Within the last week, my heater has basically stopped working. I park outside and typically start the engine and use the defrost to clear the windshield in the mornings. Then when I get it, it's nice and toasty.

Well, last week, that was not the case and the problem continues. The air coming out (heater or defrost) is not warm at all. The temp gauge reads around 200 and fluctuates when driving. I live 15 miles from work and the heat never gets warm.

Is it the thermostat?

This is only a problem when it's cold outside 30 degrees or less.On a warm day, it will burn you out. That leads me to believe that it is not the heater core.

Any suggestions?

 

Sounds like thermostat. Check simple stuff first make sure you have the right antifreeze mixture, make sure fluid levels are correct, belts aren't slipping, make sure the blend door is opperating correctly. And if that is ok, do the thermastat first, its cheeper.If thats not it then your heater core is bad. The fluctuation in temp could be an airbubble in the coolent system or the thermostat is bad.

 

i dont think its your t-stat. but im no mechanic. if its stuck open your truck wont get up to a decent temp and you'ld get codes for it being too cold. if its stuck closed it would overheat. check your coolant mix and make sure your full like mojo said. when was the last time you changed your coolant or flushed your system?

 

Best way to check a T stat: Take cap off radiator, start vehicle, if coolant begins to flow in the radiator instantly, its stuck open, if it doest move for a while then when car is around 180* starts to flow its working fine. Could be a heater core problem.

 

sounds to me like its heater core problem.. undo both lines under the hood and simply try to blow them out with an air hose.. make sure to do this while system is not pressurised and make sure radiator cap is off..

 

Easiest way I know would be to let the truck warm up, and feel the two hoses going to the heater core right at the firewall. If they are both hot, then you know the heater core is good and more than likely the hvac blend door is not opening to the heat position, but if only one hose is hot the the heater core is clogged.

 

Checked the heater hoses last night. One is hot - the other is barely warm. I'm afraid it's the heater core. What I don't understand is that the temp gauge reads really high and then fluctuates to about 200. Maybe it's just partially blocked. Hopefully it can be cleaned out. Can I take the lines loose at the forewall and run a water hosein it to try to flush out the heater core?

It was also about a 1/2 gallon low. So, I suspect it could still have air in the system. I'm no mechanic, but just looking at it, wouldn't the water pump force the air out of the heater core?

It also needs flushing. Looks like a lot of water instead of coolant.

 

If the core is blocked, coolant can still circulate throughout the engine cooling system.

 

Not to stael the thread, but in my truck the heater does warm up quite nicely when I am driving. If i slow down or stop it starts to blow cold. Is this normal? If not what might cause it? My friend thinks it is the heater core.

 

What you described (one line hot and one cooler) is normal. The heater core is a little radiator so if coolant is circulating through it you will get some cooling of the return coolant. If the core is completely plugged, I suspect both lines would be cold (or only slightly warm) as there would be no coolant circulating through them.