Troubleshooting Begins

When I finally went over to Oscar's place to take a look at his van, I rechecked everything he had replaced. Specifically:

  1. I checked if the van indeed had a blown head gasket.
  2. Tested the thermostat to make sure it was opening up at the correct engine coolant temperature.
  3. I visually checked that the water pump was NOT leaking coolant from its weep hole.
  4. Made sure that there were NO coolant leaks from the radiator, or any hoses or engine gaskets.
  5. Finally I tested the fan clutch.

It reads like I spent the entire day testing stuff... but it only took me about 20 minutes to do everything (but test the fan clutch).

Now, what I'm gonna' do in the next couple of pages is analyze all of the tests I performed to some detail. This way, if you're presented with a similar problem, you'll know what can be tested and how to test it.

Quickly Checking For A Blown Head Gasket

The very first thing I did (which was also the easiest) was to check to see if Oscar's van had a blown head gasket.

I'm gonna' briefly describe what I did here, but if you want to see the step-by-step blown head gasket tests, you can find them here: Blown Head Gasket Test (this ‘How To Test’ article is at

In the majority of blown head gasket cases, there are two things to look for:

  1. Coolant mixing with the engine oil.
  2. Exhaust gases/combustion pressures trying to escape thru' the radiator.

I checked to see if coolant was mixing with engine oil simply by pulling out the engine oil's dipstick and checking the color of the engine oil sticking to the stick.

And the engine oil was it's normal dark and dirty color. But, I wasn't done yet, since I needed to check one more thing.

The next step was to see if compression and/or exhaust pressures/gases were causing coolant to shoot out violently out of the radiator with the radiator cap removed.

So, I removed the radiator cap, and from a safe distance, but within view of the radiator's neck... I asked Oscar to crank the engine for me.

The coolant did NOT shootout violently from the radiator. I now knew that his fears of a blown head gasket were unfounded.

Quickly Checking The Thermostat's Operation

Now that I had eliminated a blown head gasket, the next step was to check the operation of the thermostat (even though Oscar had already replaced it with a new one)... specifically that it was opening up and letting the hot engine coolant circulate into the radiator at around 190° F.

This is another very easy test and it's done with a scan tool with Live Data capability. The only other requirement is that you have to start out with a cold engine.

I'm gonna' briefly describe what I did here, but if you want to see the step-by-step thermostat test, you can find it here: Thermostat Test (although this test is for the 4.3L, 5.0L and 5.7L engines, the info still applies).

The next step was to check the thermostat. This is what I did:

  1. I connected my generic scan tool and went to its Live Data mode.
    1. I scrolled down to the PID that showed me the coolant's temperature.
    2. Once there, I made sure the coolant temperature showed that the engine was cold.
  2. Checked the temperature of the upper radiator hose and made sure that it was cold to the touch.
  3. I started the engine and let it warm up.
  4. As the engine started to heat up, I kept my eyes on the coolant temperature the scan tool was reporting.
    1. Every couple of minutes, I checked the temperature of the upper hose.
  5. When the scan tool reported 190° F... I checked the temperature of the upper radiator hose
    1. The hose was starting to feel hot.
      1. This was the result I was expecting to let me know that the thermostat was indeed opening up.
  6. Once the scan tool reported 195-200° F, the upper radiator hose was completely hot.
    1. This confirmed that the thermostat was indeed doing its job of letting the hot coolant circulate into the radiator.

Now, in case you're wondering... If the upper radiator hose had not gotten hot (at around 190° F), I then would have known that the thermostat was not opening up and therefore I could conclude that Oscar had installed the thermostat incorrectly or had installed a defective one.

Having eliminated the thermostat, I was off to the next test....