Ok this is the problem what do i need to write in the ODF so that the weapon can Owerheat ?

Change the ammo for the person you are giving it to to 0
Then go to a pistol odf and open your odf and find somthing that says overheat time and put it in your odf in about the same place as it was in the pistol odf

What he means is Change the rounds per clip on the weapon you're editing to 0, then look in the .odf of a weapon that can already overheat for a few lines that say something like

HeatPerShot = "number"
HeatThreshold = "number"

And other things that have to do with heat. Copy those lines into the odf for the weapon you're editing and mess with them how you like, the weapon should now overheat.

Yeah, what he said

HeatPerShot, HeatThreshold, HeatRecoveryRate.

No offense dude, but is it really that hard to look in com_weap_inf_pistol in the Common side folder?

Do i really need to change the ammo count to 0 because i don't want a LMG with infite ammo

No, but along with having overheat rates, you'll also have to worry about ammo.