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Coolant temp readings

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Old May 31, 2010 | 10:21 PM
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From: Eaton, CO
Coolant temp readings

My stock gauge looks to hang out around the H. I bought an infrared temp reader and shot the top and bottom of my radiator just after shutting it off when it got near the H.

Top: 195.8 degrees Fahrenheit
Bottom: 106 degrees Fahrenheit

I shot the solid metal areas only, so the very top and bottom.

That's a 90 degree difference. Did I shoot the wrong point at the bottom? What gives?
 
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Old May 31, 2010 | 10:36 PM
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From: Elk City, OK
it should be cooler at the bottom. as the water travels down the radiator it should cool, plus hot water rises so the cooler water will be lower in the radiator.
 
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Old May 31, 2010 | 10:46 PM
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From: Elk City, OK
you could always get a cooking thermometer. glass tube. or get a baking one, that is metal probe. fire up the truck with the radiator cap off, stick the thermometer in there and let it get warm. once it gets "to temp" then check the coolant temp reading on it. the water temp should be different from the metal, since the metal is being cooled from the passing air
 
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Old May 31, 2010 | 10:49 PM
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I put an aftermarket temp sensor from Schuck's in the truck and it "fixed" the gauge to actually make the needle register. That's when it would register on the H or near it after the motor warmed up. My motor takes the bullet style sensor and the guy at Schuck's said that was for an '87, not an '86. Bad sensor or gauge?

The hose that goes from the top of the radiator to the t-stat seems pretty hard when the motor is fully warmed up and soft when cool.
 
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Old May 31, 2010 | 11:00 PM
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ya, thats just the water that turns into vapor when the water gets warm. your water is near boiling when your engine is running, any place that there is oxygen is replaced with steam. your radiator cap should be 13lbs. thats how much pressure the cap will hold before it opens and lets excess vapor/water overflow into the overflow tank. all normal
 
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Old May 31, 2010 | 11:19 PM
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Well that's a relief... How do I check the fan clutch? I don't think I've ever heard it turn on.
 
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Old May 31, 2010 | 11:31 PM
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Im pretty new to mechanical fans, and correct me if i'm wrong, but the fan should for the most part always be engaged. The clutch disengages when you reach a higher cruising speed, because air is already being forced through the radiator. Not sure how to test it, maybe just rev the engine up and observe the fan.
 
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Old May 31, 2010 | 11:49 PM
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with the engine off, the fan will always free spin (with resistance that is) the way to test it is, take your truck for a drive. when the engine gets hot (normal driving temp) shut the truck off, hope out and pop the hood. spin the fan with your hand. if it will not turn or is a lot harder to turn then it works. the heat hitting the center coil section will lock up the fan where you can not turn it by hand. if it still spins as free as it did when the engine was cool then the clutch is bad
 
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Old Jun 1, 2010 | 05:15 AM
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My new mechanical gauge hits 200*F before the stock gauge moves.....

Also, the fan clutch is a fluid coupling. When the fluid heats up the resistance through the fan clutch increase thus increasing fan speed (cooling capability). Likewise, when the fluid temp. decreases the clutch will slip. As stated in a previous post, the fan should turn freely by hand (with some resistance...) when cold. I was taught that if you spin it by hand the resistance through the coupling should stop it from turning in less than 1 to 1 1/2 turns, if freewheel is excessive than the fan clutch is worn beyond limits.
 
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Old Jun 1, 2010 | 06:55 AM
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I'm going to give the fan clutch a test today.
 
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Old Jun 2, 2010 | 07:43 AM
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I didn't notice any difference in feel after a 15 minute drive and the gauge was on the line before H.
 
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Old Jun 2, 2010 | 08:24 AM
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My fan doesn't lock up until around 205 degrees, which it never see's unless it is pulling a good load usually in the mountains.
 
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