Strange OVERHEATING Issue

Saint · Nov 16, 2013

94 Mustang 3.8L
-Water pump new from ford
-Head gaskets replaced by sound mechanic

Here's what happens...Car can be completely cold, I crank it up.. Temp gauge says cool for at least 8minutes then it gets to normal temp then overheats....when it overheats smoke comes from the upper radiator hose around the radiator, not at the thermostat housing.

Here's where it gets weird.

3 minutes after overheating I get in the car....Turn the key... and the temp gauge it back "towards the N" like it never got hot. Also the coolant in the radiator is not hot either. So here is what I'm thinking....the thermostat is not opening and the coolant never circulates through the engine which would explain the coolant not being hot?

Another question: How is the temp gauge working with no coolant flowing through the engine (if that is the case) is it reading air?

Here's what I've done
-Flushed radiator (properly)
-Checked water pump weep hole
-Removed water pump pulley to check for grinding sounds (no grinding)

I know most of you are probably think why the hell didn't I change the thermostat already...well it's dark outside now.

Saint · Nov 16, 2013

help

96blak54 · Nov 17, 2013

Maybe she needs a burp? Did this just come on suddenly or was their some engine work done?

Saint · Nov 17, 2013

Came on suddenly the temp gauge had never worked on the car, and I know 94/94's are notorious for failing clusters. I checked the car with a temp gun the day I bought it and temp was 197 after driving for 1 hour. The first time it overheated the temp gauge magically started working. It's only overheated twice.

Saint · Nov 17, 2013

Update, replaced thermostat, began to burp system, Saw smoke, Upper radiator hose was leaking slightly where it meets the radiator....Fan WAS NOT ON, Turned on A/C, Fan came on immediately.

Replaced Engine Coolant Temperature Sensor (ECT) and Replace Coolant Temperature Sensor.
Check Engine Light (CEL) has now turned off
Fan now comes on without turning on the A/C

Leak coming from upper radiator hose where it meets the radiator.

Diagnosis: Small Pin hole in Radiator = System not holding pressure (can also see where someone put sealant around the hole)

Will replace next weekend when I have time and update.

Cheers