bad temp sensor or what?
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Member
Joined: Feb 2006
Posts: 20
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From: bryan, tx
bad temp sensor or what?
5.4l 1997 f150
temp sender is in intake manifold crossover (second one measuring head temp too)
my dash gauge has quit reading after an overhaul where I changed out the senders. It is always at cold (no movement). If I disconnect it no movement, if I jumper the electrical connector contacts it reads hot. this happened with an overhaul when I replaced the sender unit. I've since bought a second sender unit and its doing the same thing. Am I buying the wrong one? I have WT3058P from advancedautoparts.com. I see they also sell one without the "P" that also says exact fit.
Another question - the computer uses the head temp, correct, so I don't have to worry about this messing up the mixture?
temp sender is in intake manifold crossover (second one measuring head temp too)
my dash gauge has quit reading after an overhaul where I changed out the senders. It is always at cold (no movement). If I disconnect it no movement, if I jumper the electrical connector contacts it reads hot. this happened with an overhaul when I replaced the sender unit. I've since bought a second sender unit and its doing the same thing. Am I buying the wrong one? I have WT3058P from advancedautoparts.com. I see they also sell one without the "P" that also says exact fit.
Another question - the computer uses the head temp, correct, so I don't have to worry about this messing up the mixture?
Senior Member
Joined: Jul 2004
Posts: 6,200
Likes: 39
From: Easton, Pa.
Let me get this right; if you ground the lead at the sensor location and the dash gauge goes full scale?
If yes, the sensor is not grounded. Did you use Teflon tape of some type as a sealer on the threads? If yes you lost the sensor ground.
Test this by hooking up a sensor and grounding the housing to the motor or testing the sensor on the motor resistance with a meter.
Here are some resistance check points.
At about 104 degrees the resistance should be about 16,000 ohms.
At about 86 degrees the resistance should be in the 24,000 ohm range.
At 68 should be about 37,500.
50 degrees about 60,000 ohms.
As the temps goes down the resistance gets higher.
The early trucks used both a head sensor and a coolant sensor.
Later they were combined in function because both were looking at the coolant temp.
One plays a big part in cold starts and motor protection from overheating.
Good luck.
If yes, the sensor is not grounded. Did you use Teflon tape of some type as a sealer on the threads? If yes you lost the sensor ground.
Test this by hooking up a sensor and grounding the housing to the motor or testing the sensor on the motor resistance with a meter.
Here are some resistance check points.
At about 104 degrees the resistance should be about 16,000 ohms.
At about 86 degrees the resistance should be in the 24,000 ohm range.
At 68 should be about 37,500.
50 degrees about 60,000 ohms.
As the temps goes down the resistance gets higher.
The early trucks used both a head sensor and a coolant sensor.
Later they were combined in function because both were looking at the coolant temp.
One plays a big part in cold starts and motor protection from overheating.
Good luck.
Technical Article Contributor
Joined: Oct 2005
Posts: 25,641
Likes: 19
From: MI
There has been two types over the years. One of those like to trap air just under. If you crack the sensor loose while she's flowing, it will purge it. Kind of like cracking injectors on a old diesel, if they have ran out of fuel.
