heater blows colder air with higher fan speed, hot air on low

[whysohigh]

My heat is nice and hot as it should be when my fan is on low, but if I try to turn it up it gets cooler and eventually it seems near outside temp regardless of outside temp. Any ideas?

[zieg85]

Compare your 2 heater hoses, both should be very hot.  Is your temp gauge working and reading like it should...  A thermostat that is opening to soon would cause that or a heater core that has restrictions(plugging up).

[bd]

I agree.  Your heater core may be partially plugged with sediment.  Feel the heater hoses as close to the heater core as possible, with the engine running and heater fan on high speed, to see if the 3/4" outlet hose is significantly cooler than the 5/8" inlet hose.  The hoses should be close to the same temperature with the outlet only slightly cooler, if even discernible.  If there's a significant difference in temp, the core is plugged.

[whysohigh]

Ok so I pulled both lines going to the core and stuck the garden hose to it full blast. I got nothing but a nice strong stream of clean coolant out the other end. So I found a spare thermostat I'm going to stick in. I've only owned this truck for a few months so its possible it had a bad t stat or even none at all. I'm a little scared to see if it has none because no one just takes out the t stat for fun.

[whysohigh]

Also forgot to mention the temp gauge wasn't working and I found the disconnected wire hanging, as I was attempting to re connect it I had a friend in the cab with the key on and everytime I touched ground the gauge went crazy so that's my indication its working. I would test drive it but then I would have to wait for it to cool to do the stat. Keep you all posted.

[zieg85]

Ok so I pulled both lines going to the core and stuck the garden hose to it full blast. I got nothing but a nice strong stream of clean coolant out the other end. So I found a spare thermostat I'm going to stick in. I've only owned this truck for a few months so its possible it had a bad t stat or even none at all. I'm a little scared to see if it has none because no one just takes out the t stat for fun.

Maybe not for fun but I've found my fair share missing over the years and found no issues when I installed a new one.

[whysohigh]

I pulled the t stat and it was mangled, looked like someone hit it with a big punch and hammer, or a .22 test drive coming once the sealant is dry.

[whysohigh]

I've got heat and a temp gauge, thank you guys. You never know what you'll encounter when working on a vehicle someone else worked on.

[zieg85]

Good news, heat is a wonderful thing

[bd]

...especially this time of year!   

[whysohigh]

Indeed, especially here in Michigan