Engine Temp Gauge Hot when engine is cold

[JRocket]

My 99 Explorer is reading WAY over HOT on the Engine Temp gauge and also showing Temp Warning on the Information Center, when the car is cold; shows VERY HOT immediately after starting when the motor is cold.
This started happening yesterday, with no prior indications of any problems with the sensor or the gauge.
It appears that the needle is trying to move even higher but I can't be sure.
Before doing very much research I've already replaced the ECT Sensor, and the behavior is still the same.

*Any suggestions as to what may be causing this, and what steps to take to test and resolve are greatly appreciated.

thank you.

 

[koda2000]

Bad coolant temp sender, shorted/grounded temp sender wire, bad coolant temp gauge.

 

[lobo411]

The temp *sensor* tells the computer how hot the coolant is. The connector has two wires.

The temp *sender* tells the dash gauge where to point the needle. The connector has one wire.

Did you replace the sensor or the sender?

 

[RandomNerd2000]

Sounds like a shorted sender, there's a sender, and a sensor, at least on the 4.0 SOHC I can verify.

 

[koda2000]

The temp *sensor* tells the computer how hot the coolant is. The connector has two wires.

The temp *sender* tells the dash gauge where to point the needle. The connector has one wire.

Did you replace the sensor or the sender?

On the 4.0 SOHC both have 2 wires.

 

[lobo411]

On the 4.0 SOHC both have 2 wires.

Yet another reason to dislike the sohc

 

[JRocket]

Thank you for all the replies.

Not knowing there was both a "sensor" and a "sender", I simply replaced the "obvious" one, the sensor. Then having read some of the replies here (thank you), I took another look at the "sender". I purchased a new sender and was in process of removing the old one, and in doing so found that the Thermostat Housing appeared to have been leaking around the sender (at the threads).

When I tried to remove the sender from the Thermostat Housing the brass insert in the Housing that the Sender was threaded into seemed to come loose from the Housing plastic, which isn't surprising since the whole area around the sender was green with corrosion, clearly indicating that's where it had been leaking (I was aware of a leak and wanted to find and fix it - Found It).

I purchased a new Thermostat Housing http://www.autozone.com/cooling-hea...n-water-outlet/176723_738647_0/?checkfit=true (I called our local Ford Dealer Parts Dept and they quoted $494.12 for the Housing with the Thermostat, the sender and the sensor. That seems quite high. Has anybody had good luck with a non-Ford Thermostat Housing? (see 1 below - I'll be buying a Second New Housing - returning the one I bought))

*the old Thermostat Housing is now out of the Explorer.

I have two issues at this point:
1.) before mounting the new Thermostat Housing back into the Explorer, I "lightly" twisted in the new sender and to my shock and amazement, the brass fitting seems to float around in the housing and move around, almost like the old fitting in the old Housing. Is anybody familiar with this? Shouldn't it be solid in the housing? Is there a "good" reason for it moving or is it just a bad part?

2.) while removing the old housing the tube piece of the Housing that the Bypass hose connects to crumbled and I'm quite certain some of the pieces may have fallen into the Bypass connector of the water pump. Also, I'm questioning if a piece of the Housing, one of the small tabs (about a 1/16" X 3/8") that fit into the hole of the engine on which the housing sits, that piece "may" have fallen into that hole in the block. Not sure if it did.

I'm planning on pulling the water pump off and inspecting it to ensure that if any debris did fall in, that it gets cleaned out. But for the other possible piece that may have fallen into the hole under the Housing, I'm wondering if there is any way possible to flush the system to ensure there's nothing there.

Any thoughts, suggestions, comments, are all welcome.

Thank You.