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Dodge Repair/Temperature gauge reads high: '98 Neon

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QUESTION: Hi,

my 98 neon 146k miles temperature guage just started going high even when the engine isn't hot.  The fan kicks on late around 3/4 to the hot position even when I just turn the key on.  But when ther fan finally kicks on when the engine is running the temp guage goes back to normal.  Once the fan goes off it may or may not kick on.  This happened after we changed ther alternator and powerster belt...not sure if it is related but this never happened til then.

Thanks for your help.

ANSWER: Hi Hyer,
There may be a fault in the coolant temp sensor which is found on the rear surface of the cylinder head near the camshaft position sensor, at that same location. It has a 2-wire connector with colors black/light blue and tan/black. Check the condition of the wire harness as far as practical for any signs of damage to the insulation. Then read the resistance across the pins of the sensor when the engine is cold, as it warms up, and when you believe it to be at the operating temperature. It should usually read 3-4,000 ohms when cold and decrease gradually as the engine warms and reach about 1,000 ohms at operating temperature (but I don't have the specifics for this exact sensor so let me know if otherwise). I doubt this problem has anything to do with the belt exchange at the front of the engine. The fan control and gauge are both based upon the accuracy of the coolant temp sensor so that is the first item to check out.
At this many miles/age the problem may be related to the radiator not allowing coolant to flow freely so check for that possibility as an alternative explanation of the problem.
Sorry for the delay in answering your question but I just found it in the 'pool' to which it had been referred by Kevin.
Please 'rate/nominate' my answer/me (see the PS below).
Thanks,
Roland


---------- FOLLOW-UP ----------

QUESTION: I forgot to mention We have already change the coolant temp sensor and checked the wires.  Someone said these Neons has a temp guage sensor as well with only one wire that  control the temp guage but we have no idea where it's located or could be the problem.  Also someone said the fan relay may be the problem.I read there has been an epidemic of fan relay's going out all the time on theses but there isn't a recall.  I would appreciated it if you could let me know if either of these sound like something that makes sense to you.  

Thank you for your help!

Answer
Hi Hyer,
Here is what I know about the sensor based upon the '97 and '02 manuals that I have.
In the '97 model year the sensor has three wires: one directly for the gauge, one for the pcm signal and one for the pcm signal ground. In the '02 there are only 2 wires: one for the pcm signal and one to the pcm ground (and the pcm informs the bcm which in turn informs the cluster gauge). If you have changed it out then it is one or the other and is presumably working accurately.
As to the fan control: in the '97 manual there is shown a fan control pulse width module which is solid state. It is mounted on the left front inner frame just below the radiator. It has a 4-wire plug. These solid state relays were a reliability problem in the minivans of that time period so this may be why the fan is functioning irrationally as you described. If you replace it be sure to bolt it firmly to the frame as it needs to have a heat sink so as not to overheat. In the '02 the conventional fan relay is in the very front of the power distribution center under the hood.
I suspect your '98 has what is shown in the '97 manual and that might well explain the fan malfunction. As to the gauge reading you could check the continuity of the violet/yellow wire from the sensor pin C that goes through 2 disconnects before it reaches the cluster on pin 4 of one or the other of the black plugs at the cluster (which one is not shown but look for the wire color on both plugs at pin 4.
I wish I had the '98 manual, but this is the best I can offer you.
Please 'rate/nominate' both of my answers if you believe I have been helpful to you.
Roland

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Roland Finston

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Get a Free Fast answer to your repair question about a Chrysler/Dodge/Plymouth car, minivan, SUV, or truck. Problems with electronically controlled engines and transmissions as well as body wiring problems are my specialty. This free troubleshoot advice forum helps you diagnose faults, minimize repair costs or do-it-yourself.

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Five decades as a 'do-it-yourselfer' on domestic and imported cars

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Yahoo Autos Group called The Chrysler Lebaron Club (co-moderator)

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Degrees in Physics/bruised knuckles.

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"Top expert" of 2010, 2011, 2012, 2013, 2014, and 2015 here at Allexperts. Quickest "average response time" at Allexperts (currently no. 1).

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