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Old 10-25-2008, 05:37 PM   #1
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Question Monitoring clutch fan

The full grille block test (well, radiator block) on my truck did not cause the temperature to budge, not even slightly. It's got a clutch fan instead of an electric fan. Is there a way I can monitor the fan to know when it's running?
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Old 10-25-2008, 06:08 PM   #2
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Mechanical fan? Not likely... unless you want to mount a hall effect sensor to it.

Don't trust OEM coolant temp gauges. By the time they tell you that you're overheating, you're already doing critical engine damage. For instance on my VX, the needle is in exactly the same position from 176 to 230 degrees! Yet above the temp when the rad fan comes on approx 205 F, the engine is suffering from accelerated wear. Heat kills engines.
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Old 10-25-2008, 06:41 PM   #3
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I didn't see problems with OEM temp guages, in 30 years of working on cars. Confirmed with touching the top hose with my hand and using a digital thermometer. Maybe your problems were with only Hondas, Hatch, or your individual vehicle.

I also demonstrated bad fan clutches by taking a shop rag and stopping the fan from the rear and spinning it backwards while the engione was running (no its not a misprint and it was a very effective demonstration, to confirm a bad clutch when the engine started overheating at idle).

Mercedes stated very clearly that their engines could operate without damage up to 256 degrees F, as long as the anitifreeze ratio was correct.

When a clutch fan "hooks up" you can easily tell the difference in the fan noise. If your grille block is to effective you could be loosing power driving the fan at greater speeds which will eat up some HP.

Probably better to switch to an electric fan.

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Old 10-25-2008, 06:51 PM   #4
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Mechanical fans and grille blocks aren't the best combo in my experience. The block makes the fan itself run a little hotter and starts trying to move more air regardless of whether it can or not.

When I did my block it only lasted a day because I'd take off from a light and could hear the fan pulling hard and feel the car gain power as the fan let go once I was moving again.

Now, a FLEX fan is a different story.
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Old 10-25-2008, 06:56 PM   #5
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Quote:
Originally Posted by R.I.D.E. View Post
Maybe your problems were with only Hondas, Hatch, or your individual vehicle.
That's my guess as to the reason behind the common complaint of OEM gauges being inaccurate. I haven't compiled the statistics, but I wouldn't be surprised if all the bad gauges were Honda and/or Toyota.

My truck's gauge is definitely accurate and fast-responding. I admit I haven't taken measurements, but after nearly 180,000 miles I'm very familiar with it. The only way to make it rise from its normal spot is dragging a 6000 pound camper straight up a mountain, such that I can't actually maintain the speed I want, when the temperature outside is 85 degrees or higher. Doing so makes it rise rather quickly, and letting the engine rest makes it fall just as fast.

My tachometer, a gauge also often suggested as being inaccurate, now that's something that I have confirmed with measurements. Tachometers on my GM vehicles and my VW are definitely accurate and real-time.

Quote:
When a clutch fan "hooks up" you can easily tell the difference in the fan noise. If your grille block is to effective you could be loosing power driving the fan at greater speeds which will eat up some HP.
This is exactly my fear. The setup I did today is just for testing to make sure it won't overheat, and when I do the actual grille block it's going to be more open. Today's work is between the transmission cooler and the A/C radiator, while the plan for the permanent grille block is in front of the grille (for aerodynamic effect as well as heat retention); it will have a decent sized hole for the tranny cooler, which will also let air in to cool the engine radiator.

Quote:
Probably better to switch to an electric fan.
This can be done pretty inexpensively using fans from a junkyard. Unfortunately, "pretty inexpensive" is far beyond my available budget. I'm stuck with the clutch fan for the forseeable future.
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Old 10-25-2008, 07:31 PM   #6
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I have seen people drive fan clutch cars with the drive belt broken and they did not overheat as long as they were moving at over 25 MPH. The airlfow made the fan spin and the water pump kept turning with no belt.

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Old 10-26-2008, 11:42 AM   #7
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I was thinking about this more. How exactly is the clutch triggered? It must be thermostatically controlled, I'd guess with a bi-metal coil. Could I put a thermometer probe near wherever that is and watch temperature in that spot? Then I would know when the conditions should cause the fan to engage.
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Old 10-26-2008, 12:55 PM   #8
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Wire wound bimetallic spring on the front of the clutch opens and closes a bypass valve depending on temp of air flowing over the spring.

Believe me you can hear the difference in the fan noise when the clutch is engaged.

Many people think the clutch fans are not as efficient as an electric one. That may or may not be true, because when the airflow is sufficient the air flow will acutally spin the fan itself and relieve the necessity for the engine to do the same.

They are generally limited to a max speed of about 2500 RPM.

Of course blocking the grille could remove the air flow volume and cause the clutch to engage the fan to a much greater extent and sap engine power.

Your best bet may be to not block the portion directly in front of the radiator.

When you first start the engine the fan will wind up and you can hear it. When the clutch disengages (cold engine) the noise will become much lower in a few seconds. If the clutch siezes the fan noise will be much greater due to the fan being directly driven by the engine at much higher than its normal speed.

Be very careful of a weak clutch (old and worn out). It will not engage enough to properly cool the engine. The normal symptoms of this are overheating when sitting still.

regards
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Old 10-26-2008, 01:25 PM   #9
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Quote:
Originally Posted by R.I.D.E. View Post
Believe me you can hear the difference in the fan noise when the clutch is engaged.
Alas, that's only true when the windows are open, the vehicle isn't moving, and accessories are off. Closing the windows and driving is enough to cover the sound. The OEM soundproofing is quite good.

Quote:
Your best bet may be to not block the portion directly in front of the radiator.
There is no other portion. I guess I'll just experiment with it and see if it helps -- if I get an improvement in FE, should I really care whether or not the fan is running?
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Old 10-26-2008, 02:00 PM   #10
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I don't know about that one THC. In my cars you can can always tell when the fan is working hard while you are accelerating. They can get loud.
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