So I have an '87 pickup that is overheating after 10 minutes of normal driving and no heat comes from the vents. It has a relatively new aftermarket radiator. I've flushed the system and replaced the thermostat and gasket. I have a feeling it's the sending unit but the heater issue makes me think there's another possibility. The needle will rise when it should but eventually drops again. It will start boiling over into the overflow bottle loudly. Any ideas would be great.

 

Check the heater core cable. It's a flimsy looking metal cable with a loop at the end. Have someone toggle the heater switches inside and you can see it move under the hood. If not, it may be that the heater core metal pipe may be bent. Did this just happen recently?

 

It's right under this hose

 

Yeah it started a few days ago. I'll check that but could that be causing the over hearing issue?

 

I remember having the same issue. I also cleaned out the heater core

 

If it's boiling over into the overflow tank, it's getting too hot. No need to blame the sending unit. Sounds like something is blocked in the circulation. Double check the thermostat is in right. Also check for a bubble in the cooling system. These things are notoriously hard to "burp" all the air out when replacing the radiator or coolant. A trapped bubble will give you symptoms like you are seeing. There are some posts on this board for how to burp the air out.