Erratic oil temp readings

I installed an aeroforce gauge to read my oil temp and pressure. Everything was working well for a few months and then recently my oil temp readings have been very erratic. It jumps up and down from -40 up to 180 degrees. I've checked my grounds and wires/connections and everything seems fine.

I did not solder my connections and only used crimp connectors. I also used solid copper wire, not stranded wire for the temp sending unit (i've always used stranded wire but ran out). Should i solder everything up, do you think there is a resistance issue?