Mazdaspeed 3 Coolant system gurus

[SpankyStokes]

Ok guys I hope this isn’t prohibited but this is a question about a Mazdaspeed 3 I have. Bought with overheating issues.

My issue is after bleeding the coolant system with the cap off and capping it all my coolant eventually makes its way to the overflow reservoir and stays there then I start to over heat.

Is the coolant system supposed to be breathable ? My overflow tank has a weep hole that I can’t blow thru with the cap on.

 

[gst-turbo]

Is the lower hose cold? Is the thermostat opening or is it stuck closed?

 

[SpankyStokes]

I’ve tried 3 different thermostats. Only time it doesn’t over heat is without one. Also only time it pulls coolant to the reservoir is with one installed. To me it seems as if the coolant system isn’t breathing so it expands to the overflow.

 

[motomattx]

For some reason its pushing coolant, you might just need a new radiator cap or it could be something more sinister such as a blown head gasket, you can check for a head gasket issue with a leak test kit that you can rent for free from most of the big three auto parts stores, that could narrow it down, I would put a new radiator cap on it and go from there if it was me, you might also want to find someone or a shop that has the device to pull a vacuum on your coolant system and refill it that way so as to be sure that there is no air trapped in the system, some modern cars are a bear to get the air out of the system.

 

[luv2rallye]

Ya, pressurize coolant system to check for leaks (like head gasket leak). Check thermostat opening properly or buy a new one. And burp system with rad cap off, engine warm but off, and squeezing the lower rad hose many times (use rag so you don't get burned).

 

[AWD-Tony]

I had a similar issue with my jeep where it would run a little hot in the summer with the ac on only local driving, highway was fine. It would also boil out of the reservoir. Turned out to be the thermostat not fully opening. Is the thermostat a generic from parts store? You can boil the ones you pulled out to see if that’s the issue.

 

[SpankyStokes]

Previous shop said they had replaced the head gasket. I went ahead and redid it anyways and checked the head surface and block with a straight edge. Factory max clearance is .004 and I couldn’t even slide .003 thru the head or block. Had a machine shop check the head as well and it checked out straight.

Reservoir cap has been replaced with a new one. This system fills thru the expansion tank. Coming to the car after it’s cold and the reservoir full. I remove the cap and hear pressure escape and after it’s relieved all the coolant flows back down into the radiator.