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Discussion Starter #1
Hello,

A couple days ago I was out for a sunday drive. Everything was going fine and then suddenly I felt like the truck way loosing some power and fighting itself. I look down at the gauge cluster and see that the temp gauge went from being towards the middle of the range down to the bottom of the range.

I pulled over to a gas station expecting the coolant to be gone, but nope, the coolant was a tad low, but nothing terrible. I also squeezed the radiator hose and noticed that there was no water in the upper radiator hose while idling after a 50 mile drive going 70 MPH.

I got the truck back home safely, but the gas mileage was horrific since the truck was acting like it hadn't warmed up.

The next day I replaced the thermostat and thermostat housing and turned the truck on and tried to let it warm up. Before the temp gauge would just sit at the bottom of the range. Now the truck just sat all the way at the bottom of the gauge and wouldn't move what so ever.

I just replaced the temp sensor today with the correct sensor from the ford dealer and now the temp gauge will climb back to the bottom of the temp range and just sit there.

I took the truck out for a drive just to see what would happen and things seem ok but im still loosing quite a bit of fuel. I still have no water in the upper radiator hose. Heater works find and the water pump pulley is turning so I don't think the water pump is bad, but I could be wrong. Im not feeling any excessive heat from the engine bay or any particular part. When I open the coolant cap, water doesn't come rushing out nor are there any air bubbles coming out so I don't think its overheating. Everything including the fluid is definitely hot, so I would think I should be seeing the temp gauge go up higher, but again, I can't be too sure. I scanned the truck for any codes and nothing pops up what so ever. But I had scanned it before replacing the sensor and I would tend to think that a bad sensor should have thrown a code, so who knows if the scan tool is reliable.

Do you guys have any ideas? I don't know what to try next beyond replacing everything and hoping I fix the problem somewhere along the way.
 

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Sounds like you put a 195 degree thermostat into it. When I had a 195 one in mine the needle would only hit the bottom bar of the gauge. It didn't move up to R or M in normal until I put in a 203 degree one.

As for the sensor the PCM does not monitor the coolant temperature so it won't show up on a scan.

You may also have a stuck fan clutch that is keeping air moving through the radiator at all times.
 

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Discussion Starter #4
Is your fan kicking on? On all the time? Could be a water pump issue.
Just got back in from testing things out.

The fan comes on when cold and stays on. I haven't seen it turn off.

Good news is that I found out that if I really kick the gas pedal, the temp gauge will move up a little bit. Bad news is that it stays there and won't come back down.

Im sort of starting to think the water pump is dead.

---------

Its also worth noting that I do have a 203 degree thermostat on the way.
 

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The fan is always spinning because of centrifugal forces, and will not turn off until you turn off the vehicle. That is not the proper way to diagnose a bad fan clutch. Either way, a bad fan clutch shouldn't exhibit these kinds of symptoms either.
 

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If the water pump was doa you would know it from the engine over heating.

The fan will always run with the engine running, however there is a clutch on it that will engage and disengage providing more air flow through the radiator.

If it is locked into the run position it will pull a lot more air. With the engine off you should be able to spin the fan with your hand. If not then it is locked up

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Discussion Starter #7
If the water pump was doa you would know it from the engine over heating.

The fan will always run with the engine running, however there is a clutch on it that will engage and disengage providing more air flow through the radiator.

If it is locked into the run position it will pull a lot more air. With the engine off you should be able to spin the fan with your hand. If not then it is locked up

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I just checked. I am able to move the fan by hand.
 

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My factory temperature gauge doesn't rise very far off the cold end of the gauge unless the engine is working hard; ie, it doesn't range far off the N in NORMAL on the gauge.

Also, the radiator fan turns at all temperatures, but the clutch makes it turn faster when the engine is hot. As noted, you should be able to make the fan blades move by hand when the engine is cold.

This is a post from somebody on some Powerstroke forum a few years ago:

"Comparing the factory coolant temperature gauge readings with those of another temperature instrument, I found the factory's "NORMAL" designated ranges on the factory gauge equate approximately to:

N=190°F
O=200°F
R=210°F
M=220°

"The needle gets off bottom and begins to rise at 150°F.

I spent some time studying all this."
 

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The TSB in this caption doesn't specifically call out the 7.3L clutch, but it describes how a thermal clutch should behave.

(phone app link)


This is from the '97 service manual's cooling system section (implicitly applicable to all F-series engines).
Fan Clutch Test
Spin the fan. A light resistance should be felt. If there is no resistance or very high resistance, the minimum and maximum fan speeds must be checked as follows:
Refer to Fan Clutch Specifications at the end of this section.
Disengaged Fan Clutch Requirement Test — Cold
  1. WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION. Using a suitable marker, mark the water pump pulley (8509), one of the fan blade retaining bolts and the crankshaft pulley (6312).
  2. Connect a tachometer to the engine.
  3. Install a throttle adjusting tool.
  4. Connect a Sun Strobe Light or equivalent. This can be an SLT-1 or SLT-2 Strobotach or an STA-1 Strobe Trigger adapter for the Sun Distributor Test Stand. A Digital Photoelectric Tachometer 055-00108 or equivalent can also be used for this test.
  5. Start the engine and run it at approximately 1500 rpm until engine temperature has normalized.
  6. Adjust the engine to the testing speed in the Specifications at the end of this section.
  7. Operate the strobe light at water pump test speed and aim it at the water pump pulley. Adjust the engine speed until the light flashes and the water pump pulley marks are synchronized.
  8. Aim the timing light at the fan retaining bolts. Adjust the strobe light until it is synchronized with the marked fan retaining bolt (fan appears to stand still).
  9. The fan speed must not be greater than the specified fan test speed at water pump test speed.
  10. Turn the engine OFF.
  11. If the fan speed was greater than the specified fan test speed, check for proper parts usage.If the correct parts are used, replace the fan clutch. If the part(s) are not the correct ones, replace the part(s) and perform the test again.
  12. If the Engaged Fan Clutch Requirement Test is going to be performed, do not remove the tachometer, strobe light or throttle adjusting tool.
  13. If an Engaged Fan Clutch Requirement Test is not going to be performed, remove the tachometer, strobe light and throttle adjusting tool.
Engaged Speed Fan Clutch Requirement Test
  1. WARNING: TO AVOID THE POSSIBILITY OF PERSONAL INJURY OR DAMAGE TO THE VEHICLE, DO NOT OPERATE THE ENGINE WITH THE HOOD OPEN UNTIL THE FAN HAS BEEN FIRST EXAMINED FOR POSSIBLE CRACKS AND SEPARATION. If the Disengaged Fan Clutch Requirement Test was not performed, follow Steps 1 through 5 under Disengaged Speed Fan Clutch Requirement Test.
  2. Block off areas on each side of the radiator in the engine compartment and the front of the radiator grille (8200). This will raise the temperature of the air striking the fan clutch and should cause the fan blade to operate at maximum speed.
  3. Place the air conditioning selector, if so equipped, in the maximum position and the blower switch in the high position.
  4. Adjust the strobe light to water pump test speed.
  5. Start the engine and adjust it until the water pump pulley is synchronized with the strobe light. This will be near the engine testing speed given in Specifications.
  6. Synchronize the timing light with the fan to fan clutch retaining bolt.
  7. The fan speed must meet or exceed the specified minimum fan blade test speed at water pump test speed.
  8. If the fan speed was less than the specified fan test speed, replace the fan clutch.
My truck also rarely shows any significant temperature on the gauge.
 

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Discussion Starter #10
I wanted to return to this thread to give an update.

I had replaced the temp sensor like I said before, and the temp gauge was doing all sorts of funky things. A few days after my last post, the gauge wouldn't come off cold again.

After fiddling with things, the pulleys started to make weird noises, and a day or two later the water pump started to leak.

I had the water pump, belt, and tensioner all replaced along with another new temp sensor. I have been driving it around a couple days and everything seems to be fixed. Not only does the temp gauge behave normally, but the truck runs a lot smoother as well.

If the issue pops back up again, I will continue to update this thread, but for the moment I think the issue is solved. Thank you everyone for your replies.
 

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Discussion Starter #12
Did you look at the old water pump?

(phone app link)
I did not no. I had a shop do it since I am at an apartment and they don't want me working on my vehicles.

Worse yet, I am driving it around today and it seems like the temp sensor might have died again. Truck runs fine compared to last time though, so there has been an improvement, but yeahhhhhhh I think there is a bigger problem. I also now have a lot more smoke coming from the driver side valve cover.
 

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Discussion Starter #13
The problem persists. Gauge wont come off cold again and wont move at all. No water in upper radiator hose after a long drive.

Im not loosing any coolant in the reservoir.

OBD2 still isn't showing any codes.

New Symptom: When I plug in a scanner and let the engine idle, it actually bogs down and will try to stall. Without the OBD2 reader in the port, this doesn't happen.

I also have a pretty big leak coming from the fuel pump now. Im not sure if that has anything to do with the issue though.
 

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The problem persists. Gauge wont come off cold again and wont move at all. No water in upper radiator hose after a long drive.

Im not loosing any coolant in the reservoir.

OBD2 still isn't showing any codes.

New Symptom: When I plug in a scanner and let the engine idle, it actually bogs down and will try to stall. Without the OBD2 reader in the port, this doesn't happen.

I also have a pretty big leak coming from the fuel pump now. Im not sure if that has anything to do with the issue though.
Far as the bog, thats normal with some cheap code readers.
Temp gauge isn't working because there isn't any coolant to read. If it's not leaking externally, and not in the oil, it's going through the engine. (Injector cups are somewhat common)

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Discussion Starter #15
Far as the bog, thats normal with some cheap code readers.
Temp gauge isn't working because there isn't any coolant to read. If it's not leaking externally, and not in the oil, it's going through the engine. (Injector cups are somewhat common)

Sent from my SM-N960U using Tapatalk
The only catch to that theory is that there is in fact coolant right behind the sensor. The moment you crack the bolt on the sensor, water leaks out instantly.

But the potential of a cracked injector cup is on my mind.

After fiddling with it for a few hours I did notice that the stem of the temperature sensor actually wobbles in the housing. My original one and the second one I bought from ford did not do that. I will go replace it again tomorrow to see if maybe I have just been having bad luck with sensors.
 

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If may have coolant on it with the engine off, but running could be a different story.
Is it possible you had a air bubble in the cooling system, which "burped" and made the system low? Or is it repeatedly going low?

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Park the truck level, or slightly nose-down, and fill through one of the heater hoses until it trickles out the heater nipple at the firewall. Then keep filling slowly as you lower the hose to the nipple, and re-connect the hose quickly to minimize the air pocket.

(phone app link)


How old is the t'stat? How many miles/years since you did a really-good coolant flush? Next time, do it with the engine idling so you can see how much coolant the pump is moving.

(phone app link)


At some point, you should pressure-test the coolant system. Each time you find & fix a leak, refill & pressure-test it again longer. This leak was so small, it took several hours of testing to find:

(phone app link)
 
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