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Coolant temp all over the place.

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Did a search and couldn't find exactly what I am experiencing. Sorry if this is in the wrong spot or has been asked a million times.

Was having a coolant temp issue so changed sensor and thermostat. Now My coolant temp is reading all over the place constantly. Always bouncing around. It shows anywhere from 32 degrees up to like 280. The dash gauge goes nuts and my Edge monitor goes nuts. They don't always show the same temp either. It'll bounce all over the place, and then settle on 32 degrees and stay there a while and then goes right back to bouncing around. Unplugged my temp sensor and the gauges still do the same thing. Any ideas what the heck is going on?

Thanks!

EDIT: I have an external coolant temp sensor laying around from a previous build that I'm thinking about throwing on quick to see if it's actually changing temperatures or if it's somewhere in the wiring. Might do that over the long holiday weekend.

EDIT2: added picture of codes I ran. Couple codes had no description. One code is for coolant temp too high, one is for coolant temp sensor circuit too low. Maybe that's the cause of the issue?
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I read over your post too fast, definitely sounds electrical. I’d start with trying another sensor, then start tracing wires to the ecm looking for a short. Do you have any codes?
 

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Discussion Starter · #5 ·
I read over your post too fast, definitely sounds electrical. I’d start with trying another sensor, then start tracing wires to the ecm looking for a short. Do you have any codes?
No check engine light, but the edge monitor shows a couple codes when I run diagnostics. Don't remember what they are off the top of my head. I'm at work right now, I'll rerun diagnostic and write codes down on break.
 

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Did you warm it up all the way with the cap OFF and get it 100% full to the cap? All air out.
 

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If you ru n out pf tricks replace the sensor, after that clean all the grounds on the fenders and engine block
 
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