My o reflow reservoir keeps filling with water . I have no water in the oil, no oil in the water, no smoke or steam from the tailpipe and no loss of power....car drives great. It just eventually runs out of water and the temp starts to rise. I even tried the blue devil head gasket sealer , which has fixed a couple old work trucks for me in the past. It made no difference to my cx7. I'm just not sold that it's the head gasket. Please, does anyone have ANY IDEAS on what could be causing the coolant to be pushed into the reservoir other than a head gasket ?

 

You must do the following
No guessing really can be done at least without first:
Depending on the testing results :
Pressure tests the cooling system
Compression test the cylinders
May need to follow up with a wet compression test
May need to do a leak down test
May need to do a cooling system chemical test
Check thermostat housing temperature and compare with radiator temperature with handheld digital temperature gun .


if you do any of this post the results or

take it to a service shop and let them perform the diagnostic testing for your problem

There really is no short cuts.

 

I greatly appreciate the advice....and I agree. The problem is that I've taken it to 2 shops and a Mazda dealer. The first shop started by replacing the water pump, then the thermostat , then radiator, then the coolant temp sensor. They finally gave me back my money and told me to take my car somewhere else....
. The second shop said they thought it was the head gasket. They said I could either approve the head gasket job or approve $375 labor for them to verify it was the head gasket.gasket them what happened if they came back and said it is not the head gasket...and he said that I'd need to approve more labor to see what else ot could be. So I took my car to a Mazda dealership. They wanted to replace the engine. So I cant even get anyone to do an honest assessment on the car. Everyone only wants to work on it if they can make a couple grand off me. . This is the absolute WORST time for this.... All this happened during us moving out of state. So we are in a new state with no working vehicle and not a single shop in Pensacola, Florida will help me. Sorry...just venting.
Let me add this.... I can start the car and let it idle till it runs out of gas and it never overheats or loses coolant. I can drive it for a few miles and the temp stays really low. After a few miles though, if I stop in traffic for too long itll start to overheat or if I drive it for around 15-20 miles itll start to overheat. Like i said though, itll idle in the driveway till it runs outta gas no problem. Is there anything else that could cause this ??? There are no puddles of water ever....never smoke out the tailpipe. Sorry for rambling.... I'm just at the end of my rope.

 

So the shops threw parts not confirmed failed guessing what caused your problem and did not do any of the service I mentioned to determine your problem.

No I posted what needs to be done to find your problem. A certified automotive technicianwill use their choice based on physical observation which procedure best fit to test first.

Btw when you are diagnosing heating issues you cannot go by the gauge on the dash as that may be inaccurate caused by heating damage. Naturally you can confirm the senders for function and a separate temperature diagnostic tool or diagnostic scanner (NOT BLUE TOOTH) to check if the gauge is reading properly. You can also go into the ECU via the OBDII diagnostic connector and see the exact temperatures of several monitored areas of the engine and compare to a physically checked measurement.


ASE