My engine bay temp gauge reads thus when warmed up:
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fimg.tapatalk.com%2Fd%2F14%2F06%2F02%2Fqa9aruby.jpg&hash=46d75368cd3a6bfd57a360408131daf5916fed1c)
Simultaneously wife can take a pic of my dash gauge and it reads thus:
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fimg.tapatalk.com%2Fd%2F14%2F06%2F02%2Fsy3egamy.jpg&hash=c4be8c47350598f69f3c017a157e1d37a1735aa2)
How can I remedy this?
Sent from my iPhone using Tapatalk. Clumsy fingers may contribute to mistakes.
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
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
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FKwOzQpk.jpg&hash=fa2484713d9ba7892f128cd6595394a983a3c283)
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
What temp does the engine gauge read? I can't tell from the picture.
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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
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?
Sent from my iPhone using Tapatalk. Clumsy fingers may contribute to mistakes.
This is one of the coils I pulled out of my pile of wire to recycle.
0.3 ohms when coiled
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FzyBLWmz.jpg&hash=aa440444708f3cf77a20189a2dcedb76d9fb8173)
0.0 ohms when straightened
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FlyUcDJ9.jpg&hash=215a5f07f3bdaa2cd4af4838220eced328a42d00)
This is my attempt to recreate the coil using new wire
0.1 ohms when coiled
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FAQXqJiZ.jpg&hash=9b3ecaa57618e071ab7fdfb08cff23e9416c7c4a)
0.0 ohms when straightened
(https://busconversionmagazine.com/forum/proxy.php?request=http%3A%2F%2Fi.imgur.com%2FAdwAJyQ.jpg&hash=735872bba4460152ab86412368773d15efb4e4f2)
Coiling the wire does increase resistance a VERY small amount. I believe you could set this 12 ohm 100 watt tubular variable resistor (http://www.amazon.com/Amico-Ceramic-Adjustable-Rheostat-Resistor/dp/B008P3ZDHE/ref=sr_1_2?ie=UTF8&qid=1401748181&sr=8-2&keywords=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. ;D
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) :)
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.
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
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.
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:)
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
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.
Quote from: TomC on June 02, 2014, 06:33:30 AM
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
I agree. However, I've not yet found a 2-1/16" full-sweep black-face and black-bezel analog electrical temperature gauge for an affordable amount. Even Summit Racing, which has as good a selection as anywhere, doesn't seem to have anything suitable. My plan was to buy a full-sweep gauge to replace the present short-sweep Teleflex gauge, and then to also have a mechanical gauge at the rear-start panel on the passenger-side bank where all the temperature sensors now are (is that bank the hotter one?). I'm guessing I could reuse the present gauge's wiring for the new sender and gauge - will that work?
Ideally I would like a dual gauge with a sender on each bank, but they're even harder to find in a style and size that matches my present gauges. Didn't someone here post a photo a few months ago of, I think, an aircraft dual gauge? Mind you, if it were mechanical it's not going to be much good 40 feet from the engine!
John
A little out of the box. Mechanical gauges mounted in a box in the engine bay with a video camera and monitor up front
Rick
Digital or analog is not the problem, wire length and old corroded connections is.
Mine is digital which replaced an analog.
Mechanical panel gages are out of the question and such long wire runs make electrical ones inaccurate.
Rick's idea is not that far fetched but my method is much simpler and works.
Well hell just do it with 3 lights on the dash from senders mounted back at the engine lot's of boats just have 3 lights no gauges cold, normal and hot yellow, green and red
If the gages aren't accurate neither will the lights be. The problem is long run wire resistance.
Lites don't care about resistance for that application all they need is tempature controlled 2 wire open and close sender I have a system in the RV that uses lights it works pretty darn for to me
Lights are a simple and reliable way of getting the job done. If any one needs a schematic for temperature lights, I will gladly draw one up. It is a pretty simple setup-- I am sure most people can figure it out without a schematic.
FWIW Coiling the sensor wire is a valid way to calibrate VDO gauges. I had a hard time believing it until I tried it out myself. Just add more coils to decrease the displayed temperature or remove coils to increase the temperature.
In the OP, his dash gauge is reading higher than actual temperature (that is assuming the engine mounted gauge is accurate). That can not be caused by loose or corroded wires. The problem is actually to little resistance on the signal wire. The way to fix the problem without changing out equipment is to increase resistance on the signal wire. That can be done by adding coils to create more resistance or by using a variable resistor. I have ordered a few different variable resistors to try calibrating my gauges. I will post my findings when they arrive in a week or two.
I stand corrected on the lights, makes sense!
Loose connections and corrosion will definitely increase resistance. This causes mine to read low.