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Old 09-29-2020, 09:13 PM   #1
Bus Crazy
 
Join Date: May 2016
Location: Georgia
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Year: 2001
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Coolant temp gauge calibration - help requested.

The story so far, I've had this bus around 4 years now. It's always run (shown) in the 180 degree range. Fan kicks in around 190-ish. And I checked, the coolant is full (enough).

The instrument cluster has been flaky for a couple years now. Dorman makes a replacement circuit board for it, which I bought (having reflowed the solder joints a couple years ago and the problem returned). The replacement went more-or-less smoothly enough, I have some LED dash lights that don't light up (they are polarity sensitive and I swapped them in the same orientation as previous, so anyone doing this, be sure to test LED bulbs prior to reinstallation!)

I also have a Nexiq-Clone and the ServiceMaxx software on my laptop. The ECM has been reprogrammed for the new gear ratio, along with enabling the cruise control, resetting the Road Speed Limiter to 80 (beyond the RPM and gearing capacity), and double checking the over-temp de-rate and alarm settings (left them unchanged from whatever was there, something like 213 and 220, respectively).

Ever since replacing the circuit board, the temp has been reading about 30 degrees higher than before. Mechanically, nothing else has changed. I am not getting any alarms, the fan is not kicking on, and I am not sensing a de-rate. I will check shortly to ensure the computer is seeing 180-190 temps as before. So, assuming the gauge is off by ~30 (as I am suspecting), how can I calibrate it?
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Old 09-29-2020, 09:33 PM   #2
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my dash gauge in my 444E is off.. its pretty good up to 190 or so.. then it stays in one place.. my computer can read 205 and the gauge still says 190... thern coputer goes to 206 and gaige quickly pops up to 212 or so ands stays there till the real temp goes down to like 198 or so then it falls back to 190.. I know there are supposedly 2 revisions of that circuitboard.. maye 3 but 2 that ive heard of... one that is pre-97 and one that is 97 up (3 box computers vs navpak)


the difference being the top scale on the pre 97 gauge was 230 and the top scale on the 97-up gauge is 280.. apparently the board controls how far the needle travels not the gauge itself.. my guess is that both gauge ijnserts are identical as far as sweep bit with different scales.. so the board needs to drive the newer gauige at a different algorithm..
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Old 09-30-2020, 05:43 AM   #3
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Find out if different sending units were used for different engines or years... Also whether temp reading ranges changed. A coolant temperature sensor is nothing more than a thermistor, or thermostatic resistor, to spell it out.

There are several different resistance ranges, which will change the circuit impedance at a given temp, thereby changing the gauge reading. Common low-end temps are 100, 140, 160, common high-end temps are 240, 260, 280, and ranges vary, meaning the temp change from one gauge mark to the next will vary.

It could be as simple as changing the sensor to get the correct range. But, of course, you need to determine whether there is indeed an overheating problem by shooting the area around the temperature sensor with an IR temperature gun.

If no problem exists, you might see if the ECM can be set to read different impedance ranges for different senders. It's possible yours was somehow set for an incorrect range. This might even be a switch on the circuit board, some speedos and odos can switched from mph to km that way. Also possible your board is currently set for C instead of F, which could also be switchable.
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Old 09-30-2020, 07:22 AM   #4
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Quote:
Originally Posted by CHEESE_WAGON View Post
Find out if different sending units were used for different engines or years... Also whether temp reading ranges changed. A coolant temperature sensor is nothing more than a thermistor, or thermostatic resistor, to spell it out.

There are several different resistance ranges, which will change the circuit impedance at a given temp, thereby changing the gauge reading. Common low-end temps are 100, 140, 160, common high-end temps are 240, 260, 280, and ranges vary, meaning the temp change from one gauge mark to the next will vary.

It could be as simple as changing the sensor to get the correct range. But, of course, you need to determine whether there is indeed an overheating problem by shooting the area around the temperature sensor with an IR temperature gun.

If no problem exists, you might see if the ECM can be set to read different impedance ranges for different senders. It's possible yours was somehow set for an incorrect range. This might even be a switch on the circuit board, some speedos and odos can switched from mph to km that way. Also possible your board is currently set for C instead of F, which could also be switchable.

by 2001 these panels use data communications to read the engine temp from the ECM and display it on the dash gauge.. so the trick is getting the ECM reading to match the dash.. it is the same sensor..
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Old 09-30-2020, 10:26 AM   #5
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Quote:
Originally Posted by cadillackid View Post
by 2001 these panels use data communications to read the engine temp from the ECM and display it on the dash gauge.. so the trick is getting the ECM reading to match the dash.. it is the same sensor..
Quote:
Originally Posted by Brad_SwiftFur View Post
Ever since replacing the circuit board, the temp has been reading about 30 degrees higher than before. Mechanically, nothing else has changed.
Obviously, something is different in this board, though. I remember something about Ford running a different thermostat temp in the 7.3 PS vs Navistar T444(E) vehicles. Navistar used 203s, vs Ford using one somewhere in the 190s (192 maybe?) Have also seen 160s and 180s available. It was mentioned the replacement part was Dorman. Seems to me this ought to come down to resistor(s) on the board, and their impedance value.

If so, it seems to me either the wrong resistor was used, or not enough were used. If it's all the same to the ECM, perhaps OP might experiment with soldering one or more resistors inline with the sender wire to the ECM. But an approximately 30 degree diference could still possibly be the difference between C and F scale. Maybe that's an option in ECM settings, maybe the boards are different between the two. Canadian model would be set for C scale, this is the case with most Canadian-market vehicles. Question is, would that be a different sensor, or a different circuit board, or both?
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Old 09-30-2020, 10:54 AM   #6
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but I thought his ECM reads the tenp correctly.. if you go messing with the temp sender going to the ECM just to make the dash gauge look better then you affect things like cold-weather fueling, CAP, de-rate, etc..



the ECM gets the temp from the sender.. the ECM opens up a DATA-LINK to the cluster on 2 wires and sends the data to the cluster.. the cluster reads the data and electrically fires the needles on the dash gauges..



its possible the OP's dash gauge module is bad..



as i mentioned there were 2 different temp gauges used in the busses.. one that topped out at 230 and the newer one that topped out at 280..


there were 2 revisions of these gauge cluster boards.. so if you installed an early revision board (one meant for a gauge that topped out at 230).. in a newer bus.. and then you plugged in a gauge that has a top scale of 280.. the result is that your dash gauge is always going to read high.....



the gauge and the board are 2 saprate pieces.. the gauges plug into the board..
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Old 09-30-2020, 10:58 AM   #7
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Quote:
Originally Posted by cadillackid View Post
as i mentioned there were 2 different temp gauges used in the busses.. one that topped out at 230 and the newer one that topped out at 280..

there were 2 revisions of these gauge cluster boards.. so if you installed an early revision board (one meant for a gauge that topped out at 230).. in a newer bus.. and then you plugged in a gauge that has a top scale of 280.. the result is that your dash gauge is always going to read high.....
Not sure why the sender wouldn't be different for the different range, but that's pretty much what I was getting at, difference in temp range reading.
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Old 09-30-2020, 05:05 PM   #8
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Having read the replies, I believe Christopher is correct, I am getting gauge readings consistent with the earlier version board, for a gauge printed with a "high" reading of 230; as such when the indicator points straight up, it would be in the 180 range.


It seems to me I could simply swap in an older style gauge and the reading would be correct.
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Old 09-30-2020, 05:37 PM   #9
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brad I was thinking the same thing.. seems like it cant hurt to try
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