[Steve91T]

So I've been putting some miles on this engine after it sat for years and I've got a problem that I would like some help with. It's got a new water pump and thermostat, for now the heater hoses are capped off. I'm running a manual fan switch. The water temp gauge is in the drivers should side head.

So everything seems normal except for some reason if I drive down the highway my water temp will drop to about 150 degrees. It acts like the thermostats is stuck open. Yesterday I pulled the t-stat and put it in a pot of water and watched it. It started opening at 180 degrees like it should, then closed when it cooled down.

So why is this happening?

[Steve91T]

I pulled the water temp sender. I heated a cup of water to 190 degrees and dropped the sensor in and watched the gauge. It climbed quickly to exactly 190 degrees. I measured the temp of the water using a very accurate instant read meat thermometer.

So, something must be hooked up wrong. Incorrect heater hose routing or something? Would that cause this?

If I'm at a light and the temp gets to 200, within minutes of cruising down the road, it'll drop to 150 or so. Something is wrong, just not sure what.