IM TOTALY BAFFLED(NEED HELP)

OK OK OK I FINALY ran into a problem that i can fix
ever since i got the truck the heater has been blowing cold air
i just replaced waterpum, timing belt, head gasket, intake& exhaust man gaskets also thermo stat,radiator, radiator cap i flushed it out and im still having the same problem
when the truck warms up it just pisses out the over flow res i have pressured all the lines out looking for a clog. no water in oil good compression i dont know what the freaking deal is
it has never really overheated unless it had a thermostat in in so last summer i just ran with out one but its winter and its to cold to ignore this problem any longer plus if i want to take a road trip i need to get this fixed.
me and my crew are baffled on this any idea would be killer im dumping money left and right into this truck and i have to much money invested to give up
PLEASE I NEED IDEAS

I would think as long as you have flow to the heater core you would have heat . Look up under the dash and see if the cable that runs from the hot/cold switch on the dash it sounds like it might be closed and the cable broke...

If it is leaking water out the overflow tank,truck is either overheating or something is clogged up.be sure u have the right thermo and it is intalled with the air bleed hole at 12 oclock position.did u have the rad pro flushed or did u do it?If it was really clogged up,I would take the rad off and let a pro shop flush it for u.They get crap down in the bottom and it is very hard to get it out.heater may also be clogged up.bj

stupid question...maybe... do our truck have a heater core?

Also check the rad after the truck is upto temp. Turn the truck off and put your hand in the center of the rad and see if its cold then check the top and bottom. I had a problem with a clogged rad tried everything to clean it but nothin worked went and got a new one and it has been fine since. I saw you put a new rad in but not sure if it was NEW or from another truck.

try another tstat i have had new ones that were bad

Maybe bypass the heater core and see if it still pukes into the overflow. If not then you can blame the heater core.

Well I don't think its clogged cuz everything is flowing fine yes. I'm gonna check the t stat again sparky pulled the top hose and flowed water threw the block and no clogs the cable is fine we checked that and the heater coreisnt plugged

The other rad was from another truck but I talked to the guy who taught us how to weld and
He was in the rad business for 20 years and he don't think its the rad but screw it its only $180
For a new one I dumped so much money in this binatch already what's another $200 bones

I would look at the heater core and the hoses to the core. The last Mazda I tore apart the heater hoses, core, and temp valve were completely clogged with what looked like clay. The PO did not use coolant just tap water. I guess tap water here has a bunch of clay in it? Might be something to look at.

Matt