Engine Cooling Cycle - 2001 Chevy Venture
I was recently
concerned about the Cooling Cycle of my van because the temperature gauge
went all the way to the bottom of the scale while driving. At the same
time, the heater output seemed to be pretty cool, compared to what I was
used to, so I did NOT suspect a loose connection to the temperature sensor.
So I did a bit of "Data Gathering" on the cooling cycle of the van. I
use a diagnostic tool that allows me to log the data from various sensors in
the van over time. What you see below is a graph of the data while the
van was in my driveway.
Click for a Description
of the Engine Cooling System.
My plan was to run the van through two (2) cooling cycles. That
is, to the point where the cooling fans would turn ON, cool the engine
coolant, and then turn OFF again.
The numbers along the left side of the graph is the Engine Coolant
The numbers along the right side is the Engine Revolution Per Minute
The numbers at the bottom are just sample points as time goes by,
every few seconds (I didn't record the exact time).
The PINK line shows the ECT, the RED line shows the RPM, and the BLUE
shows the Throttle Position.
What The Graph Shows:
You can see what I did to get the engine coolant temperature to go up
in a relatively short time. I pressed on the throttle a few
times and you can see that by the Throttle Position points and the RPM
The first point of interest is when the temperature peaks at
about 226 degrees. At that point, the cooling fans turned
ON (I was watching) at their "LOW" setting (both fans in series with
12 volts, or about 6 volts to each fan). You can notice that the
system cools off pretty fast.
The second interesting point is when the fans turned OFF - this
was at about 200 degrees. You can see the temperature
drop to just below 200 (196 actually) and then start back up.
The third point of interest is where I turned ON the
defroster for the heater (heater fan on low). This caused
the RPM to jump to about 800, the AC compressor to turn ON, and the
fans turned ON. But what is interesting is that the
temperature continues to drop to about 176 after that. I
believe it should stay at about 195 degrees because the thermostat is
rated at that temperature (when it opens).
You can see where I turned the defroster OFF, and the temperature
starts to rise again and takes a while to get back to where the fans
turn ON again. The second time the defroster was turned on, I
left it ON for a longer time, and the reading from the sensor went all
the way down to 172 degrees.
My plan is to verify that these temperature reading are correct, using
another thermometer, and then have the thermostat replaced with a new
one. This needs to be done because all of these readings came
from the sensors installed in the van.
Note: I have VERIFIED the readings with an Infrared
Thermometer and the numbers are good, +- a few degrees.
I have already bought a new thermostat that is rated at 195 degrees,
and will have it installed as soon as I can. I haven't done it
yet because these vans can be tough to work on when it involves the
engine compartment. I even had my son try to replace the
thermostat (he is in an Automotive Training School), but too many
other parts need to come off before you can get to it and they have
limited time in the shop each day (2 hrs).
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