Ok on the way home from work today my 2002 mazda MP5 started to overheat out of the blue. I pulled over and put water in the radiator and see if i had any leaks and such. I didnt notice any leaks so I went on my way and it overheated again of course so i put the heater on and it was fine and I drove it home, anytime i take the heater off it over heats.

Sooooooo what the hell can it be? DO you think there is air in the system? I tried to bleed it but i have had no success "I dont know how to bleed this system"

The fans come on so that leaves thermostat and water pump which i dont think it is either becuase wouldnt it over heat even with the heater on if that where the case???

Please help!!

 

i was going to say t-stat went bad. but i dont really know.

 

t-stat gets my vote

 

I am leaning heavily towards that since there is no oil in th radiator or coolant in the engine, I just wonder why does it run normal with the heat on????

 

i cant answer the question. but i can say only buy an oem mazda replacement t-stat if you get one.

 

I wonder if its a big deal for an MP5 I know dealer is the only way to go for the 7

this is funny I am going to have to depend on the rx7 till saturday the daily driver is officially shelved.

 

You don't need a t-stat in Davie

 

well its a newer car with sensors and stuff so i will just be safe and replace that sucker. I do remember the olden days when you could pull that bad boy out and run wide open.

 

did the coolant leak out?? if so it could be your water pump....

 

no. once i turned the heater on everything was fine and i drove a good 15 minutes with no problems (beside sweating my *** off from the heater blowing full blast)

 

I don't know about Mazda piston engines, but since 1998, GM V8s have the t-stat on the lower radiator hose inlet. When the t-stat is closed, the pump is still working and only circulating water between the heater core and the block. GM engineers designed it this way so that your heater will heat up much quicker in the winter. If the engine is <180*, the t-stat is closed, but your heater core will still warm up.

 

yep, pretty much all vehicles after 98 did that to also keep cool temps inside cabin when a/c is on, they saw that hot coolant traveling thru the lines into the cabin afected the a/c, so making this minor adj of the bypass t-stat, all was good, unless the t-stat goes bad

 

My t-stat is on the lower radiator hose, so what you are saying is that the t-stat is stuck shut closing of access to the engine from the radiator causing the overheating and by me turning on the heater it starts up the fan on the core circulating hot air into the cabin and just by happenstance cooling off the heater core which in turns cools the water going back into the block.

Makes sense now. I hope it is that and nothing else.

 

sounds like the cooling fan on the rad isn't working. with the engine running, set the climate controls to A/C and look and see if the rad cooling fan is running. it should run constantly with the A/C on, provided it only has one fan. the early 90 caravan has 2, one on the rad and one on the condensor. if in fact the fan has stopped working, it could either be the relay or the fan motor. and this is why running the heater blower will partially help cool the engine.

 

nope fans run fine both of the. pretty sure its the t stat

 

Right, it's basically turning your heater core into your radiator.