stumped also it was a engine from iko

Hello and welcome to JustAnswer!


What you're describing does sound like trapped air in the cooling system. The first thing I would recommend is bleeding the cooling system, which I'm assuming may not have been done when the engine was installed.


With the engine cool remove the radiator cap and add coolant until it is nearly full.


With the cap off start the engine and let it run until it reaches operating temperature. Along the way the level will most likely drop as air comes up, you can periodically top it off if necessary.


When the thermostat starts to open then the level will become unstable, the level will likely come up and it may spit some back, so be careful of the hot coolant and steam and have a drain pan under it just in case.


When the thermostat is staying open and the engine is at operating temperature make sure that you have heat. If not then there is still air trapped in the heater core and hoses, you can raise the RPM's to help force coolant through.


When it's staying at operating temperature, you have heat and no more air is coming up then you can do a final top off of the coolant, install the radiator cap and then drive it to see if that takes care of the overheating and fluctuation.

Customer: replied 3 years ago.

I have done that seraval times but I agree with you that there is air in the system just have been working on trying to get that air pocket out but the weird thing is that it only overheats when you start driving it other than that if start the car up and let it sit and run allday it will never over heat only till after you drive it.

Is there continually air still coming up after repeatedly bleeding it? You may be fighting a leaking headgasket or cracked head which is pushing air/combustion gases into the cooling system continually.
Customer: replied 3 years ago.

see how that's what I think to cause it doesn't seem to stop burping up after the themastate opens I check with my boss when I get to work in the morning and tell him

It shouldn't take more than a couple minutes after the thermostat opens for the air to stop coming. If you're continually getting air then I think you're fighting a combustion leak. You can use a block test kit (available at any parts store) to check for the presence of combustion gases in the cooling system. The kit comes with a clear vial that you place over the radiator cap opening and a colored liquid (usually blue) goes in the vial. You run the engine and if there are combustion gases in the cooling system then the liquid will change color (usually to yellow).
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