Except that the OP stated that his temp gauge reached normal and then spiked even higher. That's not a stuck open stat not allowing the system to reach OT. As well, a stuck open T-stat on an OBD-II vehicle will usually throw a P0128 within a few drive cycles.

And no, low coolant level certainly isn't the only cause of no cabin heat. But in conjunction with erratic temp gauge readings, I've found it to be the case every time on makes across the board. But, as I said, a stuck closed thermostat could cause an overheat condition that pushes enough coolant out of the system to create the low condition. I never said his thermostat couldn't be failed.

In your case, it could be a failed thermostat if the thing is never getting warm, though they typically still reach about 170* (depending on ambient) even with the stat completely removed, which translates to luke-warm vent temps.

More likely, if the thing is reaching OT, you either have a stopped-up core or a blend door problem. Check the heater hoses. They should both be hot. Next, verify your blend door operation. If that checks out, try flushing the heater core independent of the system, and try filling it and letting it soak with concentrated radiator flush solvent or CLR for a few hours. If your blend door is working correctly, and both heater hoses are hot, and cleaning the core doesn't work, the core needs to be replaced.

Also, I don't know your repair history, but I've seen more than one cheap heater core with no partition in the upper tank; the coolant flows in and out without ever going through the core veins. After having to redo a couple because of that, I started checking them before install with hot water, making sure the core itself warms.

 

Simple problem, simple fix, let's not overthink it. The OP's problems is resolved, 'nuff sed.

 

A lot of people cruise these boards without ever registering and posting in hopes of finding their answer. I see no harm in hashing out the rest of the potential causes with explanations.

Besides, coonhound130 is still having a problem, and now he'll know where else to look.

 

I have flushed the system and core isn't blocked anymore . But still no heat

 

Did you flush the heater core by itself? Because remember, even with a power flush, the core is pretty much left out of the loop.

I had a Cherokee that was putting out very little heat, even though the hoses were both hot. Flushing the system as a whole did nothing for that. But I did what I suggested you do, twice, once with flush and once with CLR. I let it sit for about two hours each time, then pushed water through it both ways for about 10 minutes each direction. It worked pretty good after that, though it leaked a year later.

But as I said, make sure your blend door is moving, too. While they're mechanically adjusted and tougher than the Ford and Chevrolet units, they still fail occasionally. As do the cable retainers and end locks for the adjuster.

 

I flushed it seperate , also checked the blend door today and it is fine also . I am getting tired of no heat on these 30deg mornings ..