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2003 Ford Explorer temp gauge acting crazy!

Help… I recently purchased a 2003 Explorer. Two weeks after I bought it I found out the motor on the windshield washer water pump was shot. The dealership fixed it for free. About a week after I got it back when I was driving in the morning to work I noticed the check gauge light go on and saw that my temp gauge was pointed at HOT!! I pulled over and stopped immediately. As soon as I slowed down the temp gauge went back down to normal. It happened 2 or 3 more times and had it back at the dealership. They are stumped. They sent it to a Ford dealership and they couldn’t find anything either. They said they have checked everything and it is not overheating. They even put a thermometer on it while they drove it and it didn’t get over 205* I am surprised it didn’t do it to them because it happens almost every morning. I only work 4.3 miles from my house so its not like I am driving very far. It usually happens at about 3 miles. As soon as I see it going up (and I watch it ALOT!!) I take my foot off the gas and start to slow down or barely press the brake it goes right back to normal. Then it stays at normal the rest of the day. I have even filmed it to be able to show people what it is doing. Can someone please help me. Is it the sensor or the wiring or did the do something to it when the fixed the washer motor?

It sounds like you have air in your cooling system. Purge the air and see if that fixes the problem. If not…it could be a bad thermostat or temperature sending unit. Check the wiring as well…it could be loose on the sending unit. I would avoid the dealership and the Ford dealership as well. This is not rocket science here. Find a good independent mechanic in your area.

Check the Mechanic Files above for a good mechanic in your area. I agree with the air in the system comment or a bad sensor.

Hopefully these are cheap and easy solutions. Exactly how do I purge the air from the cooling system. How would air get in there in the first place. Thank you for your help. I really appreciate your input.

Here’s how to purge the air out of a cooling system.

Get the engine up to operating temperature.

With the engine idling, loosen the upper radiator hose clamp.

Take a small flat bladed screwdriver and insert it in between the upper radiator hose and the hose neck on the radiator.

Allow the engine to idle until all the air is purged out of the cooling system and nothing but coolant comes out.

Remove the screwdriver and retighten the hose clamp.

Shut off the engine.

Check the coolant level in the reservoir after the engine cools down.


I think it’s a good sign the dealership is helping you with this to such a degree. It is a 11 year old vehicle after all. I assume you mean the dealership that sold it to you. Good on them for being of such good assistance.

It does sort of sound like there’s air in the cooling system. I agree with the above posts that removing the air is a good first step toward a solution. If that doesn’t solve it, probably next thing I’d do is ask the shop to remove the engine coolant temp sensor (see the diagram above kindly provided by @knfenimore . It’s usually a gadget about the size of your thumb that just screws into the engine somewhere. The resistance vs temp curve can be measured in a heated water bath to see if it is calibrated correctly or otherwise acting up.

Not attempting to create alarm, but this symptom can also be caused by considerably more expensive problems, like a failing water pump, or even a compromised head gasket. But you have to go through the above first, before considering those.

If the heat gauge stays up and won’t come back down, and you think the engine might be overheating, be sure to turn on the passenger heater to max, fan to max. That should provide some cooling. If not, stop the engine immediately and tow the vehicle to the shop.

One gadget you might consider to buy – if you are looking for an excuse to buy something – is an infrared temperature meter. It’s sort of gun-shape thing you aim at something and it tells you how hot it is based on its color in the infrared spectrum. Those gadgets are fairly inexpensive, operate on batteries I think so they are portable, so you could bring it with you and if the gauge starts acting up, pull over and point the device at the upper radiator hose. That’s usually where the hottest water is. Best of luck.

There’s a lot going on here.
Firstly, regarding their having sent it to the Ford dealer, while I commend the used car dealer’s integrity, new car dealerships often simply do not want to bother diagnosing 11 year old cars. I’m not sure I understand why, but we get countless threads wherein the dealer should have helped and did not.

Cooling problems are not rocket science, but there can be a number of different causes. A “crazy” temp gage usually indicates air in the system. The cause of that them becomes the focus. The cause can range from

  1. a system unable to hold pressure (a system pressure test can often find this, unless it’s the radiator cap that’s the problem),
  2. a radiator cap unable to hold pressure,
  3. a partially clogged or internally coated radiator (in a used car it’s not unusual for the prior owner to have added something to plug a leak and the additive adversely affecting the ability of the radiator to dissipate heat),
  4. a bad cooling fan (or its temp sensor or relay),
  5. a cooling fan with eroded impellars (can be tested with a flow tester)… your car is really pretty young for this,
  6. a collapsed hos inner liner,
  7. or the coolant being overheated by a headgasket leak beyond its ability to dissipate the heat. This can and should be tested for. There are a few different ways to check for this. The best is a cylinder leakdown test, but if a simpler test such as a check of the coolant for hydrocarbons proves a leak, the leakdown test is unnecessary.

George’s suggestion to get an infrared thermometer is an excellent one. You should be able to find one for about $25, they’re super easy to use, and they can be used for other purposes too. I use mine to check in my house to find air leaks in the winter. I can guarantee that I’ve saved more in previously lost heat than the cost of the device.

My recommendation is to take it to a reputable local owned and operated shop for a diagnosis. With the diagnosis in hand, you can then return to the used car dealer if you prefer to have it repaired. IMHO it’ll be worth the few hundred bucks… or perhaps even less.

Hold the phone. This very thing happened to me and my '96 Camaro. I found this gem when I went to get the water pump replaced due to small leak out of the witness hole. I like to be proactive and it was cheap for my trusted mechanic to replace, Advanced Auto Tek in central Florida. He asked if I want a new thermostat. I said yes out of blind luck. My temperature was ALL over the place before, and rock solid after. The mechanic stated those thermostats only last 50~100k miles before they lose their calibration. He recommends replacing them on a regular schedule. I was going bonkers trying to get air out, new cap, flushes, electric fan checks, a/c relay and on. He said the water pump was fine short of weeping a little out of the front seal. It was still pumping fine. Those t-stats are subjected to a lot of thermal cycles on that spring. Get the correct coolant additive also. I’ve had a fair amount of corrosion fights with coolant.

The other scenario is if the radiator is partially plugged. This happened on a '76. This reduces the thermal rejection capacity of the radiator. The faster you go, more waste heat is generated. Therefore, when you slow back down, the temperature comes back down. The extra ram air at higher speeds did not aid heat rejection more than the extra heat loading. In those days, the fill cap was directly over the hot side of the radiator, and visual inspection was possible. Maybe a camera could be utilized by the shop boys. I don’t know of anyway to test for a partially plugged radiator, while in the car. In those old days, one could open the end caps and re-solder. These days it’s one time seal, then total replacement. I’ve replace a-many radiators in the last decade, mostly to leaks.

Have you checked how much road kill you have on the front of your radiators? A coated front radiator (which will be the air conditioning one) will have the same effect as internal plugging. In my experiences, I have had a lot of road kill debris in-between the two radiators. Usually the a/c radiator can be loosened enough to see in-between.

OH! One other ouchie-gotcha that happened to me. That fan clutch that is between the plastic blades and the drive belt. I had that go bad on a '00 Mountaineer. I can’t recall if the '03 is a belt or electric fan. That is not cheap, but it can fail. It will stay ‘loose’ when the spring in front is cold. When heated, that spring is suppose to tighten up the internals so that the fan slips less, which pumps more air. Those go bad.

There is no testing any of these problem parts. Just keep swimming! Take it one at a time.

One could try a flush cleaning treatment first, then replace the t-stat. None of these can be tested as far as I know, or the cost to test exceeds replacements. Start with the low dollar prices and work upwards.


Actually, a T-stat can be easily tested with a Pyrex vessel, a cooking thermometer, and a hot plate. But you’re right, the cost of the test probably exceeds the cost of a new T-stat.

A radiator can be “mapped” using an infrared thermometer to verify clogged tubes. You’ll see the temp drop when you aim at the spots beneath the clogs. Very large differences between the upper areas and the lower areas while the car is idling often are indicative of badly coated radiator internals.

I like all your points, though. I like your style. Just wanted to pass along those test protocols.

It is important that the shop is made aware that the temperature gauge only goes to hot during the first few miles/vehicle warm up. Otherwise a lot of time will be wasted waiting for the vehicle to overheat.

Most of the time when I discover this by chance, (the customer only states that the vehicle overheats every day) the problem is a delayed opening of the thermostat. Replacing the thermostat should correct this, after all it did suffer some trauma if it was run low on coolant due to the leaking water pump.

My vote is for the thermostat and just my 2 cents, but I consider the T-stat to be a maintenance item that should be swapped out about every 4 or 5 years. Cheap insurance is the way I look at it.