TEST 2: Fan Operation
If you have already confirmed that the thermostat is indeed working fine, and yet your car or mini-van is still overheating, this section might help.
Since you still have your scan tool connected (to the vehicle), you can check to see if the radiator fan (or fans) are turning On at the right coolant temperature.
The testing steps I'm introducing here are pretty much a continuation of the previous test.
Alright, this is what you'll need to do:
With your scan tool still connected from the previous test (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
Let your 3.1L or 3.4L car or mini-van's engine continue running while you keep your eyes on the coolant temperature sensor's reading on your scan tool.
When the coolant temperature sensor shows you that it has reached 225° F (107° C), you should see the fan or fans start to turn on.
The maximum temperature that the engine should reach is 227° F (108° C).
At this temperature, the fan (or fans) should be turning at full blast and you should see the temperature decreasing on your scan tool's display.
If the fans do not come on at 227° F, immediately turn off the engine.
This let's you know that you have a radiator fan issue. Read the interpretations below for some testing suggestions.
If the fan (or fans) did come on, then you should see the temp sensor's reading decreasing to about 200° F (93° C). At this temperature point, the fan (or fans) should turn off and the cycle will repeat.
If this did not happen, read the test interpretations below for further testing tips.
Let's interpret the result of your test:
CASE 1: The fan (or fans) did NOT come on at 225° F - 227° F. This confirms that the overheating problem is due to malfunctioning fan motors.
Possible malfunctioning components could be: a bad fan motor, a bad fan motor relay, or/and a blown fan motor Fuse. Although, testing these components is beyond the scope of this article, you now at least have a solid lead on what's causing your vehicle to overheat.
CASE 2: The fan (or fans) did come on at 225° F - 227° F, but the vehicle continues to overheat. If you have also confirmed that the thermostat is good, then the most likely cause of the overheating issue is a blown head gasket.
You can find three specific tests, to verify a blown head gasket in this article: How To Do A Blown Head Gasket Test (GM 3.1L, 3.4L).
CASE 3: The fan (or fans) did come on at 225° F - 227° F and the temperature DID go down. This confirms that the fans and thermostat are OK. No further testing is needed.
Engine Thermostat Basics
In case you're wondering why the engine has one and needs one, well this section might shed some light on the subject (don't worry, I won't go into minute technical mumbo jumbo).
In a nutshell, the thermostat's job is to help regulate the engine's temperature. The PCM needs to have the engine within a certain temperature range to effectively control the emissions that the engine produces and to help you get the maximum amount of gas mileage possible. This temperature range is between 190° to 225° Fahrenheit (87° to 107° Celsius).
Continued on the next page...