Hi all, just joined the forum. My wife drives a 2007 SE we bought brand new, now around 105K miles. We've had zero issues with this truck. It's driven us cross country and then some, up and down the mountains more times than I can remember. Daily driven, though no towing, and no off roading. And since it's not mine, it has no mods either.
We haven't had any issues with the trans/coolant contamination either, thankfully. However, since I've been on the forums the last few days for this heat issue, I've already ordered the part to do the mod ASAP.
Anyway, onto my question. My wife normally warms the truck up on cold mornings; it starts cold, gets up to operating temp, at which point the heat gets hot, and by the time she gets out there the cabin is warm. It has worked like this since 2007. All of a sudden this winter the cabin isn't warm when she gets outside. The air blowing out is cool regardless of how long it's been running. Temp gauge is at the normal spot. As soon as she starts driving to work the heat gets warm and it works fine thereafter.
I started with the "burp" method I found online to remove air bubbles. Hand in hand with this I also added coolant, as it was indeed low. Results from this were hotter air when it was hot, but it didn't fix the idle issue.
Next I replaced the cabin air filter, which was definitely dirty. Results were a perceived 100% increase in volume of air out of the vents. However, heat at idle when started from cold was still cold.
Next I drained the coolant, did a flush with a Prestone flush solution, followed by another water only flush, followed by all new coolant fill. This included the run 10 mins, run the heat 10 mins, cool down cycles for each. (I painted the trim on the house during the downtime...) The hope here was if the heater core is/was restricted or blocked that it might clear out. Still didn't fix it.
Today I went out when she started it and sat in the cold with my coffee and watched the temp gauge. It took its time getting to op temp. I gave it some gas to speed the process, and when it settled out I turned the heat on. Cold air. Gave it a few minutes, still cold. Then with my hand in front of the vent I hit the gas up to 2 or 3K RPM and released. Instantly the air got hot. And stayed that way! Interesting data point.
Today I changed the thermostat. Thought I read you had to remove the fan shroud, which took most of my time, but when I came back inside realized the manual didn't say that. Oops. Made it WAY easier to get to the bolts of course, so whatever. Learned how the whole front end comes apart and goes back together! Anyway, I thought maybe the tstat was stuck open. I didn't have a solid case for this, but I wanted to rule it out. Upon removal the old one was in fact closed, and a little corroded under the lower hose where it might have had a very slow leak. Put the new one in and buttoned it all back up. Same results as this morning. Cold air prior to and after op temp. For a while. Then as soon as I hit the gas it got hot.
So...what else can this be? I'm thinking the heater core could still have a blockage or restriction that requires a surge of pump pressure to get the hot water in there. But the coolant that came out looked pretty clean, so corrosion seems unlikely. I'm leaning more toward a valve that is stuck, or a sensor that is waiting for RPM, but I'm not sure if either of those are real things.
One question I do have for you guys (yes a picture will be better, but I'm inside and it's cold out there) is what that pump looking thing is in the hot water line that goes to the heater? If you're looking under the hood, on the driver side there's a hose that comes out from the head and goes aft and up to a round box near the firewall. Another hose comes out the side of this box and then runs behind the engine and into the heater core. There is a wire harness coming out the top of the box. Somewhere I read that this is a booster or auxiliary coolant pump, but I cannot find evidence of this thing ANYWHERE. Seems like a very likely culprit to me. I'm considering removing it and connecting the hoses with a nipple just to see if it fixes the idle problem. Then I'll go about finding a replacement part!
Anyway, any help or suggestions would be great. This is not a life threatening issues, especially since all she has to do is pop outside after it's warm, hit the gas, and go back inside! But I hate when things don't work right...so I want it fixed.
Thanks in advance!