OK so i bought this truck in march of last year with 127k miles on it. it used to pump out the heat hardcore. Now that its cold out here in Michigan, i'm not getting much heat. the colder it is out, the less heat I get. I also noticed that the needle on the temp gauge barely goes up a couple lines when its below 20 degrees outside. I did notice also that for short periods of driving (like 20 min or so) it barely pumps out enough heat to defrost the windows but if I have been doing a lot of driving for roughly an hour or more, the temp gauge goes up a bit. it doesn't get above halfway to the 210 mark. My question is, where do I stand? Do I replace the thermostat as a start and then try to flush out the heater core if that doesn't work?

My buddies and I replaced the lower intake gasket on the engine in june because it decided to go out on me. we flushed the entire system including blowing out the heater core (no chunks or blockages in there so I can't imagine there's a blockage in the core). We replaced the coolant with the universal orange stuff.

I'm freezin here lol. any ideas?

 

Sounds like the thermostat might not be opening properly. I wouldn't go throwing parts into it without diagnosing the problem though. When it gets up to operating temp are the lower rad hoses hot? or are they cold? If they're cold it's a good bet bet the thermostat isn't opening.
Did you flush the system using a proper pressure flush? Or did you just back feed one of the lines to force flush the heater core?

 

i have not checked the lower hoses. thats a good idea. By that direction, I could tell if its the heater core being clogged by feeling the hoses that go to it, correct? Yes we did flush the system. With a garden hose, we put it right to the heater core lines coming out of the firewall and we found no evidence of a blockage. we drained everything we could from the entire system after we replaced the lower intake gasket and flushed water through it before replacing the coolant and getting air out of the system.

 

OK i'm pretty convinced that its the thermostat not opening properly. I took the truck out on the highway (first time since fall) and after about 10 min of driving at about 70-75mph the temp gague went up and i started getting more heat inside the cabin. Not blaring hot like it used to but definately enough that I had to turn it down a bit cuz I was sweating a little lol. I DID check fluid levels to make sure it wasn't because I was low on coolant and it was just pushing the coolant through because of how fast I was going and radiator and reservoir are both full. I also checked the lower rad hoses. the large one on the left side bottom (facing truck) was not very warm at all but all other hoses seemed to be pretty hot. i'm going to pull the thermostat this weekend and drop it in a pot of boiling water and see how well it opens. if it doesn't, i'll replace it. the truck IS 10 years old and probably has not had the thermostat replaced so its probably about time anyway

 

Thermostat is under $20 anyway, so it's not like it will be an expensive part to replace.
To clarify - Feeling the lower rad hoses will let you know if the thermostat is opening. If they are cold, the thermostat isn't opening properly to allow the coolant to flush back through the radiator. Hence the cold hoses. Quick and simple way to check. If you went for a drive like you said and checked the hoses they should be very hot to the touch (pretty much so you can't hold on to them for long).

 

yup. well like I said. the large hose is cold. I'm replacing it tomorrow. its only $11. even if that wasn't the problem, at least it has a nice new one in there. The hoses for the heater core were not very hot at all. they were hot enough that I could hold them for about 10 seconds before it got too hot for comfort. Thanks for the info Sisk. I appreciate it

 

OK I got the thermostat replaced today. The one AutoZone gave me was NOT the right one. it had a strange shape at the top so i had to go back in mothers car and get the right one... omg wow its so hot I can barely breathe now (yes i'm not that stupid, i did turn it down) Thanks for the idea of checking the lower hoses Sisk.

 

OK so I went to Mt. Pleasant with 15 friends to hit the casino saturday. truck was blazing hot air. On the way back home, my buddy and I noticed the truck was freezing cold (only 29 degrees outside) and i checked the heater and it was blowing cold air... Since the thermostat is a month old, what is the other most likely culprit? Though I suppose its possible, I find it hard to believe the thermostat is stuck since its brand new. Especially since i'm getting proper coolant temp unlike before where the thermometer wouldn't go past 1/4 up before I replaced it.

Clogged heater core? Would (if it can stop working) the water pump not moving coolant cause it? I felt the radiator cap and its not warm at all. Thermometer shows around 180-190 degrees which has been the normal since I replaced the thermostat.

What would be the best way to blow out the heater core when I don't have an outside hose available to use ? (its winter lol)

I should note: When we replaced the lower intake gasket, we did a system flush but we didn't do the heater core lol. I thought we did but my buddy said we didn't. So the heater core is first on my list to look at. (just need to know how to do this in the dead of winter) I am not noticing any coolant smell outside or inside the truck nor any fogging inside on the windshield.

 

From all you have done it seems like flushing the heater core would be a good idea. Just take both hoses loose at the engine. The coolant flows to the core from the hose at the top of the engine so hold the garden hose up to the end of the other hose to back flush.

Do not directly connect the garden hose to the heater hose because if it is plugged you could cause the core to leak. The system operates at about 14-16 psi but most garden hoses have from 40 psi to well over 100 psi.

 

OK thanks for the advice. I fired up the truck before I got out of work this morning and let it warm up and felt the hoses to the heater core. one is barely luke warm, the other is pretty toasty so i'm going to make the assumption its clogged. I'm going to mothers today to flush it out. wish me luck