It’s too damn efficient!

Some highlights from Service Bulletin PI1166:

Subject: Vehicle Slow to Heat Up in Cold Ambient Temperatures


Some customers may comment in cold ambient temperatures on the following:

– The engine is slow to reach normal coolant operating temperatures as indicated by the engine coolant temperature gauge.

– The air coming out of the heater outlet ducts is not warm enough for their personal preferences.


The high energy efficient engines that this vehicle is equipped with may not generate the same amount of heat at idle that the customer may be accustomed to when compared with older less efficient engines. Additionally depending on extreme cold ambient temperatures, a short drive cycle under light engine load may also not generate enough heat to reach normal engine coolant operating temperatures as indicated by the engine coolant temperature gauge and therefore insufficient heat from the heater outlet ducts.


Please communicate to the customer that this condition as described is a normal operating characteristic of their vehicle. It will not impact the designed performance or reliability of the vehicle. Please share this information with the customer, including a copy of this information.


I spent an hour in my car this morning in stop and go traffic with no heat. It was about 18*F here, so not record cold by any means, but still, it was a chilly drive. I love how GM spins it, though - “air is not warm enough for their preference”. That assumes the air is warm in the first place, mine was not. And I’ve checked my coolant level and have no DTCs. I wonder if something is wrong with my heater core or if 18*F is just too cold for the Cruze.

UPDATE: I drove it home from work in 31*F and it was FINE! PERFECTLY, 100%, FINE. F#$%&ing CRUZE!!!



This morning was another cold one, 19*F, and it was a chilly drive in to work, though not as bad as yesterday, and I think I know why. I don’t think anything is wrong with the car, it’s not a thermostat, or a blocked heater, or anything else. It’s my dog.

Illustration for article titled F#$%ing Cruze [UPDATE 2: HEATER BOOGALOO]

Before I explain why, understand that my commute is about 15 miles and goes something like this:

  • 1/2 mile in neighborhood at 25
  • 2 miles on parkway at 50
  • 1 mile on major road at 0 to 50
  • 9 miles on hilly 2 lane road at 0 to 45
  • 2.5 miles on highway at 0 to 65

When I say “0 to XX” I mean it’s dependent on traffic conditions. See, before we got Ozzy I’d leave around 0630 and encountered very little traffic, so on those roads I was pushing the higher end of the speed limit and keeping the car under load and warming it up. Now that I have to walk and feed him in the mornings, I end up leaving closer to 0715 and encounter significantly more traffic, which leads to much more stop and go, so the car just doesn’t warm up because it’s rarely under sustained load.


I also remembered that the Cruze has a feature called Deceleration Fuel Cut-Off (DFCO). When the car is coasting in gear, it turns off fuel flow to save gas. As soon as either the clutch or throttle is depressed, fuel starts to flow again. It’s a fuel saving, economy boosting feature, but there’s a problem in the winter time. With no fuel flow, and no combustion occurring, the engine is just pumping air. Lots of cold, cold air, that’s sucking all the heat out of the cylinders.

Like a good engineer, I did an experiment this morning on the hilly sections of my drive. I watched the coolant temperature while coasting down hill, sometimes in gear (in DFCO condition) and sometimes with the clutch in or car in neutral (engine idling). I could watch the temperature drop rapidly in DFCO condition, but when I idled it the temperature would maintain.

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