Mazda 626 cooling problem

[rogerwa]

Hi I've got a problem that has been vexing me for a few weeks. My daughter drives a 2000 Mazda 626 with the V6. she has been having cooling problems. When she has the AC on or in traffic, it will sometimes bubble over and sometimes will get hot and bubble over. She says that it has bubbled over without the temp going to hot. When it gets hot, she shuts off the AC and the temp comes down.

Here is what I have found.

1) I tested the fans and found one of them to be bad - the AC condenser fan was not coming on and I put 12V to it and it didn't come on. so I replaced the fan unit.

She still had overflow and overheat problems

2) I checked all the hoses and cannot find any leaks. It appears to be bubbling over out of the overflow reservoir tube. I replaced the Radiator cap in the engine anyway as I was thinking that it had premature bubble over due to a faulty cap. No dice..

3) I was driving it once while it got hot and got out to check the second fan (this fan was replaced with the fan unit and does work when power is applied). The cooling fan was not on while the engine was hot. So I started with the fan relays. Once I switched the AC fan and cooling fan relays, the cooling fan came on. So I repaced the cooling fan relay.

Well today she the engine was running hot, but did not overflow, which says to me that the coolant is low.

The coolant has been low before so I just filled it up. In reality, the reserve tank is full but the engine is not sucking it back in from the reserve tank. I checked the hose that goes from the reserve tank back to the block and it is clear and does not have leaks.

I do not think it is the water pump as it will run cool on nice days and even on warm days does not alway get hot. If the water pump was faulty, it would always overheat.

Does any one have history on this vehicle tell me why the coolant would not be sucked back into the block or where my problem might be??

 

[j_martin]

Re: Mazda 626 cooling problem

I know that if the top of the filler neck is nicked or bent, it won't pull coolant in.

There's several parts to a radiator cap. The cap has to seal, the spring loaded disk holds coolant below the neck to a design pressure, and that same disk has a one way valve in it that allows water to pull back into the radiator from the overflow tank.

Any fault in the hose to the overflow tank will also prevent it from drawing back.

 

[puddle jumper]

Re: Mazda 626 cooling problem

It sounds like you may have a sticky thermostat. It would be wise to take it to a trusted shop and have it block tested just in case it has a bad head gasket. The fans not coming on may be due to the air build up in the coolant pocketing around the sensor or bad relay/wiring. Most electric fans will not come on till the engine is about 200/210degF.

 

[bruceb58]

Re: Mazda 626 cooling problem

Kinda sounds like a car I had many years ago. Turned out to be a bad head gasket. Was the car ever overheated badly before all of this started...lets say from a burst hose that wasn't noticed?

She says that it has bubbled over without the temp going to hot.

To me, that sounds like a head gasket.

 

[kenmyfam]

Re: Mazda 626 cooling problem

Agree, possible head gasket or hairline crack in the block.
Thermostat should be checked and/or replaced as needed.
My 2 cents.