OHC Temp sensor accuracy - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 10-19-2009
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OHC Temp sensor accuracy

Anyone elses temp sensor off by 10 degrees or more? My scanguage will show intake temp, say at 60 and my OHC will show 65 I know AIT is probably 5-10 degrees hotter than ambient, so that puts my OHC 10-15 hotter than actual temps. I changed the position of the sensor, switched sensor and still get hotter temps. I might re-wire it to see if its the wiring causing a difference in resistance readings. I just wanna know if anyone else had noticed that.
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Old 10-19-2009
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did you look up the wire to the gem?
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Old 10-19-2009
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I have an 05, so no GEM for me, but I did hook up the VSS wire. Temp doesnt move when idling.
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Old 10-19-2009
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why do you think the intake temp would be the same as the out side temp?
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Old 10-19-2009
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air intake temp will be close to ambient, since air is outside in the ambient it will be VERY close to outside temp. I had my scanguage on my wife's camry. air intake temp would be 5-7 degrees hotter than outside temp displayed by her car. So in my case.....AIT, is a bit hotter than ambient (Normal), OHC is hotter than AIT (Not normal)...that doesnt make sense. OHC should atleast equal AIT...it should be lower actually, but Id be happy if AIT = OHC
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Old 10-19-2009
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air intake temps should be lower than the outs side temps because the ohc is programmed not to read the change of air because of the speed. the scan gauge is designed to read w.e the temp is and doesn't take the change in temp from driving or anything like that. i hope that makes scene
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Old 10-19-2009
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So youre saying the air intake temp, which is under the hood, where its hotter than ambient should be lower than ambient temperatures? That doesnt make sense. The temp sensor for the OHC is not under the hood, its outside where its cooler. The AIT sensor is right by the MAFS, where it gets HOT from engine heat. So why would AIT be lower than ambient?
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Old 10-19-2009
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Quote:
Originally Posted by eddiefromcali View Post
So youre saying the air intake temp, which is under the hood, where its hotter than ambient should be lower than ambient temperatures? That doesnt make sense. The temp sensor for the OHC is not under the hood, its outside where its cooler. The AIT sensor is right by the MAFS, where it gets HOT from engine heat. So why would AIT be lower than ambient?
The original post made absolutely no sense. I erased it because if you would have read it you would have in fact became dumber.

Last edited by RangerNDog; 10-19-2009 at 01:54 PM. Reason: Because today I am freaking retarted.
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Old 10-19-2009
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^^^ thats what i was trying to say
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Old 10-19-2009
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Originally Posted by RangerNDog View Post
I am going to assume that you have the stock intake. If you look at where it actually draws in the air it, it is from the outside right behind/beside the headlight. The reason the air is cooler is because the truck is moving and "making" a wind chill. The AIT sensor isn't programmed to compensate for the moving air so it read what the air is thus being cooler than the ambient temperature. The air may warm a lil but the short amount of time the air is in the intake tube before it reaches the AIT it should not warm much. The AIT should read as cool or cooler than the OHC except when you are moving at low speeds or idling.
Then I guess Im confused as to when the OHC stops the temp from moving. I thought that the VSS would not let the temp climb at idle and would let the temps change at any speeds above 0mph. Ive been driving through COLD weather @ hwy speeds and OHC reads something like 70F so I thought my sensor was bad. But what youre saying is that the temp wont change at idle and hwy speeds? hmmm....my Silverado would change temps at hwy speeds and the temp was in the mirror....I might be able to rig one up for a lil test and see how accurate the OHC is.
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Old 10-19-2009
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Mine reads smack dab on.

Reads same temp as:
The thermometer on the wall of my building.
My g/f's Corolla temp display
The chick who announces the weather on the radio
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Old 10-19-2009
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the IAT will never be colder than the outside air...period. there is no pressure loss for the air to lose heat from when it enters the air filter
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Old 10-19-2009
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I have the same problem as the OP. Does anyone know off hand what gauge wire the stock harness for the OAT temp sensor is? I have often suspected that improper resistance may be the culprit. Though in my case I don't have the speed sensor wire hooked up; I suppose I should do that before I rewire the whole thing.
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Old 10-19-2009
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Quote:
Originally Posted by eddiefromcali View Post
Then I guess Im confused as to when the OHC stops the temp from moving. I thought that the VSS would not let the temp climb at idle and would let the temps change at any speeds above 0mph. Ive been driving through COLD weather @ hwy speeds and OHC reads something like 70F so I thought my sensor was bad. But what youre saying is that the temp wont change at idle and hwy speeds? hmmm....my Silverado would change temps at hwy speeds and the temp was in the mirror....I might be able to rig one up for a lil test and see how accurate the OHC is.
The temp shouldn't move while your idling. It should move after the vehicle starts moving. This is so the OHC dosen't allow the sensor to display a false reading caused by the engine heat. Now why it shows 70F when the outside is cooler I can't tell ya, but I would try a new sensor.
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Old 10-19-2009
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Quote:
Originally Posted by Toreador4x4 View Post
the IAT will never be colder than the outside air...period. there is no pressure loss for the air to lose heat from when it enters the air filter
Your right. I don't know where my head it at today.
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