weirdo issue with autometer water temp gauge.

[b00stinbmx]

i have a stock KA gauge temp sensor in the rb20 as well and a autometer water temp gauge with the sender bunged into the end of the waterpipe there before the top hose for the rad. today on a long trip from CT to NH i noticed it acting up pretty weird. my gauge cluster temps NEVER changed. they always stayed at half or a lil below half but the autometer gauge started around 190 and slowly worked its way up to like 210. then after longer almost all the way pegged to 250. i stopped to check the car and nothing, no leaks, no overheating.

Like a dumbass last night when i was messing with some wiring i did notice i crossed the wires for a second. i had the ground and 12v hooked up wrong it didn;t seem to ruin the gauge cause when i started up the car and drove it for the first hour or so everything was normal. the only other thing that i can think of is is the metal becomming hotter than the actual coolant? and maybe the hole that the sender is sitting in isn;t drilled properly? im really stumped here or maybe the gauge is just messed up but theres no way im running at 230-240ish temps and the entire time the stock cluster didn;t move a touch, and in the past it worked fine when i had some overheating prob.