Heat not working until on freeway

[jblaze213]

I've got a 2006 Yukon Denali and it's got 40,000 miles. It's gotten cold where I live and defrost is needed in the mornings.

The problem is that the heat doesn't work until you get to the freeway and hit 60 mph. I can warm the car up before leaving and it doesn't make a difference. It just blows cold air until freeway speeds.

Any advice/thoughts? I'm not sure where to begin.

Thanks in advance.

 

[Snorkohl]

Basics first

I am new to this forum, just purchased a 2007 Tahoe LTZ, and looking over other issues and tricks you guys have come up with. I had a BMW that would act the same way, check all the simple stuff first. Antifreeze level, radiator and expansion tank, I am assuming thermostat is working otherwise your temp would be off the chart. Sometimes air gets in the system, and has to be bled off. Heater core could be plugged also, but if you get heat at freeway speed, that is unlikely. I am also assuming you have electric fans that are controlled by a thermostat, make sure they are not coming on until they are required. I like the simple stuff first because it prevents the "I can't believe I didn't check that first" scenario. Just my humble advice, good luck.

 

[jblaze213]

A quick update to my issue:

Turns out my coolant level was low. I bought some DexCool and filled it up 50/50 with water and it started working immediately.

 

[NJTahoe]

I just picked up a 2001 Tahoe and the heat was barely working and I thought it was that it was low on coolant. I filled it up this morning and now it's not even remotely warm air coming through. I double checked to make sure the AC wasn't on and even when I jumped on the highway it wasn't blowing out warm air. It honestly feels like I have the AC on instead of heat now. The lower radiator hose wasn't warming up and only one of the heater core hoses was getting hot.

 

[dstadnick]

NJtahoe -- I am having the same issue but i noticed the engine isnt warming up to the half way point where the temp gauge usually sits. It will warm up once i get on the highway though. Would this be a thermostat problem?

 

[NJTahoe]

Well I spent the day last weekend flushing out the coolant. I replaced the thermostat and ran some cooling system cleaner through the system for a while and flushed out the heater core. Also the Blend Door Actuator was shot, so I needed to replace that.

Now after a good flush, and new thermostat, the heat is hotter than ever. Run a hose in the system for a while to get all that gunked up dexcool out. It had my heater core completely blocked. Once the cooling system cleaner ran through it cleared some of it out and I was able to run the garden hose through the heater core and it had a crapload of gunked up dexcool come out.

 

[dstadnick]

Thanks man. I think mine needs that as well!

 

[NJTahoe]

Thanks man. I think mine needs that as well!

Good luck with it. Honestly I had it done at pepboys a couple of days prior to doing it myself, and man was I not happy wasting money at pepboys for a flush that they barely did. it was more of a drain and fill than an actual flush. But thats pretty much the last time I go there for basic stuff I can do on my own. The pic above is the gunked up coolant that came out after the pepboys flush.

 

[dstadnick]

Wow! Just did my thermostat and flushed the heater core and it looked nothing like that! Im at 250000 km which is around 150K miles so im happy with that