Am I Overheating? Temp Gauges Don't Agree.

[Scott & Heather]

My engine bay temp gauge reads thus when warmed up:

Simultaneously wife can take a pic of my dash gauge and it reads thus:


How can I remedy this?


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[luvrbus]

You use resistance coils at the sender that is done by wrapping the wire around a pencil making a coil it probably had those but have been straighten out over the years 

good luck

[sparkplug188]

Uh ohh    I am in the process of completely rewiring my bus and have removed all of the coils you speak of.  I figured they were some sort of strain relief.  Would it be possible to substitute a potentiometer in place of the coiled wire?  If so, about how many ohms of resistance does the coiled wire create?

Edit: Like one of these:
Wirewound Variable Resistor 50W Watts 20 Ohm Ceramic Rheostat

[TomC]

I would just replace the dash gauge. The full sweep gauge, like in the engine compartment is so much more accurate and easier to read. Good Luck, TomC

[lostagain]

What temp does the engine gauge read? I can't tell from the picture.


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[RickB]

Scott, If one sender is on one side of the block and the other is on the other side, you could have a thermostat hanging up on the hot side. Ir gun pointed at non shiny places on the block should be able to tell you which one is accurate or if you have a problem on one side of the engine. I always check both thermostats and I check before the thermostat and after it on the housing.

Just a thought

Rick

[Scott & Heather]

Excellent.
1. I have not seen said coils anywhere. Could be an issue
2. Temp gauge in engine compartment reads just a hair above 175
3. I'll try the HR gun. How accurate is it in your opinion?


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[sparkplug188]

This is one of the coils I pulled out of my pile of wire to recycle.

0.3 ohms when coiled



0.0 ohms when straightened



This is my attempt to recreate the coil using new wire

0.1 ohms when coiled



0.0 ohms when straightened



Coiling the wire does increase resistance a VERY small amount.  I believe you could set this 12 ohm 100 watt tubular variable resistor to half an ohm to get the same results as coiling the wire...  maybe.  I am hoping someone else shares my dislike of coiled wire and has come up with a solution.  

[HB of CJ]

Take a laser temp taking thingie and measure the hot side water hoses closest to the water pump.  Make sure the laser gage thingie is accurate using the roiling boiling water test. (compensating for altitude)

Then you know what gage is not reading what.  FWIW, usually, but not always, a gage dedicated right next to or actually on the mill may read more accurately, all things considered.

Also then consider finding and using a gage set that you like, can read quickly and if possible, have all the needles or dials centered in just one common position, be what that may be.

All the old mechanical Stewart Warner gages on my as old Crown Supercoach were matched in style and had the rare trait of being exactly centered in the high noon 12 o'clock position.

Not counting the speedo and tack, which seemed to vary when shifting up or down or coasting or something like that.  The tack seemed to work harder than the speedo. shifting up.

Except the gas gage, which for some reason changed rather quickly when the old girl was driven some distance.  Had something to do with fuel consumption or kinda like that.  HB of CJ (old coot)

[sparkplug188]

A retired electrical engineer friend of mine verified both resistance coils and variable resistors can be used to calibrate temperature gauges.  However, she had her doubts about 6 coils of 14 gauge having any significant influence on the temperature gauge.  At ambient temperature, my temperature sender has a resistance value of 648 k ohms.  Adding half an ohm to the circuit just doesn't seem like it will change much.  She said, once you find find a stable temperature with your IR gun, you will likely need to add anywhere from 100 ohms to 1k ohms to change the temperature on your gauge a few degrees.  Some temperature gauges have a calibration adjustment screw-- however, mine does not.

That being said, neither of us have any significant experience with bus electrical systems.

[luvrbus]

I don't know about MCI gauges I just watched the guys at Eagle in Brownsville and they would spend hours on the final inspection using the coils to set the VDO gauges right on the money same with the Cadillac shut down system they always had a battery charger on the batteries when setting those for some reason

[sparkplug188]

It is possible the resistance value increases quite a lot once significant current passes through the coil.  I am inclined to believe Cliffords first hand observation and experience.  The battery charger was probably used to simulate the alternator charging voltage when driving down the road. If the gauges were calibrated with the batteries at rest, say 12.8 volts, the gauges would read a few degrees higher than when being charged by the alternator, about 14.3 volts.

[gus]

I use my IR thermometer directly at the temp sensor and compensate accordingly, mine reads 13 degrees too low at the panel.

As long as I know this diff I don't care what the gage says:)

[Tikvah]

What about a digital gauge?  Maybe two (each side of the engine). Do we need all the twisty wire stuff for that?  Would it be more accurate at the dash?

Just run a wire, plug it in.  Am I wrong? 

Thinking of doing this myself.

Dave

[sparkplug188]

The reason our analog gauges need to be calibrated is because the gauge manufacturer never knows how long the wire will be between the temperature sending unit and the gauge.  Many digital gauges work the same way, electrically speaking, as our analog gauges and also need to be calibrated.  To avoid doing any sort of calibration, you will need to find a digital temperature sending unit and matching digital gauge.   The temperature gets sent to the gauge as a numerical value which isn't affected by distance between the sending unit and gauge.  I don't know for sure, but that sounds like big $$$ to me.

If it were me, I would first try coiling the wire around a pencil a few times.  It costs $0 and will probably fix the problem.  If it doesn't fix the problem, try an inexpensive gauge that has a calibration screw.  You will be able to dial the temperature in with a pocket screw driver.