MACS Monthly Newsletter - 2020 - APR2

Mahle
Gates

Figure 4: Mapped thermostats have internal electric heaters
controlled by the ECM's software "map" to move the stat's
position quickly for more precise engine thermal management.
Both conventional and mapped designs shown are of the bypass design. The lower valve can be open or closed allowing
the coolant to flow through the bypass passage during closed
(cold engine) or partially open positions. Regardless of bypass or
non-bypass design differences, both conventional and mapped
electrically heated thermostats have the same mechanical components such as a flange, spring and wax pellet.

Mahle

Figure 2: This thermostat (#33973) is not a bypass design but may
be a similar size to that in Figure 1. Both stats could 'fit' in the thermostat housing and have the correct temperature for the vehicle.
Could the wrong stat with the correct temperature cause an overheating condition? Maybe not, but you'd be wise to replace with
the correct stat if a stubborn P0128 performance DTC or heater
performance is your customer's problem!

Gates

Figure 3: A conventional bypass thermostat design.
Partly due to experience with P0128 DTCs and considering his temperature over time observations,
Mike was leaning towards a thermostat being stubborn to open within the right temp range on time.
Responses to Mike's post were plentiful and helpful, coming from a wide range of very sharp technicians. The first post came in from a shop owner who
suggested replacing the OEM stat (he had installed
two of them so far) with an aftermarket brand thermostat. Some other techs echoed that same idea.
In addition to the temperature specification of the
thermostat, there are a large variety of thermostat
designs. See Figures 1 through 5. A few techs went
the extra mile to post suggestions on exactly how to
check a thermostat on and off the vehicle.

April 2020

Figure 5: Thermostat specs . . . More than just temperature! This page from Gates' online catalog has an abundance of information on each of their stats. Type, presence
of jiggle pin, flange diameter, height from flange, design
and of course the opening temperature. The designs shown
in the drop-down menu illustrate the abundance of variations out there. Get the correct thermostat. Just because it
fits doesn't mean it will work correctly!

2

MACS Service Reports

MACS Monthly Newsletter - 2020

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2020

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