Coolant Temperature Gauge Woes...

[YBC Offroad]

Hey everyone. It's been a while since I've been back on this forum. Backstory to the problem I'm currently experiencing. Family member was driving my m925a2 truck and killed the battery disconnect on the dash instead of my key. That took out basically everything electronic. Generator, ctis system, all electric gauges, fuel shutoff solenoid, etc. Got everything replaced a while back. (Truck sits a lot). Was driving it and noticed coolant temp would slowly creep up to around 220 on gauge. Grabbed my temp gun to find out that the engine was only at 160 degrees. Ordered a thermostat and new temp sender (engine has been overheated before so I didn't know if temp sender was damaged). Found a failed open thermostat and replaced the temp sender while I was in there. Got it full of coolant and went on a drive. Now the gauge will read almost 240! But in all reality I used the temp gun and it's at a smooth 185-190 after 10 miles down a highway. So I got a new gauge, new temp sender, and I visually inspected the wire and found no rub spots or bad spots. I unplugged from both sides and checked for resistance to ground and had nothing. I'm kind of confused at this point as it's a pretty basic system. Was wondering if I could plug that temp sender into my trans temp and see what that gauge reads? All other gauges are working normal. Maybe I just got a bad gauge.. they were all from eastern surplus supply. Hopefully this is enough info for you guys to help. I'm around every evening after 430 pm and am available to try any ideas you guys have. Thanks!

 

[Mullaney]

Hey everyone. It's been a while since I've been back on this forum. Backstory to the problem I'm currently experiencing. Family member was driving my m925a2 truck and killed the battery disconnect on the dash instead of my key. That took out basically everything electronic. Generator, ctis system, all electric gauges, fuel shutoff solenoid, etc. Got everything replaced a while back. (Truck sits a lot). Was driving it and noticed coolant temp would slowly creep up to around 220 on gauge. Grabbed my temp gun to find out that the engine was only at 160 degrees. Ordered a thermostat and new temp sender (engine has been overheated before so I didn't know if temp sender was damaged). Found a failed open thermostat and replaced the temp sender while I was in there. Got it full of coolant and went on a drive. Now the gauge will read almost 240! But in all reality I used the temp gun and it's at a smooth 185-190 after 10 miles down a highway. So I got a new gauge, new temp sender, and I visually inspected the wire and found no rub spots or bad spots. I unplugged from both sides and checked for resistance to ground and had nothing. I'm kind of confused at this point as it's a pretty basic system. Was wondering if I could plug that temp sender into my trans temp and see what that gauge reads? All other gauges are working normal. Maybe I just got a bad gauge.. they were all from eastern surplus supply. Hopefully this is enough info for you guys to help. I'm around every evening after 430 pm and am available to try any ideas you guys have. Thanks!

.
So, it sounds to me like you have already metered the wires and I saw "visual inspection" too. If you happen to have a spool of 14 gauge wire, what about going out back and disconnecting the sending unit, add attach your new wire, then go back behind the "panel" and hook the other end of your wire to the gauge.

That way you have replaced (eliminated) the wire completely. Just out the door. Loose wire - Just for Problem Determination.

Also need a big alligator clip to clamp to the battery ground under the seat and another to clamp onto the ground on the gauge panel.

 

[YBC Offroad]

.
So, it sounds to me like you have already metered the wires and I saw "visual inspection" too. If you happen to have a spool of 14 gauge wire, what about going out back and disconnecting the sending unit, add attach your new wire, then go back behind the "panel" and hook the other end of your wire to the gauge.

That way you have replaced (eliminated) the wire completely. Just out the door. Loose wire - Just for Problem Determination.

Also need a big alligator clip to clamp to the battery ground under the seat and another to clamp onto the ground on the gauge panel.

Will do. I'll update tonight or tomorrow morning with the outcome. Thanks

 

[ericp351]

Hey everyone. It's been a while since I've been back on this forum. Backstory to the problem I'm currently experiencing. Family member was driving my m925a2 truck and killed the battery disconnect on the dash instead of my key. That took out basically everything electronic. Generator, ctis system, all electric gauges, fuel shutoff solenoid, etc. Got everything replaced a while back. (Truck sits a lot). Was driving it and noticed coolant temp would slowly creep up to around 220 on gauge. Grabbed my temp gun to find out that the engine was only at 160 degrees. Ordered a thermostat and new temp sender (engine has been overheated before so I didn't know if temp sender was damaged). Found a failed open thermostat and replaced the temp sender while I was in there. Got it full of coolant and went on a drive. Now the gauge will read almost 240! But in all reality I used the temp gun and it's at a smooth 185-190 after 10 miles down a highway. So I got a new gauge, new temp sender, and I visually inspected the wire and found no rub spots or bad spots. I unplugged from both sides and checked for resistance to ground and had nothing. I'm kind of confused at this point as it's a pretty basic system. Was wondering if I could plug that temp sender into my trans temp and see what that gauge reads? All other gauges are working normal. Maybe I just got a bad gauge.. they were all from eastern surplus supply. Hopefully this is enough info for you guys to help. I'm around every evening after 430 pm and am available to try any ideas you guys have. Thanks!

You may be relatively OK, with the sender out of calibration for your voltage, or in general. If so- now your gauge reads realitive- to the right= hotter, ignore #'s. A workable solution is to solder in line a small resister to match up sender to your gauge #'s. Cost pennies- I pulled one from a Am-Fm Radio. I did this to calibrate- ended up about 6 deg. Too Hot on gauge, and left it (full scale), as it keeps me honest. Common trouble- 20+ year old Gauge , aftermarket sender, old wires, old volt reg., etc. It would be a mirical for all your/ our random parts to land perfectivly calibrated!

 

[YBC Offroad]

All right everyone sorry for the delayed reply. So I over layed a wire with no change. I cleaned the thread tape I had on the temp sensor off and re installed. No change. I then added a ground to the temp sender body right to battery ground along with doing the same for the gauge.. No change. Gauge reads accurate till about 150 degrees then it just takes off. When the engine warms from 150 to 160-165, the gauge is reading above 200. So odd. Any other ideas? I'm all ears

 

[ericp351]

All right everyone sorry for the delayed reply. So I over layed a wire with no change. I cleaned the thread tape I had on the temp sensor off and re installed. No change. I then added a ground to the temp sender body right to battery ground along with doing the same for the gauge.. No change. Gauge reads accurate till about 150 degrees then it just takes off. When the engine warms from 150 to 160-165, the gauge is reading above 200. So odd. Any other ideas? I'm all ears

Simply check that your sender is linear. See what the resistance change per 10 deg is cold, then warmer, then warmer, than at operating. If linear- your sender is fair (responds ok, calibrated questionable, or good) . Then look to gauge. If not linear- you got bad sender. The wiring is simple, and you implied well surveyed. As I said above- when you got OK parts, you can then calibrate. You need only-1) constant volts. 2) Linear (+ grounded) sender. 3) good wires. 4) good gauge. Then calibrate as reqd.