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HVAC not working properly

Tiny
JOE BARTOLETTI
  • MEMBER
  • 2007 CHEVROLET EQUINOX
  • 160,000 MILES
The vehicle listed above has a 3.4 liter. It runs warm at idle. But temperatures drop if I rev motor. The A/C works great. In winter, the vents blow cool at idle. But the heat is great on the highway. Above idle speed? I have a new water pump. Coolant is fine. Why do I have a winter issue (cold) and summer issue (warm)? I have done head gaskets on three other of these vehicles. That's my hobby. Is it a radiator issue or a head gasket issue?
Both cooling fans run fine. It has a new thermostat. I have been driving it this way for 2 years. I really want to sell it and would love to fix it for the next buyer.
Replace serpentine belt and tensioner? I have not tried to flush the radiator. Issue shows up at idle only. Great A/C all the time. Moving or stopped. Great heat while moving. Lousy heat at idle.
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Sunday, April 24th, 2022 AT 8:10 AM

13 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

Based on what you described and what you have already done, it sounds like there is a restriction in the coolant flow. I would start by power flushing the radiator and the engine block. I don't think there are any issues with the heater core since it works normally once you are off idle.

In this case, I would drain the coolant and remove the thermostat and radiator hoses so you can flush through the block.

Here is a link that gives a general description for flushing the cooling system, but in this case, I would remove the thermostat, reinstall the housing, and power flush through the block. Also, use a good flush product from a reputable company such as Prestone.

https://www.2carpros.com/articles/coolant-flush-and-refill-all-cars

Let me know if that takes care of the issue.

Joe
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Sunday, April 24th, 2022 AT 7:22 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
I side with the flow issue. I, uh, have a very slight coolant smell if I run heat. Carpet is dry. No coolant used in 2 years. I was going to try a pressure test but wonder if it would be inconclusive with heater core “leak”? I got car 2 years ago with hot motor message on dash. The seller feared head gaskets and sold it. Turns out the thermostat was stuck open. I had code for cold motor and hot motor. 0118 and 0128? Seems GM gives you “hot” code for stuck open thermo. To kind of poke you to fix thermostat. Maybe it’s a waste fuel/emissions thing? I think the seller added stop leak as fix. Maybe? And the A/C won’t work with p0118.
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Monday, April 25th, 2022 AT 8:56 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

I have seen many issues with the powder-type aluminum sealer. If you told me the car ran hot both in the winter and summer, and that heat wasn't available, then I would suspect a thermostat issue. But what you described is on both ends of the spectrum. That's why I am thinking there could be a restriction.

As far as the thermostat code is concerned, it will let you know if the operating temperature isn't reached within a specific amount of time. It's exactly what you thought. If it doesn't reach operating temperature soon enough, it produces more emissions.

The P0118 indicates the ECT sensor circuit is high. That should cause the gauge to read cold or indicate it isn't reaching operating temperature.

If your scanner has live data, I want you to check something. After the vehicle sits for at least 8 hours, I need you to compare the ECT temp signal and IAT temp signal. They need to be within 27F of each other. If they are off, it would create issues.

Let me know what you find.

Joe
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Monday, April 25th, 2022 AT 6:13 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
ECT is 48F. IAT is 50F. Been cool this week. The minor heatercore leak is not an issue?
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Tuesday, April 26th, 2022 AT 6:07 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

The slight coolant leak shouldn't cause the issue. The only way it could is if it was low on coolant or wouldn't allow the system to pressurize. On the other hand, I don't feel it would make it run on the cool side.

Your sensor readings are perfect. I don't see any issue with them.

I have a feeling the best thing to try is flushing the radiator and the block. I attached the diagnostics below for the P0118. Take a look through them and let me know if you have questions.

Take care,

Joe

See pic below.
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Wednesday, April 27th, 2022 AT 6:06 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
I flushed the system. According to dash gauge it’s more stable. The code reader says coolant hovers around 200 while driving. At idle it slowly creeps to 212 and fans kick on. Then the temperature drops. Per code reader. But dash temperature needle is rock steady at “normal”. It does not rise at all from 205-212. It’s like dash is saying it’s not changing while code reader says it is. So, is it better than before? It’s 70f air temperature. I have not tried to see if my dash heat issue is fixed or not.
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Sunday, May 8th, 2022 AT 6:12 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Joe,

That sounds like it is working perfectly. I'm glad to know it and thanks for the update.

If you have a chance, let me know if the heater is working correctly now. I'm interested in knowing.

Take care,

Joe
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Sunday, May 8th, 2022 AT 7:17 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
Drove it today. Now the temperature needle is staying a tick above 1/4. Usually between 1/4-1/2. Code reader says all is well. 212f fans come on. Drops to 205. Driving the temperature stays around 200. I eventually turned on the A/C and the temperature dropped even more. To 195. I sat in the driveway for 10 minutes and the vent heat stayed hot. Did not go to cool like during winter. I don’t know. I changed cluster 2 years ago due to crazy tach. Would read 1,000 then 4,000 then 8,000. Maybe my “new” used temperature gauge is flaky?
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Monday, May 9th, 2022 AT 4:22 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
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Hi,

Anything is possible, but the readings you are seeing are perfect. You couldn't ask for it to work better.

I didn't realize the cluster was replaced with a used one. It is possible that is the issue.

Let me know.

Joe
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Monday, May 9th, 2022 AT 6:44 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
Temperature gauge seemed okay, until yesterday. Car is possessed. That’s why I got it for $500.00 two years ago. The ABS light comes on then serv trac control and Stabil Trak is off. Code said right front wheel circuit. New wheel bearing and light came back in 2 days. Done that for 2 years. Next drive and lights are off. I think that could be due to bad EGR. Had a similar issue on another Equinox. New EGR fixed it.
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Tuesday, May 10th, 2022 AT 7:31 AM
Tiny
JACOBANDNICKOLAS
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Joe,

Did the temperature seem off again? When you noticed it, was it via a scanner or the gauge?

Let me know.

Joe
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Tuesday, May 10th, 2022 AT 7:01 PM
Tiny
JOE BARTOLETTI
  • MEMBER
  • 8 POSTS
Got car 2 years ago. Thermostat was stuck open.
Scan tool said 155f after driving. Got a new thermostat.
1 month ago after flush it went into 205 range. 215 fans come on.
Went to the store yesterday. 190f as I got home.
Dash gauge is a touch low indicated now. Just a touch.
I need to drive it more. Sits too much.
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Sunday, May 29th, 2022 AT 6:07 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,755 POSTS
Hi,

The temperatures you indicated are good. Continue driving it and see if things change. It sounds like things are okay. Regardless, I'm here. Let me know if you need help with anything.

Take care,

Joe
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Sunday, May 29th, 2022 AT 7:31 PM

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