2002 7.3 overheating
Cargo Master
Joined: Jan 2016
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Some ideas..
If overheating sitting still might be something with the fan. If overheating at high way speed could be something as silly as a clogged air filter.
When engine is at operating temp, see if top radiator hose is warm/hot...might just be an air pocket since you recently drained the coolant.
If overheating sitting still might be something with the fan. If overheating at high way speed could be something as silly as a clogged air filter.
When engine is at operating temp, see if top radiator hose is warm/hot...might just be an air pocket since you recently drained the coolant.
Hotshot
Joined: Jan 2010
Posts: 10,060
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From: Bristol, TN.
Possibly dirty radiator fins so air flow is reduced. At highway speeds, I would expect fan clutch to play little if any role if air flow through radiator is not blocked. Is your truck actually overheating i.e how do you know? Just asking, not a put down. 
Steve
Steve
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Cross-Country
Joined: Aug 2003
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Yes. I've checked everything. It runs normal (needle dead center) until I start increasing speed. Then the Guage starts climbing. .Top hose very hot and lower one not much cooler but if I stop and keep engine running, the temp comes back to normal in maybe 30 seconds. Is it possible the thermostat might not be opening all the way? When I changed out the antifreeze, all looked clean. No particles in it.. I didn't do a chemical flush but flushed till water was clear. Could this be a lower radiator hose collapsing? It's very soft. I believe it's a Delco hose.
Cargo Master
Joined: Jan 2016
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That's a real good point...always a good idea to verify your engine is actually overheating and not just a faulty sensor.
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Cross-Country
Joined: Aug 2003
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I used the stock Motorcraft replacement with the built in gasket. I checked the other day when we did the fan clutch and it is installed properly. Radiator, AC condenser and intercooler were clean
I also reverse cleaned them. Good air flow coming through. Heater good and hot when turned on high.. Don't have resistance values on the temp sensor but would like to check that too. Plan to pull the new thermostat and test it out of the engine. I believe it's a 195 degree thermostat.
I also reverse cleaned them. Good air flow coming through. Heater good and hot when turned on high.. Don't have resistance values on the temp sensor but would like to check that too. Plan to pull the new thermostat and test it out of the engine. I believe it's a 195 degree thermostat.
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Hotshot
Joined: Jan 2010
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From: Bristol, TN.
Let me ask you this. Is the current situation a change for your truck from its past operation? How did you decide to do the most recent work on the cooling system?
Steve
Steve
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Postmaster
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From: Colorado Springs
Are you using the idiot gauge in the cluster or actually taking temps using a IR Thermometer or using an aftermarket gauge?
Coolant sensor plug tight?
After the flush did you park the truck nose up and let it idle with the degas bottle cap off to let the air escape?
Are you seeing air in the degas bottle?
How old is the cap?
Is the cap OEM or Aftermarket? Aftermarket caps have had issues sealing.
‘Did you replace the thermostat housing, stock or Billet?
Fan put on clutch correctly? I don’t know if it can be put on backwards but it happened to a buddy with his Jeep.
These trucks have a very robust cooling system overheating is rarely an issue. I would check the thermostat housing with a IR thermometer before and after the thermostat.
Coolant sensor plug tight?
After the flush did you park the truck nose up and let it idle with the degas bottle cap off to let the air escape?
Are you seeing air in the degas bottle?
How old is the cap?
Is the cap OEM or Aftermarket? Aftermarket caps have had issues sealing.
‘Did you replace the thermostat housing, stock or Billet?
Fan put on clutch correctly? I don’t know if it can be put on backwards but it happened to a buddy with his Jeep.
These trucks have a very robust cooling system overheating is rarely an issue. I would check the thermostat housing with a IR thermometer before and after the thermostat.
Logistics Pro
Joined: Jan 2010
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Did you add the special diesel additive to the coolant when you changed it? I don't know if it's necessary in the 7.3 but I had a 6.0 that would run hot until I added a bit of that additive from Ford, and the problem went away as soon as the stuff cycled through the system.
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Cross-Country
Joined: Aug 2003
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Steve, I don't know how long it's been a problem as I hadn't had the truck up to highway speeds for two years. I did the antifreeze change because it was due. Replaced the thermostat, housing (stock), hoses. Used NAPA long life antifreeze that they said was proper for my engine and also put a bottle of Ford, anticavitation fluid in. Plenty of flow from the bias inlet into the degas bottle. No bubbles. Original cap. Holds pressure just fine. Haven't checked yet with I thermo. Need a hot day and have to get it up to 70mph for a distance to get it to overheat. I would sure love to find the specs for the temp sending unit as to resistance values. I measured it and was around 30 ohms when cold and over 2K ohms at normal operating temp as indicated on the dash gauge.
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
Steve, I don't know how long it's been a problem as I hadn't had the truck up to highway speeds for two years. I did the antifreeze change because it was due. Replaced the thermostat, housing (stock), hoses. Used NAPA long life antifreeze that they said was proper for my engine and also put a bottle of Ford, anticavitation fluid in. Plenty of flow from the bias inlet into the degas bottle. No bubbles. Original cap. Holds pressure just fine. Haven't checked yet with I thermo. Need a hot day and have to get it up to 70mph for a distance to get it to overheat. I would sure love to find the specs for the temp sending unit as to resistance values. I measured it and was around 30 ohms when cold and over 2K ohms at normal operating temp as indicated on the dash gauge.
Here's is my thinking and be warned I am a fanatic about diagnosis. So far all you have is a gage reading. You do not actually have evidence your truck is overheating. I am not saying ignore your gage, but you have to have something more concrete. I am sure you have considered this. Now as to resistance reading, I don't know yours, but in my work on RVs I learned to look only for extremes, basically "OL" or "0" on my Fluke. I learned too many folks were replacing parts based on readings being a little off normal so I never went simply by my meter, although it was my most often used tool.
Here is a second thought. On my 02 7.3 the fan clutch virtually never engaged other than perhaps towing and pulling a heck of a grade. You just replaced it so assuming it good, do you hear your fan? That darn thing sounds like a helicopter is about to land, it is no way subtle. When you gage goes up, do you hear your fan engaging as that would be a second device signaling heat is building up. If you don't hear it, I would be more skeptical your truck is overheating and be more focused on a problem with your sender or your gage.
Good luck,
Steve
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Cross-Country
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Ok, through process of elimination, I pulled the thermostat. Put it in a pot and raised the temp to roughly 210 degrees. The thermo is listed as 192 degrees. Now I realize this thermo is 2 stage. Looking at it in the correct orientation when the temp climbed up past 190, it started to open. At 210 it was open approximately 1/4 inch. The metal disc on the bottom of it to the bottom of the triangle portion that the slug goes through was 7/8 inch and when hot was 1 1/4 inch.. Does this sound normal? If so, I'm trying to figure out how to attach a mechanical gauge to test it. Would that plug just below the the thermo housing be a place to puthe one in there or does anyone have another suggestion. The fan did not come on when it read hot and that was why I replaced the clutch thinking it wasn't working. The new one didn't either so something else is going on. The fact it reads normal when under 60mph and when temps outside are cool even at 75 it stays in the normal reading so either the sending unit is out of spec or there is some sort of restriction in the cooling system. When I changed the antifreeze, the stuff came out clean and looking down in the pump through the thermostat mount, there is no scale or anything but a slight discoloration.
Hotshot
Joined: Jan 2010
Posts: 10,060
Likes: 491
From: Bristol, TN.
Sounds to me like you have two fan clutches that either don't work or didn't come on because extra cooling was no required as the engine was not overheating. What's the probability of two bad fan clutches. I bet just about zero.
Steve
Steve
