Hello all. I’ve been creeping this forum for the better part of a decade and I’ve finally found myself a problem I can’t find a direct solution to. The truck is a 2005 F-250 with 180K miles. I bought the truck two years ago and it had 140K on it then. I immediately bulletproofed it and had it going for a while on the oil cooler. Deltas rose gradually until I was seeing 30°+. Last weekend, I made several upgrades and along with it I repaired some other miscellaneous problems. I flushed 68 gallons of distilled water through it in total, replaced my oil cooler, lower radiator hose, water pump, swapped to ELC coolant, and installed a new OEM thermostat. The thermostat is labeled 104°C which equates to 219.2°F in the fully open position. My problem with this is that in 100° weather unloaded doing 70 mph on the highway, I’m seeing ECT between 200-215° with my deltas never getting farther than 5-7° apart. I never heard the fan kick on during this but I’ve noticed the fan on my truck usually engages at 220°. Why am I seeing high ECT? Before I flushed coolant, changed oil cooler, new thermostat, water pump, etc. I never saw the ECT over about 200-205°. Could my thermostat I just installed be bad? Could my radiator be plugged? The water pump I put on was excellent quality, belts are tight, everything that I’ve checked has been good. I checked the cold soak temps and they read identical. I know that the ECT I’m seeing now isn’t detrimental to the truck’s health, but when I’m ready to tow my 9K camper here in a couple weeks to the lake, I would like to see my temps loaded at a max of 215-220°. Thanks to all who read and/or reply.

 

My temps in Fla here lately run in same range. 195 ect. 200 to 205 eot running 75 on interstate. My fan runs about 475.
To me that is normal. I have an oem motorcraft 190 degree thermostat. I would first look at your delta's at idle when at operating temps. They should not vary more than 3 to 5 degrees in a perfect world. A little more wont hurt but IMO you start getting 8 to 10 i would start watching a little closer. Now when loaded its a different story your deltas are gonna vary drasticly depending on grade and speed, more than they will unloaded.

 

When idling, my ECT is 188° and my EOT is 190°. I read up on the RT-1169 thermostat and the original thermostat was still in it from 2004, and it was stamped identical to the one I put in which is 104°C. How do you monitor fan speed? I know my fan works because when it kicks on it sounds like a semi, and I’ll see my temps drop fairly quickly. So I don’t think I have a problem there. But under normal conditions in 100° heat, I figured around 200° is where the ECT should be.

 

I run torque pro on a tablet to monitor everything. I have a cup holder mount right there in my console. I use forscan lite and forscan full version on a laptop for diagnostics and dtc's.

 

The current Motorcraft thermostats are not the same as what originally came in our trucks, they perform very differently.

My ect temps run the same...200-205° during the summer.

 

I left out my temps at idle. I run about 192 ect and 194 or 5 eot.

 

So would you recommend the OEM still? I understand that just because they’re stamped the same doesn’t mean they are the same. I’ve read a few threads that people went with the moshimoto, but I’ve never seen feedback from them. I know their radiators are good, but every product is a different ballgame in my opinion. A perfect example of that is Dorman. Their oil coolers are terrible, but their power boards for the FICM are awesome. I can speak from experience on that.

 

The open temp on that thermostat is way high. The Mishimoto 202 thermostat is considered high temp. Something seems fishy with that. Do you have a part number?

What are you using to monitor temps with?

Is that 70mpg highway just cruising, or does it include a bunch of WOT blasts? In 100 degree weather, I'll see 215 ECTs when doing a lot of passing, but they usually come back down to 205 pretty quick.

Not sure why you would expect to be able to hear the fan go on doing 70mph. And it should engage a lot lower than 220. Mine roars at 195 sometimes.

5-7 degree deltas are very respectable, but if you're really that worried about it, try a 190 thermostat and change the coolant temp sensor while you're at it.

 

The thermostat I’m using is RT-1169 which my research suggests it opens at 192°. 219.2° is when it is in the fully open position.

I’m using the Edge Insight CTS2.

I’m cruising at 70 mph on open highway. A few hills here and there but nothing really steep.

I could be mistaken about hearing the fan then. I may have an underlying problem with that that I’m not aware of. I understand that the 7.3 is very different than the 6.0, but when the fan kicks on on my 7.3 it is very noticeable. When I took the fan clutch off last time on this truck, during reinstallment after I tightened it up, the fan took a good amount of force to turn it so I feel confident it is working correctly because the engine and all components were cold.

I’m confident that my deltas are good to go. What brand thermostat would you recommend at 190°? I would like to stick with OEM or a reputable aftermarket brand because I’ve had bad luck with getting NAPA brand thermostats to seal in the past. Why, I don’t know. Just something about their thermostats, because everything else I’ve gotten from there has been very good. I also read on the ECT sensor possibly being bad, but after a good 24 hour cold soak, my EOT and ECT temps read nearly identical to one another. Never farther than 1-2° difference.

Thank you all for the replies.

 

I have 4 failed Motorcraft thermostats, 1 Stant and 1 Gates. With the exception of the original motorcraft, the Stant lasted the longest at 2 years, replacement motorcrafts lasted 1 year and the gates failed after 500 miles. The Stant does the best job at holding temps, 192-194 empty highway and 196-198 pulling the 5th wheel. When they failed, all would begin to run hot and very inconsistant. I'm back running a Stant now and will likely just change it every year, they are cheap and easy to swap out.

 

The only reason I wouldn’t do that is because I hate losing coolant. I would rather have an oil leak than a coolant leak. I know that sounds odd but there’s something about that kind of leak drives me nuts. Did the stant come from advance auto? Have you tried the moshimoto? I’m kind of leaning towards getting a moshimoto after this one goes bad (or I confirm that it has failed). If you clamp the top hose from the radiator, when you remove the thermostat, can coolant back flow up through the block and come out the opening? Or will gravity keep it lower than the port? I know that’s probably a dumb question, but will the pressure up through the lower radiator hose cause back pressure and cause it to spill out? The Peak red ELC I used from my local parts store costs over $20 a gallon. Not cheap. But it’s also “million mile coolant”. Good stuff indeed.

 

You can drain a gallon to a clean bucket and reuse it.

 

The petcock on my radiator is broken off inside the threads. It came like that. It stills seals, but the hex head is gone. Every time I drain and flush, etc, I have to pull the lower radiator hose off. It would be really hard to drain and re-use.

 

No, you don't.

That usually happens because people use the hex to open the petcock, they should have made that a round knurl for hand use only. The petcock is an o-ring seal which does not require torque to seal, and doing so just stresses the top of the part - AT THE HEX.

Often with the top broken off, you can still open the petcock and replace it by using what should be the only way of opening it, an 8mm Allen hex wrench in the middle. Even with a broken hex, there still should be enough meat left to unscrew it.

 

Wow. Now I feel like a dummy. 😅