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Heater works sometimes, running hot

2016 Chevy Colorado V6. I am having a few different problems and would like some help if possible. I have had either some vacuum issues over the past few months and fixed the purge valve and that fixed most of the vacuum issues for a week or two. Then I noticed in park or idling at a red light the vehicle would feel like it would miss or gargle and shake a little and then return to normal. Almost every day. Then I noticed that every once in a while my temp gage would be above 210f and when I turned the truck off the fan would still run until it cooled down. Then when it turned cold I realized my heater would only blow warm air when I accelerated a lot…ex driving on the interstate. Driving down a 30-40 mph road was not enough to make the heater blow warm air. Any suggestions would be appreciated.

Have you checked the coolant level? That would be the first thing to check. Possibly leaking coolant, getting air into the system.

This wouldn’t explain the miss at idle, however. Assuming no check engine light is on?

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Check engine light was on but resolved when I replaced the purge valve canister. I have not checked anything else yet as the running hot and heater situation really started happening a day or two ago and haven’t had any time to check it since. Plan on doing it this weekend but wanted to get some suggestions first

The radiator fan is working, so I’m thinking the coolant isn’t circulating until the water pump has enough RPM to get it flowing. A weak pump or restrictions in radiator or heater core. Also might consider thermostat could be stuck.

Sounds like your vacume issue was resolved by the new purge valve… so put that issue aside.

Your other problem is a perfect description of air in your cooling system. You cannot have air pockets in the system…it must be liquid coolant throughout.

You do not have an air bleed screw to help burp your system so…if you can elevate the front of your vehicle, like say on a steep hill, it would help this process. When the engine is cold, fill your radiator/remote tank to the top… Start the engine, turn the heater temp all the way to the hot setting to allow the heater core to be involved (important)… and allow it to warm up, you can blip the throttle a few times to speed up the water pump and increase fluid flow, no need to go overboard with this, it does help however. You shouldn’t need to top off coolant during warm up as a little coolant actually overflow when on its way to fully warmed up. THEN… allow the engine to get cold…not cool, cold…and repeat the process. Letting it get cold can take many hours. Also it can take several (3) Hot/Cold cycles to purge out any air that may be in the system.

It’d be nice to have a bleed screw wouldn’t it? Anyway, the Hot/ Cold cycles will burp the system by expansion and contraction of the fluid in the rad and engine in lieu of a bleeder.

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Excellent explanation above from Honda_Blackbird. I would add: collect any spillover coolant and dispose of it with care. It’s poisonous - as in fatal in some cases - to anyone (or animal) that might drink it.

Not every car has a valve to the heater core. Hondas do. It’s a good idea to always put the heater control on Hot so you don’t have to know whether or not your car requires this step to get air out of the system.

Honda Blackburd

Thank you for your help. And the other people who have responded. I’m glad I posted this. I will try this in the morning and let y’all know. Thank you again!!