Mechanic help, Heater/Coolant system

[Pete112288]

I have a 2006 Chevy Equinox LS 3.4L. That I just bought a couple months ago.
I had noticed the heat did not put much out. Then I noticed the sound of running water behind the dash when I would take off from a stop or even in park when the RPMs went up.
Part of buying a new vehicle I do a full tune up and some other work. It has 177K miles and so I have been bringing a lot of stuff up to par beyond just a normal tune up.
I drained & flushed the coolant system, new thermostat, and new water pump.
If I work at bleeding/burping the system of air I can get the heat and defrost blowing hot at idle and at high RPMs. However, once the RPMs go up over 25K or so and then drop back down I can start hearing the water running sound again and my heat goes cold. From that point if I keep the RPMs high then it stays hot, but once the RPMs drop, so does the heat.
The running temp of the vehicle never has an issue, it stays within normal running temps.
There is no smell of coolant inside the vehicle at any point in time and it has no other symptoms of a bad heater core.
There is no outward leak of coolant anywhere. Occasionally after a decent drive I can get out and catch a very faint smell of coolant but no idea where the odor is coming from. No steam, smoke, or drips of coolant anywhere.
I took it to a mechanic I trust and they did a full flush as well and bled the system of air. They said they tried it the "traditional" way and also tried putting the "vac" on it. Heat will get hot and be fine in both vent and defrost, but then after RPMs go up for a moment then back down, it goes cold again.
They checked it out again today and tried a different "purge" as they called it and asked that I drive it a bit and report back to them and go from there. But after a few minutes of driving and RPMs going up, it just went cold again. Whenever I pick up RPMs it will get hot, but go cold when they drop. They also said they checked and tested for a possible issue with the head gasket and they said that is not the problem at all.
Anyone have any ideas or had to deal with this before? I am willing to pay the mechanic, however I am hoping maybe I can find a lead before I just hand it over to them to have to go through it head to toe for their hourly rate.
Thank you for any help!
Oh, and the mechanic also told me that the radiator fans are not cycling on. When the A/C compressor is running as in running A/C or defrost the fan will come on. However otherwise the fan does not come on. The mechanic said he tested all the relays and fuses for it and they are good.

[172ndVet]

That’s crazy. I’m not a mechanic but my brother was having the same issues. Heater not working but his would over heat like crazy. He took it to the dealer he bought it from and they threw parts at it until my brother demanded his money back because of the lemon laws in Colorado.


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[Sandberm]

I'll take a stab at this based on how my 03 chevy s10 is built, but your equinox may work differently.

My s10 also has that water running sound  behind the dash right after the truck is started and when first accelerating. I have no issues with heat however. Ive gotten used to this sound and I dont worry about it. The control knobs for where the air blows and the temperature adjustment run off of vacuum. I'm not exactly sure how it works but on top of the transfer case is a "transfer case switch" with three vacuum lines running from it. One of those lines runs up to the engine compartment on the drivers side to a round plastic ball ( an accumulator) located in the drivers side front fender. It tees off somewhere right before that and a vacuum line goes through the firewall to run the temp/fan control inside the cab.

When the transfer case switch goes bad it allows transmission fluid to enter these lines and it flows into the temp/fan control "module"(whatever you want to call it) that you operate in the cab. The transmission fluid ruins that module and maybe the actuators that open and close to direct the airflow. On my s-10 I would pull the vacuum hose apart at that tee in the engine compartment. If I see red transmission fluid in that hose  then I know that switch is bad.

The other thing that very well could be bad is that those vacuum lines are rotten and are leaking, thus you do not have adequate vacuum to run the temp control. On my s10 one of those 3 lines that run out of the transfer case switch is what engages the 4wd. My 4wd quit working and all I had to do was replace that chunk of vacuum hose to fix the problem.

So, in summary, i think you have a vacuum leak and/or a bad transfer case switch (if your vehicle has that switch like my s-10).

[Timberstalker]

Sounds like a bad mix door.

[Woodchuck]

How did they check for a blown head gasket?

[Smokeploe]

Check the heater hoses, they may either be kinked, or swelledup inside.  Hosed with a lot of time on them can do different things.  Most of the time the swell up, puff up, or collapse.  I have had radiator hose swell shut causing the engine to overheat, everything looked normal. When your rpm go up so does the water pressure, then it pushes past the closed section of the hose.
Another thing check the hose going to the vacuum shutoff valve in the heater hose, the inlet side, also check the valve it could be corroded inside.

[jackelope]

How did they check for a blown head gasket?

 

[Sandberm]

Sounds like a bad mix door.

Google sure points to that direction

[jackelope]

A blend door has no way to cause a gurgling air noise.

The water/gurgling noise is there because there is air in the cooling system.  It’s either losing coolant or there is air being introduced into the system. That’s my internet guess.

[Woodchuck]

A blend door has no way to cause a gurgling air noise.

The water/gurgling noise is there because there is air in the cooling system.  It’s either losing coolant or there is air being introduced into the system. That’s my internet guess.

X7

[jackelope]

A blend door has no way to cause a gurgling air noise.

The water/gurgling noise is there because there is air in the cooling system.  It’s either losing coolant or there is air being introduced into the system. That’s my internet guess.

X7

times 7, huh?
Wow...thanks!

[timberghost72]

Sounds like you have a partially plugged heater core. With a partially plugged heater core you won't get much heat output except when you are reving up like you stated. Also it will make that gurgling noise due to inefficient internal flow.

If true that you are not losing coolant either internally or externally and you are not getting warmer than normal temps then its doubtful it is a head gasket. And if your engine temp did go up due to head gasket your heater would also get hot.

Let your vehicle run for a bit with the heater off tem at low setting and check your heater hose temps. Should be similar.

Then run heater for a bit temp hot. Check hoses again. Outlet hose should be cooler than the inlet.

Start with the basics first.

 

 

[Woodchuck]

Sounds like you have a partially plugged heater core. With a partially plugged heater core you won't get much heat output except when you are reving up like you stated. Also it will make that gurgling noise due to inefficient internal flow.

If true that you are not losing coolant either internally or externally and you are not getting warmer than normal temps then its doubtful it is a head gasket. And if your engine temp did go up due to head gasket your heater would also get hot.

Let your vehicle run for a bit with the heater off tem at low setting and check your heater hose temps. Should be similar.

Then run heater for a bit temp hot. Check hoses again. Outlet hose should be cooler than the inlet.

Start with the basics first.

 

Where does the air to make the gurgling sound come from? A car's cooling system in proper working order is sealed and contains no air.

[full choke]

I am not a mechanic, so take this for what it is worth, but it sounds like this is the part you need:

https://www.oreillyauto.com/flux-capacitor?q=121g

Hope you get things working. I hate vehicle issues.

[Woodchuck]

I am not a mechanic, so take this for what it is worth, but it sounds like this is the part you need:

https://www.oreillyauto.com/flux-capacitor?q=121g

Hope you get things working. I hate vehicle issues.

Pretty sure you nailed it.