Overheating

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.

Okay, how do I check to see if the fan clutch is bad?

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.

Thank you so much. I just ordered a new fan clutch and will install it soon. Thank you

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

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!

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.

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.

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.

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.

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.

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?

Also, not sure if it matters but it also has a new radiator cap on there too?

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.

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.

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?

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?

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.

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?

It should be in the front corner of the drivers side cylinder head. Tucked up under the intake manifold.

So I will have to take the intake out to get to it? Or can I get to it by just taking the alternator out?

You can see it without taking anything out, depending on what tools you have you may be able to remove it without taking the alternator out as well.
There are a couple YouTube videos that show the sensor and its removal.

Okay, so I think its the thermostat that is bad. Even though it is brand new I think it fails from time to time. Last night, 2:00 am, I found out that it did not open and caused the SUV to overheat. I limped it to the nearest gas station where I did not have any tools to take the thermostat out, but what I did do what remove the upper hose and tapped the thermostat with a screwdriver and then filled up with water and it opened and ran good. My question now is, what can be making the thermostats to fail? I put a new one in about three or four months ago, once it failed I put another one in on the 4th of July and now it has failed. Any idea why they are failing? Do you suggest any brand or type I should get now? Right now it has a Carquest from Advance Auto Parts.

Did it actually boil over this time? Brand wise I use OEM on repairs as the aftermarket parts can be a real headache anymore.

Yes sir. It boiled over and the top radiator hose was not flowing with coolant. After using the screwdriver, to tap the thermostat with the upper hose removed, it opened and once everything was put back together it ran great and the upper radiator hose was flowing with coolant. I am trying to see what is causing these thermostats to fail? I guess I will swing by the fire dealership and buy an OEM part to replace the aftermarket one that is in there.

I have had a bunch of aftermarket thermostats test bad out of the box over the past few years. Even the "good" ones like Robertshaw, Stant and Gates. These days I buy OEM, then test it before it is installed.

So now I am wondering if the sending unit is good and the thermostat was delayed in opening. Maybe it was getting hot and before it boiled over the thermostat opened. I guess I will know once I buy a new one. I will keep you posted as to if this fixes the problem.

Replaced with Ford thermostat and it overheated, boiled over. Looked for sensor but cannot find it. Looked on the driver side in the intake manifold as you suggested but there is not one in there. There is a sensor of some type on the front of the engine towards the right on the front. Also, for the time being to get me home, I took the thermostat out and drove home. It did not overheat at all then. I know I do not need to drive too much like that, so do you happen to know of another location the sensor is? Could the one in the front of the engine be the correct one?

The sensor will be in the corner of the cylinder head inline with the back of the alternator. However, as it is actually boiling over the sensor is not the issue. You have an issue with either the coolant not circulating (water pump) or the radiator itself is partially blocked.
The sensor only tells the computer the engine temperature so it can calculate fuel flows and display the temperature.

How long does it take from a cold start to heat up and boil over? Removing the thermostat if it has a bad water pump would make it act like a thermo-syphon cooling system. I do not think you mentioned checking or replacing that? But if pulling the thermostat out actually let it run cooler I would pull the pump. Some have a plastic impeller that cracks and then spins loose.

I found another a video showing where the sensor is. So thank you for that even though now you do not think that is the problem since it is boiling over.

About four or five months ago I replaced the intake manifold gaskets, water pump, thermostat and I also flushed the cooling system as well.

I was having a problem with not getting any heat in the SUV. I was told it could be a bad heater core or air getting in the coolant system causing air pockets. I saw that my intake manifold was leaking coolant so I knew the gaskets needed to be replaced. After I replaced all of that the SUV started to overheat. I then replaced the fan clutch and thermostat. It still was over heating. I then replaced the thermostat again thinking I just got a bad one. It ran good for about a day or two and then over heated again. Just the other day I put a new thermostat from ford in there and it still over heated. I removed the thermostat and the truck does not overheat now.

So new intake manifold gaskets, new thermostats (only lasting for about two days each before failing), new water pump, new fan clutch. but it still overheats.

Could it be a stopped up heater core? A stopped up radiator? If either of them were stopped up would removing the thermostat allow the SUV to run cool?

Also, let me say when it overheats it does boil over and the top radiator hose is empty. Now that I have removed the thermostat the upper hose stays filled with coolant and the truck does not overheat.

I know there has to be a problem but I just do not know what to do next.

This did not start until after you replaced the intake gaskets correct? Then it started overheating. I wonder if you got the wrong water pump or a bad one. Do you have the box or part number? If the pump impeller was wrong it would try to pump coolant backwards. The thermostat would not open correctly and it would overheat.
A plugged radiator should act the same way with or without a thermostat if it is blocking water flow.

I replaced my water pump with one from Advance Auto Parts, part number T4203. I compared the new to the old and visually everything looked the same as far as impeller and size and bolt pattern. Is there anyway to test it?

That should be the correct one. Did you replace the cap as well? A cap that will not hold pressure could cause it to overheat as well? Just trying to figure out what changed from pre-gasket low heat to post gasket and overheating.

I changed the cap around the same time too. I know this is so crazy to me and it is really becoming a headache, but I have to figure it out so I can put another thermostat in there and it run right. To me it just seems like the thermostats are working for about a day or two and then they stop working or start working off and on. For me to go through three or four over this time frame is just crazy.

I do not think the thermostat itself is the failure. They will not just stop working like that. You said you had no heat. The system flows water through the heater core as a bypass during the time it takes to warm up. That is what the disc on the thermostat does, it closes that port once the coolant gets up to temperature. If the heater core was blocked there would be very little coolant flow and it would heat up faster, but it may heat up too fast.

If you can it might be a good idea to flush the system to check if coolant can flow through the engine and heater core. You should be able to disconnect the hoses that go to the core and flush it with water. If nothing flows through then it is blocked. You could also try just connecting a hose to bypass the heater core and see if it runs cooler or hotter.

I am betting it is something that is just being overlooked.

So to make sure we are on the same page. I need to flush the system to ensure I have good flow. I can also bypass the heater core and then run the engine with thermostat in to see if it overheats. If I bypass the heater core and all works well then I know I need to replace the heater core, but if it still over heats then the heater core is not the problem, correct?

Do you by chance know the heater hose size so I can buy a coupler to bypass the heater core?

You are correct. They use a quick connect Believe it is 5/8" But for testing just stuff a hose on and use a clamp to hold it in place. If the flush seems to flow okay through the core it likely is not plugged.

Okay, I will try it and let you know what happens.

Sorry it took so long to get back, but been super busy. So the latest is I bypassed the heater cores and installed a new thermostat. It seems not to overheat but now it seems to have a very small stutter when hitting the gas. I was thinking maybe new plugs would fix the problem but haven't tried it. But what caught my eye during the test drive is that when I got up to around 60 mph the service engine light started to flash. What does that mean?