Engine Temperature

[ODZKing]

Is there a way to get a fairly accurate reading of engine temperature other than the sensor in the water pump?
Short story is: my dash gauge is not working properly, so I connected an aftermarket digital gauge.  The kit came with its own sensor but I didn't want to remove the original one from the pump because I DO plan on getting the original working, just not right now. And I don't feel comfortable driving without knowing the engine temp.  The original gauges are 5 volt and new one is 12. It was reading about double connected to the OEM sender.
So just for the hell of it, I connected a potentiometer to the feed line and to my surprise, it works.  BUT, I have to calibrate it.
So, if I start the car and let it run for just a few minutes with the radiator cap off, then take a reading of the fluid, will that be a relatively accurate reading? Or is there another way of doing this?   

[A383Wing]

which engine? Big block or small block? If big block, you should have another plug in housing. You cannot connect after market gauges with stock senders...not calibrated

[ODZKing]

Big block and no, not going to fool with it further.
And it works fine, just need to adjust the digital one to read properly.
Don't need to launch the space shuttle here, just need to know is it 180 or 280.   

[John_Kunkel]

A big block water pump housing should have an unused port in the top that is plugged, use it to install the aftermarket gauge.

An infrared thermometer from Harbor Freight is a handy item to have, measure the temp at the top tank on the radiator.

http://www.harborfreight.com/infrared-thermometer-93984.html

[ODZKing]

Thanks John, but once again that unused port will not work.  By the time I size down with fittings the sender won't be sticking into the pump.

That is the conclusion I've come to as well, top of the tank should be close and all I need is one reference temp to set it.

Thanks, that answered my question.

[John_Kunkel]

You need what's called a "face bushing", this will reduce the thread and allow the sender bulb to reach the coolant.

[ottawamerc]

What about just drilling and tapping in another port?

[ODZKing]

A lot to go through for something that is temporary.
The varible potentiameter is in there and works great.  Just need a calibration point.
Thanks.