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.

Engine Cooling Cycle Plot

The Plan:
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. 

Data Points:
The numbers along the left side of the graph is the Engine Coolant Temperature (ECT).
The numbers along the right side is the Engine Revolution Per Minute (RPM).
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 line. 

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. 

Next Step:
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).

Van Home | Maintenance Index | Other Information