As the thread title says, I'm currently having an issue with my 7.3 turbo idi in regard to overheating. Yes, it's over 100 degrees here in Texas- that's a normal summer. But this spring, as soon as the temps began to reach 80 degrees, and starting late last summer, my 7.3 when pulling light loads will begin to run warm. Before going further, I have a Mishimoto aluminum radiator that I've had no issues with thus far, and in years past with the exact same setup and conditions, I've not had this issue.

The issue arose last summer, when pulling a lighter load of maybe 3500lbs of trailer on a typical Texas summer day; however just a few weeks before I pulled loads that were nearer to 7k without issue at speed (70mph). Now, continuing this year, under similar conditions, I'm getting the engine temp light without the temp gauge pegging out, it's still at M or A on the scale. Knowing the factory gauges are worthless; Today, I was able to shoot it with a temp gun and found that I was showing 260ish at the sending unit on the left head, and 190 on the radiator & hoses. So far in the past few months I've replaced the temp sending unit with a NAPA one, the thermostat with another Motorcraft, replaced the fan clutch (Murray from O'reilly's) and I've had the coolant flushed following the thermostat; for the record, the little check ball is now riding around in my cupholder...
The fan I can grab when the truck is off and it has drag whether the engine is cool or warm, there's no difference and I can't distinguish it's fully locking or not. When running, my EGT's show anywhere between 800 to 1100 degrees depending on the topography and it's usually momentary if it gets near to the higher end. Also, my boost PSI hardly ever goes over 5psi... Whenever the truck is by itself and even if I push it hard getting the boost upwards of 7 or 8psi, it doesn't seem to want to overheat until it's pulling a load.

My thoughts are maybe my injector pump is turned up too high, though I haven't touched it in probably four years, however the truck can be pretty smokey when accelerating thru the gears. Or could maybe my oil cooler might be the culprit after seeing the huge difference between it and the radiator upon shooting with a temp gun? However, my oil pressure, even today with the 5k load was consistently around 40psi when at speed though last summer I noticed it going lower when the engine heated up. Or could my water pump be on its way out by not flowing? I haven't seen any leaks. And upon checking my coolant and oil levels, they're perfectly full and as clean as could be.

Any advice or experience with this is appreciated; I looked thru the forums, but no one ever concluded their issue.

 

Seems as though your coolant isn't circulating. This could be caused by a bad water pump (I've seen the impeller break away from the shaft), a bad thermostat, or a clogged cooling system.
First diagnostic step is to remove the thermostat and place it into a pan of water on the stove. Use a thermometer to measure the water temperature. It should start opening at about 195°f and should be completely open by 205°f.
If the thermostat is good, the 2nd diagnostic step is to drain all the coolant, disconnect the lower radiator hose, attach a garden hose to the lower radiator hose and use duct tape to create a seal, and then blast full garden-hose water flow through the engine. You should get a healthy blast of water out of your thermostat housing. If it blows the garden hose off the lower radiator hose, then you have a clogged cooling system.
3nd diagnostic step is to remove the water pump and inspect it for damage, corrosion, mud, broken shaft, etc.

 

Update: After having the radiator flushed at a reputable shop, replacing the water pump with a new one from Napa, exchanging the fan clutch on warranty, and replacing the thermostat with a new motorcraft one that was stove tested, opening at 190 something and fully open by 208; and finding out afterward that the 1st thermostat was actually as good as the 2nd- I'm still experiencing overheating when loaded. Infact, after the new pump and fan clutch, (but not yet the thermostat) the engine temp light came on within 2 miles instead of 50 miles like before! This time though I noticed the audible sound of the fan clutch working.

The good news is that there's still no indication of combustion present in the coolant nor oil or coolant in the oil. Nor does the engine try to get hot when running empty. However, after doing all that, I'm still not seeing much movement in the radiator, even after (carefully) taking the cap off after an easy unloaded run. Even with the upper radiator hose being firm, my thoughts are now that the radiator needs to be replaced as there was some gunk (silicone from a previous water pump job) in the system I could see rattling around and not really flowing in the top tank. The radiator shop even said that it was possible that it would take a new radiator to resolve this.

 

That sounds about right, sounds like you got everything else it could be.. That's gotta be it.

I recently put in a nos international 192* thermostat, it's a rock steady performer, stays perfectly pegged in normal temp range.

Nothing to do, just saying..

I put a used oem 460 rad in about 8 years ago, and have never had it get hot, just needed a hose splicing to get them to mate, 40 bucks at a bone yard and easy to replace if it ever pops, there are plenty of 460 rads out there, just an affordable option that worked for me.

 

Heater ON & full hot ???

 

I've never turned the heater on; both times I've gotten the temp light, I've been able to slow down and turn onto a side road and let it idle.

Today, I talked to the radiator shop that flushed it and was told that they only reverse flowed it from bottom to top. He told me if I brought it back, they would flow it both ways several times with hot water at no charge to me. Being that it's a Mishimoto aluminum 3 row, I am a little worried about the smaller tubes with any residue in the system as opposed to a 2 row with larger tubes, but I guess at no cost other than my time, I might as well give it one more shot before getting another radiator.

 

Personally I would take the time and spend $30 or so for a cheap mechanical temp gauge for the coolant. I had a cheap-o Equus from NAPA that was very accurate and is much more useful than the factory sensors. I did have to drill a hole in the firewall and install a grommet but it was more than worth it to know the actual temperature of the coolant in the block. I have a 2-row aluminum/plastic tank radiator from NAPA and have never managed to get temps over 215-220 loaded uphill in the summer so I would bet there's still a wrinkle in your system. And thermostats should only be Motorcraft or International as far too many people have had problems with the various aftermarket units. For all the hassle of installing a new thermostat its worth paying a few more dollars to get it right the first time--9+yrs on a Motorcraft t-stat in my truck and it relably opens around 188-192 degrees.

Edit: I see you already have the Motorcraft t-stat.

 

Check your injector timing. Is your fuel screw maxed out?

 

I've thought a lot about that... It will roll smoke on acceleration thru the gears and clear up once you level off. I last had it off 4 years ago and the pump was rebuilt and calibrated for a '94 turbo diesel even though mine started life as NA. And it also got new injectors at the time, I don't remember the codes that went in- either way a matched and tested set from a reputable shop. But unless the pump moved on its own somehow over the past year, it should be as it was when rebuilt and reinstalled in 2020. If the calibrations were wrong from the beginning, wouldn't the engine have gotten hot 4 years ago?

I was just thinking of how this all began. Last year in May, I hauled a friend's dead 2005 F250 CCSWB 4x4- 6L (go figure) on my car hauler to a mechanic some 50 miles from home thru some rolling hills maintaining about 65 to 70. I'm guesstimating that I probably had about 9500lbs behind me, the weather was in the 80s and I didn't even come close to overheating, even when I encountered a hill that pushed the EGTs up to 1100 momentarily. Then, in September with hotter weather, I took the same empty trailer to the same town and experienced higher temperatures on the return trip with a very light load.

What makes me lean away from the injection system is that the engine takes a bit to cool down from higher temperatures when idling yet the EGT's will fall back immediately upon deceleration.

 

Do you have one of the laser thermometers? When its hot check the temperature all over the radiator. There should be some gradient from the hot coming in at the top, and cooler leaver at the bottom, but wide variations can indicate clogged tubes.
Flow testing the radiator may indicate if its clogged as well, but I'm not exactly sure how you would set that up, and what the normal flow would be.

 

I have been shooting it with the temp gun. Temps ranged differently all over; the hottest being at the sending unit on the driver's side head. I was able to have the radiator flushed again today and was told they flushed it bi-directionally several times with hot water and that they were able to verify flow was equal on both sides (I don't know exactly how they did that) and that very little came out of it... I've put it back together and ran it solo but haven't put it under load yet- maybe tomorrow. I did observe it idling and didn't see any bubbles even after running it and I also used my combustion leak detector and didn't see anything wrong, hopefully this issue resolves tomorrow...

As of now, it's got a new Napa water pump, replaced fan clutch, verified Motorcraft thermostat, clean & new coolant, and a radiator that's as clean as it "could be"...

 

Update: I ran the truck today some 20 miles today in temperatures around 90 degrees with an empty 5000lbs gooseneck behind me, I was able to run without the temperature warning light coming on. Not that it means anything, but my temp gauge on the dash only made it to "R" in normal while seeing just shy of 1100 on the EGT gauge at the highest for a few seconds while climbing a hill. Barring some slight interference with traffic on some two-lane farm to market roads, I was able to achieve speeds of 70-80mph without overheating and taking two readings, one after the first 8 miles and one at the very end, finding that my thermostat temp was at 195 and my sending unit was at 205 on the highest reading. No, this is not a full load in the Texas heat, but I figure it's hopefully an indicator that my issue has resolved. Also, I opened the radiator cap after returning home and found zero presence of bubbles (no head gasket or crack issues) and for the first time I noticed my coolant swirling as it went down the radiator tubes like water draining. I suppose that a clogged radiator may have been the cause of all of this.