Bad needle thermometer?

Is is possible for needle style thermometers to go bad? I bought one at the local homebrew shop a few months back and have loved the simplicity. However, after the last 5 batches I'm doubting its accuracy. I usually get around a 72-75% brewhouse efficiency, but my last 5 batches have been around 55%. I haven't changed anything in my process. I just brewed an IPA that was suppose to be a 1.067, but came out to 1.051. The only thing I can think of is a bad thermometer.

My garage thermometer measured 70 degrees, but my beer thermometer is registering 83. I also checked it to my outdoor thermometer. The outdoor temperature is 68 and the beer thermometer is registering 80. That seems to be a pretty big discrepancy. I usually mash around 150-152, so if it's actually 10 degrees cooler I'm out of the efficient mash range. The funny thing is that when I stick the thermometer in the freezer it reads 28. Next time I'm at the brew store I'm going to bring the thermometer and compare it's ambient temperature to another thermometer.

I'm just curious if anyone else has had their needle style thermometer go bad? I really hope that is the case, I don't understand why my efficiency has gone to crap. I'd hate to tear my mashtun apart over a bad thermometer.

I currently have the thermometer sitting in my room and it's registering 95. There's no way that it's above 70 right now.

The ones we sell have a nut on the back the allows them to be adjusted. Maybe yours does as well.