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Author Topic:   Temperature Gauge Calibration Adjustment
twrl posted 09-13-2009 03:51 PM ET (US)   Profile for twrl   Send Email to twrl  
Is there any way to adjust an OMC temperature gauge by changing a resister or something for a lower reading? Mine reads hot most of the time but the motor alarm doesn`t sound so I know [the motor] isn`t hot.
jimh posted 09-13-2009 05:42 PM ET (US)     Profile for jimh  Send Email to jimh     
An electrical remote temperature gauge is calibrated for use with a particular sender unit. If there is an error in the calibration, perhaps the sender and gauge are not match for each other.

You could experiment with adding a series resistance or a parallel resistance to affect the gauge calibration, but I have never heard of this being done. Generally the gauge and sender are well calibrated for each other.

twrl posted 09-14-2009 04:13 PM ET (US)     Profile for twrl  Send Email to twrl     
Thanks Jimh- One more question. Why does temp gauge show hotter with the engine running when I turn on the lights. Is there a wiring mix-up somewhere?
an86carrera posted 09-14-2009 05:01 PM ET (US)     Profile for an86carrera  Send Email to an86carrera     
There is probably a poor connection in your system. Or a VERY weak battery.


an86carrera posted 09-14-2009 06:47 PM ET (US)     Profile for an86carrera  Send Email to an86carrera     
Weak battery is probably wrong, sorry.


jimh posted 09-14-2009 08:01 PM ET (US)     Profile for jimh  Send Email to jimh     
An electrical temperature remote gauge works on this principle:

[Source of electrical current]-->[device to measure current]-->[device to control current proportional to temperature]

In the typical outboard motor electrical temperature remote gauge, the elements of the circuit are:

[Source of electrical current] = the boat battery

[device to measure current] = a milliameter meter calibrated in temperature

[device to control current proportional to temperature] = temperature sender

If you observe that the temperature indicated on your gauge changes when you turn on other loads in the vessel, the most reasonable explanation is that there has been a variation in the source of electrical current, the boat battery.

It might also be possible that you have a grotesque wiring error in the gauge illumination circuit and are adding the gauge illumination circuit current to the temperature sensor current, creating a totally false reading. This might happen if you have failed to observe the proper wiring for the gauge so that the current flowing on the gauge indicator is only the current flowing through the temperature sensor. Such grotesque errors in wiring are not particularly uncommon since boats are often wired by people who lack any understanding or appreciation of electrical principles.

number9 posted 09-14-2009 09:24 PM ET (US)     Profile for number9  Send Email to number9     
How much hotter when turning the lights on? If small it may just be a slight voltage drop to the gauge.

If you have a multimeter available you can check the resistance of the temp sensor. Not sure of your particular specs but should decrease as temp rises. If zero prior to warming up it's probably a bad sensor. Below is a link to typical gauge/sensor wiring with some troubleshooting suggestions that may be of some help.,WT,OT.pdf

twrl posted 09-15-2009 06:58 AM ET (US)     Profile for twrl  Send Email to twrl     
Thanks to all of you for the good information.I will examine the wiring.
White Bear posted 09-15-2009 08:09 AM ET (US)     Profile for White Bear  Send Email to White Bear     
If your temperature gauge reading is increasing when you add a load to the electrical system (such as lights), most likely your grounds are at fault. I would check the grounding connections in the user (light) circuit for corrosion and looseness before going elsewhere.
Stevebaz posted 09-15-2009 04:37 PM ET (US)     Profile for Stevebaz  Send Email to Stevebaz     
More than likely the rise in your temperature reading when your lights are on is because of the increased load on the electrical system. Since your gauge system is more than likely run from the unregulated battery voltage when you turn on your lights your charging system sees a voltage drop and kicks in the charging regulator increasing the battery voltage. Your gauge system is not voltage regulated so the increases raises the Temperature reading.
Jerry Townsend posted 09-15-2009 06:02 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Your temperature sensor is probably one or more thermocouples embodied in a potentiometer type circuit - and there will be a calibrating pot(entiometer) (a small, finely adjustable resistor). This adjustment will be "buried" and may not be accessible. Regarding adding a resistance - you don't know which way to go - adding resistance - or removing resistance and then to add resistence in series or in parallel. Regardless, guessing which way to go and by how much can lead down a very, very long road.

Therefore, you may be further ahead just getting another guage.

Regarding your question on different readings when your lights are turned on - a bit questionable - but it sounds to me like your regulator is doing a sloppy job - or not regulating within a close band. Another thought just came to mind - check your meter and make sure the power contacts are connected to the battery - as the battery is a very good regulator in itself. But - put a meter on your battery and see what it reads with the engine running and the lights on and off. ---- Jerry/Idaho

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