Coolant temp gauge bad or ecu failure?

[matthew gilland]

Hello,

 

I have a late 1999 24 valve sport model appears to be 4 wheel abs, just extra information. Have edge comp, S&B cold air intake, 5 inch turbo back straight pipe, and RV injectors. Rest of truck is stock.

Anyway, I am just curious as to if it is normal for the stock temp gauge on the dash to be at 140*F on a cold engine in the summer. Sits for about a week then drive it off and on this summer 2022, temps reaching high 90*F. But yeah, when I go to use the truck after starting the temp gauge is already reading 140*F. I know that is not normal but I just would like a 2nd opinion. I also do have the Mopar1973Man High Idle/Eco Switch installed. It is switched off the whole time. I even changed the coolant temp sensor right by the t-stat housing. 

Is it possible the eco switch has died? Or is there a second temp sensor. It looks like the 12 valve has two sensors but not sure about the 24 valve. 

Or is it an ecu failure? I did read something about the gauge cluster is operated by the ecu so that is why I added this option.

 

Any help would be much appreciated. 

Thank you for your time!

[wil440]

I just turned the ignition on to check mine which is a 98.5, gauge goes straight to 140F with ignition on engine off, been out to get de ionised water this morning so engine isn't overnight cold and when I just started engine then it read what the temp was but not with just ignition on if that helps

[Mopar1973Man]

Unplug all mods. Then re-test. If it's still showing incorrect then test your wiring. Typically the ECT and IAT should be the same at key on and no start.

[matthew gilland]

@Mopar1973Man

Please excuse my late response. 
I unplugged the mods and put it back to stock. No change. Turn the key and goes straight to 140*F on the instrument cluster. I have noticed that the truck does get hotter faster according to the temp gauge which is odd. I have the 195*F tstat installed because of MN winters. And noticed the temp gauge goes over 200*F before going down some once the tstat opens and then the temp goes just under the 190*F mark. 

Not sure if this is all normal. But truck is 20+ years old. Just don't want to end up stranded on the side of the road for overheating.

 

I am tempted to get that scan gauge 2 module to see what the computer is actually reading for temps. 

 

[wil440]

As I posted before.  My truck goes to 140f with key on engine off, start it and it then reads temp.

With a 190f thermostat 200 before it opens is OK just as long as it drops back to 190f PDQ 

Do you know anyone with a scanner that reads live data? That would show you what's going on but I think you are fine. 

 

I take it if you drive it hard pulling a good grade temp is 190f or so ? I have a 190 stat and working hard mine gets to 197 ish and doesn't go higher for very long at all, I did see 200 Tuesday pulling the T Trailer in another thread but only for a few seconds and that was on a long 11% grade in 2nd gear

[Mopar1973Man]

Temps are normal. I run 193 to 197°F typically and could see 215 to 220°F before fully lock of the fan then it kicks I cools to 197°F. Then unlocks. I know once past 225°F the cluster will trip the check gauge light, chime and the gauge will peg at 240°F. It will not display any temp other that 240 till it drops below 225 again.

[LorenS]

On 9/14/2022 at 5:53 PM, matthew gilland said:

am tempted to get that scan gauge 2 module to see what the computer is actually reading

OBDLink LX is great if you don't want a semi-permanent gauge.

[Mopar1973Man]

Or ODBLink MX which is the newer series.

[hdpwipmonkey]

The OBDLink is a great little tool to have in your toolbox.  You can use it on multiple vehicles to read live data, scan for codes, and reset them.  Well worth the price.

 

 

https://www.amazon.com/OBDLink-Bluetooth-Professional-Grade-Diagnostic-Performance/dp/B07JFRFJG6/ref=sr_1_2?crid=3EB5A5STOMZBE&keywords=obdlink+mx&qid=1663602077&sprefix=obdlink%2Caps%2C164&sr=8-2