Overheating

Tiny
ROBERTBARNES62
  • MEMBER
  • 1999 FORD EXPEDITION
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I was driving today with the AC on and noticed when I stopped at a light my truck temperature gauge shot up to the hottest on the display. A red light also came on to indicate it was too hot. Once I started going again it cooled off instantly and the gauge returned to normal temperature. I checked the oil to see if there was any coolant in there and there was not. I checked the coolant to see if there was either lack of coolant or oil in my coolant and neither were true. So I am wondering what else could make it overheat and act like that?
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Monday, July 2nd, 2018 AT 12:36 PM

41 Replies

Tiny
STEVE W.
  • EXPERT
The cooling fan is not operating like it should. In this case it sounds like the fan clutch may have failed. The other item would be that the radiator is partially blocked. But if you started moving and it cooled back down I would check the fan clutch first.
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Monday, July 2nd, 2018 AT 12:58 PM
Tiny
ROBERTBARNES62
  • MEMBER
Okay, how do I check to see if the fan clutch is bad?
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Monday, July 2nd, 2018 AT 1:14 PM
Tiny
STEVE W.
  • EXPERT
You have actually done the test already but did not finish it. The test is to run the engine until it gets up to operating temperature, then look/listen for the fan to operate. You can also shut the engine off at that point and reach in and try to move the fan. It should not move easily with the engine hot. However, the symptom you listed is an A-plus indication of a failed fan clutch. While in motion the fan will throttle itself on/off in response to the engine temperature. There should be plenty of air while in motion, when you start to slow down and stop the fan should engage fully to pull air through the radiator.

The only test with a cold engine is that it should spin easily, if it does not it is locked up and needs replacement. In your case that will not tell you anything as yours is not locking as it should.
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Monday, July 2nd, 2018 AT 3:16 PM
Tiny
ROBERTBARNES62
  • MEMBER
Thank you so much. I just ordered a new fan clutch and will install it soon. Thank you
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Monday, July 2nd, 2018 AT 3:20 PM
Tiny
DANNY L
  • EXPERT
Hello, I am Danny.

Unlike an electric fan which is controlled by sensors and the PCM ( a vehicles computer). A fan clutch is a viscous coupler controlled mechanically by the fans RPM's with the engine running. The fan clutch is an item that wears normally and is subject to replacement after time/wear. Mechanical (viscous) fan clutches are more effective at lower speeds when airflow is not as much as freeway driving. I have attached a tutorial the shows you its function. Hope this helps and feel free to ask us questions if needed. Can also include fan clutch replacement instructions if needed. Danny-

https://www.2carpros.com/articles/how-a-clutch-fan-works

https://www.2carpros.com/articles/fan-clutch-symptoms
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Monday, July 2nd, 2018 AT 8:56 PM
Tiny
ROBERTBARNES62
  • MEMBER
So I replaced my fan clutch and it still overheated. I found that the thermostat was sticking so I replaced that as well. It worked fine for two days. Just now I drove to work and as I pulled in the drive way at work the temperature shot up again. I turned the AC off and the temperature dropped back down to normal temperature. I then parked in a parking space and turned the AC back on just to see if the temperature would shoot back up but it did not. Any suggestions on what could be wrong? The water pump is less than three months old, the fan clutch and thermostat is two days old. What should I check or do next? Thank you in advance!
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Friday, July 6th, 2018 AT 11:39 AM
Tiny
STEVE W.
  • EXPERT
Okay, something is strange. How is it overheating? Actually boiling and spewing coolant or just the gauge/light saying it is hot. Turning off the AC should not make the temperature drop real fast, it would drop a bit without the extra heat but not that much.
I would probably use either an IR thermometer to check the temperature or add a mechanical temperature gauge to verify what the vehicle is seeing. If the trucks gauge&light show hot, but the mechanical gauge showed "normal" temperature. I would look at the sending unit and wiring to make sure there is not a rubbed wire or fault in the sending unit.
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Friday, July 6th, 2018 AT 12:50 PM
Tiny
ROBERTBARNES62
  • MEMBER
It did not boil or spew over. It just showed hot on the gauge. This happened as I slowed down to go over a speed bump, at that time I turned the AC off and it returned to normal temperature. Where on the motor do I check the temperature with an IR Thermometer? How do I install a mechanical temperature gauge? Lastly, where is the sending unit on the engine? Just thinking is there anyway air in the system could cause this? I ask cause when I replaced the thermostat I lost some coolant.
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Friday, July 6th, 2018 AT 1:14 PM
Tiny
STEVE W.
  • EXPERT
You said it worked okay for two days after you replaced the thermostat. That tends to make me thing you have a sending unit that either is failing or wiring to it.
You can check the temperature on the radiator hose or the thermostat housing, basically a spot where the coolant flows but is not bright and shiny. The mechanical gauge would depend on which style you use. Most use a probe that goes into the factory holes in the cooling system. The attached are the two sensors that could set the light/gauge off. The first is the engine coolant temperature sender. It screws into the lower intake manifold on the passenger side. The other is the cylinder head temperature sensor. It screws into the cylinder head behind and below the thermostat housing. Being yours is a 1999 it may only have the cylinder head sensor but the early ones had both.
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Saturday, July 7th, 2018 AT 3:32 AM
Tiny
ROBERTBARNES62
  • MEMBER
So I topped off the coolant and drove the SUV for the past two days just to see what it would do. The first day it drove fine and today it did it again. I was running the AC and noticed the temperature shot up on the gauge. I turned the AC off and within a minute the temperature came back down to normal temperature. Today I noticed when the temperature was high on the gauge I lost power and as I pushed the gas it was a little shaky and lacked power until the temperature dropped back down in to normal temperature.
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Tuesday, July 10th, 2018 AT 12:17 PM
Tiny
STEVE W.
  • EXPERT
As it is not a constant issue I would start looking at the wiring from the sensors and the connectors. If you can get a scan tool that shows live data you could look at the sensor data to see if it shows any other problem when this happens.
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Tuesday, July 10th, 2018 AT 12:31 PM
Tiny
ROBERTBARNES62
  • MEMBER
I plan to look and even replace the temperature sensor. But what would cause the shaky and lack of power? Does this mean it actually overheated?
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Tuesday, July 10th, 2018 AT 12:41 PM
Tiny
ROBERTBARNES62
  • MEMBER
Also, not sure if it matters but it also has a new radiator cap on there too?
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Tuesday, July 10th, 2018 AT 12:52 PM
Tiny
ROBERTBARNES62
  • MEMBER
I found this on another forum and wanted to run this by you to see if this makes sense and if you can tell me if this could also be my problem and how to test to see if this is my problem? Also, in the below passage he says "So if I run without TS, I get no overheats or spew", what does "TS" mean? And can I just bypass that so I can keep running the SUV?

And I understand the wierd overheat now:
Leaking head gasket allows compression vapor into the water jacket. Cold thermostat does not pass the vapor, (The vent in the TS is not big enough to pass all the vapor) so the block fills with vapor and pushes coolant into the (pressurized) reservoir. (So if I run without TS, I get no overheats or spew).

If there is enough coolant, it will push coolant out of the reservior, until the bubble is big enough that it starts bubbling into the bottom of the reservoir. The reservoir is connected directly to the lower radiator hose. Thermostat still closed.

Engine still warming up. Eventually, the hot vapor, or conduction, overheats the temp sender and the head overheat sensor, showing me overheat on the gauge and an alarm light. Coolant is still only warm, but spewing out reservoir, or venting vapor out reservoir.

If I turn the engine off and wait a couple minutes, the TS vent passes enough vapor to flood the jacket with coolant, and the temperature indicator instantly shows normal, and it quits spewing, although still plenty of pressure.

Finally, the TS warms up enough to open, so the bubble goes through the ts to the top of the radiator, stops spewing coolant, and the temperature remains normal.

Continued driving continues to vent vapor through the reservoir cap.
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Tuesday, July 10th, 2018 AT 1:23 PM
Tiny
STEVE W.
  • EXPERT
TS= thermostat. That poster has a bad head gasket and thinks that removing the thermostat is helping, when in reality it is just doing more damage by letting the gasses enter the cooling system. The vent in the TS is also going to let the gas through, it is designed to purge air after all.

If you are worried that it is a head gasket there is an easy test you can do using a test kit.
It is in this guide. https://www.2carpros.com/articles/head-gasket-blown-test
But I do not think you have that as an issue because you say you can turn the AC off and it cools down. A head gasket would just stay hot and it would overheat and steam off coolant.

The lack of power could be caused by actually overheating but it can also be because the ECU thinks it is overheating so it alters the timing and fuel to try to lower the power output and let it cool down, which is why it suddenly runs better as soon as the temperature comes back down.
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Tuesday, July 10th, 2018 AT 3:14 PM
Tiny
ROBERTBARNES62
  • MEMBER
I agree and do not really know what to do at this point. I guess I should replace the temperature sensor and see what happens. Do you think that is what I should do next?
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Tuesday, July 10th, 2018 AT 3:23 PM
Tiny
ROBERTBARNES62
  • MEMBER
Also, should I be checking the coolant temperature sensor or the temperature sending unit or both? I know where the coolant sensor is (behind the alternator), but not sure where the temperature sending unit is located?
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Tuesday, July 10th, 2018 AT 4:33 PM
Tiny
STEVE W.
  • EXPERT
On that engine that may be the only sensor. The other one (if it has it) would be in the intake manifold on the passenger side front. 1999 was the year they stopped using two sensors and started using just the head temperature sensor. But it is dependent on when your vehicle was built. I would check the wiring, also just unplug the sensor and see what you get for warnings. If you get the same hot indicator then you might have found the answer in that a loose connection would act the same way.
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Tuesday, July 10th, 2018 AT 10:21 PM
Tiny
ROBERTBARNES62
  • MEMBER
So I thought I knew where the sensor was, I thought it was behind the alternator besides the thermostat, but I did not see one there. Do you have any idea where it is located?
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Wednesday, July 11th, 2018 AT 3:59 PM
Tiny
STEVE W.
  • EXPERT
It should be in the front corner of the drivers side cylinder head. Tucked up under the intake manifold.
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Wednesday, July 11th, 2018 AT 5:09 PM

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