Continued from the previous page.
Connect your scan tool to the vehicle and get to its Live Data mode. Scroll down to the PID for the coolant temp sensor (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
Leave the hood open and start the engine. As the engine warms up, keep your eyes on the coolant temperature sensor's values on your scan tool.
If you started out with an engine at ambient temperature, then your scan tool should report a coolant temperature sensor temperature that should be within 10 degrees of ambient temperature. For example, If it's 95° F outside, then the coolant temperature sensor should report a temp reading between 95 to 105° F.
As the engine continues to warm up and the coolant temp sensor shows 150° Fahrenheit (65° C) on your scan tool, lightly touch the upper radiator hose to check its temperature.
The hose should still be cold (ambient temperature). In other words, it should be the same temperature as before you started the engine, if so, continue to step 6.
If the hose is hot, then this confirms that the thermostat is stuck open or missing. You can stop here, since there's no further need to go on to the next steps. Replace the thermostat.
When the coolant temp sensor shows 190° Fahrenheit (87° C), lightly touch the upper radiator hose once again.
You should feel a definite warming up of the upper radiator hose (compared to its temperature at the beginning of the test).
If the hose does not feel like it's heating up, don't worry about it just yet, continue to the next step.
Let the engine run till the scan tool reports a temperature of 200° F (93° C) and lightly touch the upper radiator hose again.
If the thermostat is functioning correctly, the hose will be hot.
Alright, you're done. Turn the engine off and let's interpret your test results.
CASE 1: The radiator hose got hot at 190° F and stayed hot at 200° F. This confirms that the thermostat is functioning correctly.
CASE 2: The radiator hose DID NOT get hot at 190° F nor at 200° F. This confirms that the thermostat is bad and is stuck closed. Replace the thermostat.
CASE 3: The radiator hose got hot below 150° F. This confirms that the thermostat is bad and is stuck open. Replace the thermostat.
Here's why: If the thermostat were working correctly, it would not let any coolant circulate within the hose and the hose would be at ambient temperature. Since the thermostat is stuck open (or missing) the coolant starts to circulate immediately and the hose will feel warm to hot as soon as the engine has been running for a few minutes.
TEST 2: Electric Fan Motor 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.
Before we start, let me tell you that this test is only applies to Ford 3.0L, 3.8L vehicles with an electric fan motor.
One more thing, the A.C. has to be turned off to successfully complete this test. Alright, this is what you'll need to do:
Restart the engine in your car or minivan and with your scan tool still connected (from the previous test) check the coolant temperature once again (Don't have a scan tool? Need a scan tool? Check out my recommendation: Actron CP9580 Scan Tool).
The temperature that you're waiting for is 225° F (107° C). This is the temperature at which the radiator fan motor should start.
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 your scan tool should be reporting a decreasing coolant temperature reading.
Once the temperature goes down to about 200° F, the fan motor should turn off.
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 and the coolant temperature does not come down (from 227° F) but continues to climb, turn off the engine and let it cool down.
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 your vehicle is experiencing is due to a fan motor issue.
The next step is to check the fan motor itself. Other components that can cause the fan motor not to operate are: 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 (in TEST 1), 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 tutorial: How To Test For A Blown Head Gasket (Ford 3.0L, 3.8L).
CASE 3: The fan (or fans) did come on at 225° F - 227° F but the temperature DID go down. This confirms that the fan(s) and thermostat are OK. No further testing is needed.