Air in coolant system

[cheese9988]

I posted on another forum and haven't gotten far, thought I'd give a non-Chevy forum a try.

2016 Colorado, 2.5L WT with 6-speed

I have air in the cooling system and have been unsuccessful in removing.
There is a gurgle from the heater core and the temperature gauge regularly swings from normal to borderline overheating (240 °F).

• Heater core has the typical gurgle; the upper radiator hose is warm, the lower is cold (40 to 60 °F). This is a reverse flow system.
• I have heat.
• Temp gauge swings from normal to max. Double verified w/scan tool.
• New radiator cap.
• New thermostat.
• Pulled water pump, it's in good shape.
• Coolant system holds pressure @ 20 psi.
• Cylinder compression good (checking for head gasket issues).
• Pressurized coolant system and checked cylinders for misting w/endoscope. No problems.
• Good coolant color, oil is good, no white smoke from tailpipe.
• No loss in coolant.
• Electric thermostat has 12 V and 5 Hz pulse; removing it from the housing, it heats as it should.
• Radiator is ~4 months old.

What I've tried:

• Using a coolant fill kit.
• Filling on an incline using ramps.
• Vacuum bleeding kit.
• Vacuum bleed kit on an angle.
• Leaving ~1 inch fluid above reservoir seam.
• Warming up and checking for kinked hoses.

No matter what I try, I have the same symptoms- gurgle, cold lower hose, and fluctuating temperature.

Thoughts?

 

[Briansol]

I know next to nothing about cars these days...
but it seems like you've tried everything except the electronic pulse that tells the t-stat to actually open. have you measured it at the ecu or bcm? is it actually sending the signal to open?

 

[TurboMirage]

is there a specific procedure in the shop manual for bleeding it? some chevys have a bleed valve somewhere on the block. may just be 90s ones.

 

[cheese9988]

I know next to nothing about cars these days...
but it seems like you've tried everything except the electronic pulse that tells the t-stat to actually open. have you measured it at the ecu or bcm? is it actually sending the signal to open?

There's not much to go on with the electronic thermostats, this is the best I can find: ScannerDanner
In the video, he's showing a pulse of 200 ms, which equates to 5 Hz. It's a pulse modulated system.

With the thermostat out (open load), harness measures:
- Measures 12 V on one side (ground side switched).
- Thermostat heating coil measures 13 Ω

I don't have an oscilloscope at the moment, nor do I have a multimeter capable of measuring duty cycle.
Jumping wires from the harness to a Fluke 115, and the thermostat:
- Draws ~0.8 A, similar to the video.
- I see 5 Hz on the Fluke.
- Center post heats immediately, to the point it's too hot to touch. I think it's obvious it'll perform differently in liquid.
- The ECM throws a code when it's missing; so it can identify its presence.

I can't say with 100% certainty, however, the fact that it heats outside the housing, my guess it's working.

 

[cheese9988]

is there a specific procedure in the shop manual for bleeding it? some chevys have a bleed valve somewhere on the block. may just be 90s ones.

That's something I'll need to purchase.
The forums mention filling the truck on an incline and it'll bleed the air out in a few days; no bleeder screw available.
To your point, my `93 has a bleeder screw at the highest point in the cooling system.

 

[phunky.buddha]

Mount truck to rotisserie, fill and spin? Shake a bit?

 

[Briansol]

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[phunky.buddha]