Can someone educate me on online 6 coolant temp sensors

[chevyguyase]

I have the same coolant sensor hole set up. I can not get a correct reading out of the coolant temp sensor hole in the head. I think because it is to close to the exhaust port. It reads way to hot. I've tried 3 different gauges. I do have my mechanical under dash gauge hooked up to the hole in the head and it constantly reads 250+ degrees. I have to keep my EFI temp sender in the hole in the thermostat housing because I need an accurate input for the ECM. They make a thermostat housing with 2 sensor holes in it, but can't get my hands on one. They also make the part that the thermostat housing bolts to with a sensor hole in it, I can't find one of those either.