ACtion Magazine - April 2017 - 14

Slow to heat

By Steve Schaeber, MACS Technical Editor
echnicians who've dealt with engine overheating problems know
that when the cooling system isn't working as it should, temperatures can climb real high, real quick. In fact, some faults such as
a stuck closed thermostat, broken drive belt, inop water pump, clogged
radiator or even low coolant level can cause a cold temperature gauge to
spike within minutes, even under no load and at idle. This is due to the
enormous amount of heat generated during combustion, and it's the cooling system's job to keep things under control.
But things are changing in the world of engine design, and these
changes are bringing a new set of owner experiences. Causes may be different from what we're used to seeing in the shop. If a customer were to
say their heater isn't getting hot enough, or that their engine takes a long
time to warm up, your first thought might be a stuck open thermostat. But
before you dive into this once-in-a-while repair, keep this report in mind.
Thanks in part to more strict emission regulations and improved fuel
economy targets (54.5 mpg by the 2025 model year), many of today's
modern engine designs are pushing efficiency to the extreme. Engineers
are doing everything they can to eliminate waste, even in the smallest
amounts, in an effort to reduce mass and use less fuel, and that includes
targeting waste heat from combustion. They're not lowering operating
temperature as such, since engines will still need to burn hot enough to
keep tailpipe emissions low, but they are getting to the point where so little
excess heat is generated that liquid coolant temperatures outside of the
engine block are lower than we're used to.

ACTION * April 2017

GM recently made note of these concerns in their Preliminary Information Bulletin #PI1166D: "Vehicle Slow to Heat Up in Cold Ambient
Temperatures," issued on Jan 24, 2017. Affected vehicles are certain
2011-2017 models, including the Buick Encore and Chevrolet Cruze,
Sonic, Spark and Trax with 1.2L, 1.4L or 1.8L engines. These energy
efficient engines may not generate the same amount of heat at idle
that the customer is used to experiencing with older, less efficient
engines. Also, short drives under low load in colder ambient conditions may not create enough heat to increase coolant temperature
(and gauge readings), thereby producing lower air temperature at the
heater vents.
Technicians should first check for any trouble codes, and then
verify proper coolant level in the surge tank. If that checks out OK,
technicians should communicate with the customer, instructing them
to place the fan speed on medium (rather than high) during warm up
or when idling. This will produce warmer outlet temperatures. because the heater core won't cool off so quickly. Technicians should
not, however, replace the thermostat unless a specific DTC code has
set. The PCM monitors thermostat operation closely to ensure it's
operating properly.
If there are no DTCs, the coolant level is correct and the thermostat is operating properly, then "Slow to Heat" should be considered
a normal characteristic of these energy efficient engines. ❆

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Table of Contents for the Digital Edition of ACtion Magazine - April 2017