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How do I replace a thermostat in a 1999 Ford Explorer?

When I driveThe temperature gauge constantly goes from cold to hot.

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James from Auto.Repairs
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I'am feeling that your issue is not really with the thermostat my friend. what your describing seems to be the coolant temperature sensor.
And or a loose connection to the sensor How do I replace a thermostat in a 1999 Ford Explo - 48121ee4-0616-4184-b990-49f490eea9c0.jpg fa29c095-9038-43aa-aeee-f9ad43acb595.jpg

Try turning the key on engine off and look at the coolant gauge
now go out and under the hood it should be in the thermostat housing where the thermostat goes to you should see the #1 picture with 2 wires going to it if you unplug it and go back into the car and look at the gauge it should be in the red hot zone.
if not then your gauge has a short to it lightly with your palm of your hand rap on top of the dash nearest to the gauge and see if it tries to go up if it does then most likely it is a short in the cluster or harness.
and if when cts is unpluged and it goes all the way in the hot zone and when you plug it back in and it goes back into the cold and stay there should be that it is fine just loose connector or needs cleaned if when you wiggle wires and the needle goes up and down then you need to replace the plug and I would still suggest replacing the coolant temp sensor as for it may have been shorted do to the loose connection.

Posted on Sep 08, 2014


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Drain the cooling system at the radiator, the thermostat is located where the upper radiator hose attaches to the engine, remove the hose, then remove the water neck exposing the thermostat, remove and replace the same way the old one came out, then install the water neck and hose, tighten all fasteners, clamps and refill cooling system to manufacturer procedure to properly "burp" the system.

If you need further help, I’m available over the phone at

Posted on Sep 08, 2014


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Posted on Jan 02, 2017


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SOURCE: Temperature gauge shows hot

head gasket does the overflow bootle have bubbles in it when idleing warm if does most likey rear head gasket.

Posted on Jan 06, 2009


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SOURCE: 1999 Dodge Durango NO HEAT

Bad NEW thermostat? I had the same problem on my first generation Dakota. The problem for me turned out to be the DODGE thermostat I used to replace the old Dodge part. I went and got a Stant from local auto parts store using the standard temperature spec and quit shivering the next time I drove it. I hope that helps!

Posted on Jan 17, 2009



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SOURCE: Temperature Control not working on 1999 Ford Explorer

Sounds like your temperature actuator is not moving or your temp door is broken. On max a-c ,coolant is shut off to your heater core allowing only cold air in.

Posted on Jan 26, 2009


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SOURCE: 2001 suzuki swift - thermostat replace?

Suzuki thermostats, more often than not, tend to fail OPEN when they have been overheated - which is a good thing! If they failed shut, you would really cook the motor. Change the thermostat. Also, find the cause of the initial lack of coolant.

Posted on Sep 21, 2009


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SOURCE: The temperature gauge on my 1999 Dodge Ram 1500 is

Check the gauge by holding in the trip odometer reset button and turn key to run,hold button for 10 seconds this will iniate a diagnostics on all the gauges,and lights if gauge doesn't move during this test replace gauge,if it does move then check the wires on the plug at the engine coolant temp sensor (ects) you can check the sensor by using a ohms meter by unpplugging it and check ohm's or resistance when cold and then start engine as the engine warms up the ohm's reading should gradually lower as the sensor is a thermister and as it warms up the resistance will drop.

Posted on Jun 05, 2010

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I need the easiest possible directions to replace the coolant temperature sensor in my 1999 Chevy Lumina ltz 3.8 v6 car please.

The coolant sensor temperature is usually found just beneath the cylinder head, on the engine block.

You just disconnect the 1-2 wires and then undo it with a wrench.
The sensor will look like one of these:
1999 Chevy Lumina ltz 3 8 v6 coolant temperature sensor Google Search

Just be aware .. you may have TWO such sensors on your vehicle.

One sensor (usually with 3-4 electrical pins) is near the thermostat and works in conjunction with other sensors to regulate fuel/air according to engine temperature.

The other type of sensor is in the block near the cylinder head. It sends a signal to the temperature gauge on your dashboard ONLY. If your temp gauge constantly reads too hot or too cold .. this one is the culprit.25939754-r0ibht2u2t2rhetbyfvb2pry-5-0.jpg
If it's a running fault .. speed .. rough running .. fuel. It may look like this:

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I have a 1998 Ford Explorer Eddie Bauer 5.0 V8 and the temp gauge in dash goes all the way to hot after restarting engine but info panel in console says the engine temp is ok. It seems to run like normal...

Although the Explorer I had didn't have the same size engine, I did have a similar problem. Start with looking up the location of the temperature sensor unit. I little Google search turned up a few youtube videos and some links to new parts ranging from around $20 and up. Of course the price is only dependent upon the application so the lower cost one's could be for the smaller displacement models. Judging by your description and the fact that you drove that distance without the engine seizing, this may be the culprit. Good luck.

Jan 31, 2014 | 1998 Ford Explorer

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Temp gauge is very erratic from cold to peg hot. engine not hot

Sounds like the temp sending unit is faulty.....

Nov 10, 2010 | 2000 Ford Explorer

2 Answers

Why does my thermostat gage keep going from cold to hot constantly

I really would like some clarification on that.
If your inside gauge seems to read cold for a while and then just goes hot it generally means either the gauge is sticking or much more likely the thermostat is sticking because it is about to go bad. Actually it has gone bad already if it is staying closed. Now most thermostats have a little bypass hole to let air and small amounts of water through to circulate all the time. this allows the hot water to actually reach the thermostat when it is mounted somewhat from the heat source. If that hole becomes plugged it will give the same effect since the entire engine has to get hot before the thermostat can even start opening. Once it starts opening it gets a rush of super hot water that slams it wide open.
If you don't notice any problems with the engine like water boiling over or any other strange behavior then it is likely the actual gauge in the dash sticking or the sensor malfunctioning.
What you want to do is take a laser temp gauge and get a temp reading off the radiator when the engine is reading hot. this will give you an idea whether or not it is lying to you. bring it over and ill lend you mine. ;)

Apr 19, 2010 | 1999 Acura Integra

1 Answer

Temp gauge goes up to hot then back down, up and down...

That is very possible.Your radiator could also be plugged,You water pump could be could be giving out or the head gaskets are bad..Those are all worse case scenario's But yes the thermostat could be the problem..I'd start with that then make sure your clutch is working properly..Hope this helps you and have a great day

I’m happy to assist further over the phone at

Apr 02, 2009 | 1999 Ford Explorer

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Explorer 4.0l 4x4 temp gauge goes to cold when heater turned on

You are going to have to replace the engine thermostat.

Jan 23, 2009 | 1999 Ford Explorer

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Temperature Control not working on 1999 Ford Explorer

Sounds like your temperature actuator is not moving or your temp door is broken. On max a-c ,coolant is shut off to your heater core allowing only cold air in.

Jan 16, 2009 | 1999 Ford Explorer

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