few bubbles in overflow tank...

i just got my mazda in a trade. the po said that it was running a little warm the last time he drove it and he thought the thermostat might have gotten stuck. so when i got it home i drove it around. it got almost 3/4 the way up the temp gauge and stayed there for over an hour driving around town. i didnt think much of it. today i took the thermostat out and it runs real cool. not even 1/4 up the gauge. but when i got home i could hear it bubbling a little in the overflow tank. i checked the tank and it is full to the top. the little hose that hangs in there had a little bit of air blowing out of it. does this mean the headgasket is blown or just overfilled? and i also noticed that it has a new black painted header on it and 3 of the four pipes have the paint burnt off the first foot or so except the 1st cyl closest to the radiator...is that odd or common? thanks!

is there oil in the water in the radiator?

put a new t stat in it see what happens

i took it out because i wanted it to run cooler. there is no oil in the radiator that i can see or on the dipstick

run a thermostat not good to run without one on these trucks. I think stock is 190 or a 195 degree. They should be able to pull it up at any auto parts store there is a 180 degree equivalent. I would think you would want the the coolant to stay in the radiator longer with a 195 degree to cool before letting the coolant flow

do not run truck without a thermo. U have a cast iron block with an aluminum head that is prone to blowing head gaskets anyway.Correct thermo for the truck is a 2 stage 160/180 thermo.it will open a bit at 160 to get heater warmed up im winter,then close again until 180 so truck can warm to proper operating temp.Be sure and install wit the tiny air bleed hole at the 12 oclock position.BJ

How many miles are on the vehicle?

I think you have a blown head gasket.

Or one that is about to go.

If you had a stuck thermostat, that would cause the head to warp from the heat.

You can try to retorque it.

I agree with Tweaker man.check torque on head bolts then worry about thermo if they are all ok.bj

the odometer showes 184,000 mi....i do not have a thermostat in it as we speak and it is bubbling. i will check the torque on them as soon as i get a torque wrench.

I posted this in another thread. . .it bears repeating with regards to your issues. . .