Checking The Fan Clutch

By this point, Oscar's van had been idling for about 30 to 45 minutes and the engine was now at normal operating temperature and this meant that the fan clutch was also hot and hopefully operating in its engaged mode... so the next step was to manually check to see if the fan blades were locking up or freely spinning.

You and I can check this by turning off the now warmed up engine and spinning the fan blades by hand. If the fan clutch is in its Engaged Mode, then the fan blades should not be able to complete one or two revolutions.

This is what I did:

  1. Before I turned off the engine, I checked the coolant's temperature one more time, with the scan tool, and it read around 200° F (which also indicated that the engine was not overheating yet).
  2. Since the engine was still running, I turned it off.
  3. I then grabbed the edge of one of the fan blades and manually spinned it.
  4. The fan blade DID NOT spin freely.

Since the fan blades did not spin freely... I now knew that the fan clutch was in its Engaged mode. I was starting to think that the fan clutch was OK... but I have seen this before... where the fan clutch blades do not spin freely yet the fan clutch is BAD.

Also, the van was not overheating. So, I took it on a road test. I hadn't even gone 5 blocks when the van started to overheat. Not only that, but when I came to a stop the engine idle would get very high (the PCM was commanding a high Idle since it saw that the engine was overheating and was trying to spin the fan clutch faster with a higher idle).

I had one more test to do... and this was to manually lock up the fan clutch and road test it again.

Manually Locking Up The Thermal Fan Clutch

How To Test The Fan Clutch Case Study

Manually locking up a fan clutch to see if it's truly fried or not is an old mechanic's technique, and this was what I did next.

Before I jump into how I did it on the van, let me say that this technique (of manually locking up the fan clutch) involves placing the end of the bimetallic coil in another position (on the fan clutch itself) so that the shaft it's attached to is turned counter-clockwise.

When the shaft is manually turned in this way, the fan clutch immediately goes into and stays in its Engaged Mode all of the time. The end result is that it starts to pull in more air across the radiator. On the majority of older vehicles, the fan clutch is designed in such a way to you're able to this very easily.

Let me explain this in more detail:

  1. If you have ever noticed, the end of the Bimetallic spring is placed inside a groove or set against a tab that protrudes from the fan clutch itself.
  2. The thermal fan clutch will then have another groove or tab that's placed opposite of the one that the end of the bimetallic coil is placed in (not all fan clutches have this setup, but most do).
  3. So then, to manually lock up the fan clutch, all you do is remove the end (of the bimetallic coil) from its groove or tab and place it on the groove or tab directly opposite of the one it's in (if the fan clutch is so equipped).
  4. You then start and road test the vehicle and see if this solves the overheating problem. If it does, then you now know that the fan clutch is BAD and needs to be replaced.

On Oscar's Express van, it wasn't possible to place the bimetallic coil in another position because the fan clutch simply did not have this option... but I was able to manually lock up the fan clutch anyway, using a method that's a bit unorthodox (but that works) and I'll explain it in detail in the next couple of paragraphs.

Manually Locking Up The Thermal Fan Clutch (Part II)

How To Test The Fan Clutch Case Study

As mentioned before, Oscar's fan clutch didn't give me the option of locking up the fan clutch by repositioning the bimetallic coil... but I was able to do it anyway by removing the bimetallic coil and using a piece of metal (in the shape and size of the end of the coil) in its place to lock the shaft in its counter-clockwise position with epoxy.

Now, this... I'll confess, is a pretty extreme way of testing the fan clutch and it may not be everyone's cup of tea. But, keep in mind that I had already verified several important things and these were:

  1. No coolant leaks from anywhere on the engine, radiator, or water pump.
  2. Thermostat was functioning correctly.
  3. No indications of a blown head gasket.

And so, I felt confident that this was the only way to check the true condition of the fan clutch... not only that, but Oscar had already spent quite a bit of money on parts that had not solved the problem and did not want to throw anymore money at the van unless he was sure that the part was gonna' solve the problem.


This is what I did:

  1. I removed part of the fan shroud (to have good access to the bimetallic coil).
  2. Removed the bimetallic coil.
  3. I then found a small piece of metal that was about the same thickness as the end of the bimetallic coil.
  4. I placed one end of this piece of metal into the groove on the shaft.
  5. Using this piece of metal as a lever, I then turned the shaft to its maximum counter-clockwise position and then expoxied it (to lock the shaft in place).
  6. After waiting the time the epoxy needed to set, I road tested the van.

And the overheating problem was solved! That's right, no matter how far I drove the van (on the highway or not)... Oscar's van did not overheat anymore.

All Oscar needed to do was to run down to the auto parts store and buy a new fan clutch.