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Discussion Starter #1
So we made a run from West Yellowstone, MT to Rigby, ID(200ish mile round trip) like we have done several times this winter, but the truck was having random overheating spikes. Going up a hill, I can understand it getting a little warm. But on the flats and cruising at 65 while it's freaking 8 outside is absurd. It got to 219 the first time and then the fan engaged and it dropped the temp like a stone. On the way back, it got to 230 and that's when the fan finally came on. Again, finally it came back down really fast. Several times during this trip it would just start climbing in temp for no reason, stay at 197-199, then drop back down to 177 and stay there for a bunch more miles. Would the thermostats failing cause this?
 

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Possibly. Stuck open, you don't get the temp cycling in the rad. But that's usually a hot weather thing with your temp spikes. In winter, it just never gets to full OP temp and your heater leaves a lot to be desired.

Your ECT and the fan clutch Temp, are two different sources.

You need a good airflow thru all of the coils up front, in order to reach and trigger the fan clutch to lock up. In the hot months, people towing will see the spikes, then eventually the fan locks up and the ECT plummets.
Recommendation; open up the cooling stack and clean the debris buildup between each coil. With a good airflow, the fan will do a partial engage most times, and you'll never hear a full lock howl.

But seeing it @ 8* out....I'm wondering if you might have a failing water pump.
 

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Discussion Starter #3
The truck has 213k on it so it is possible that the pump is taking a crap. I will have to check the PO's service records and see if a pump was ever done. We have the winter front on currently but that shouldn't be causing the spikes like that. It should just stay at one temp and stay there unless under load. Mishimoto thermostats are going to be on order in the very near future. The trans temp also rises with the coolant temp. I'm guessing because the trans fluid circuit goes through the radiator as well as the frontal cooler. The pump isn't weeping, but then again, I did flush what looked like mud and two different types of coolant out of the truck when I did the injectors.
 

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Trans fluid flowing thru the rad, temps mimic the ECT.

Mud is not good.
Still a mystery why people don't trust Dex and stick with it, instead of trying to go green which has a far less lifespan. Where's the gain?

Weep hole check, it's possible to have an internal shaft fail and not leak, and also not turn the gear driven pump.

I wouldn't spend extra $, a set of inexpensive Stants from rock, work just the same.
But again, stuck open T-stats in cold weather, it just never warms up and you have no heater.

But no coolant flow from no pump action....shouldn't have the Trans temps spiking.
It's a mystery.
 

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Like Hook'em said, being in temps that cold with an overheating issue is unusual. Thermostats are a good place to start and see if that does cure it. That's a lot easier than a water pump replacement to start with, at the very least. You said you flushed 'mud' out when you did injectors- would it be possible that there is a blockage floating around somewhere that could contribute to this as well... but you'd also think that it would get caught at the thermostat or something and be visible when you crack the t-stat housing off there... But, a pump issue could be too... keep us updated!
 

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Discussion Starter #6
Update: I didn't have time to get the thermostats done myself so my wife paid a mechanic friend of ours(yes, he's reputable and is the only one that my wife will let work on her truck besides me) change them for us. The truck on about a 10 mile one way run slowly gets up to temp. Hits 197 and falls back to 180ish then repeats the process until it finally settles at about 188-192. I also did a 0-90 pull and it only went from 185 up to 197 and then went right back down. The stock gauge on the cluster is garbage. It starts coming up indicating hotter than 160 but it is only actually 105. We haven't taken it on any long excursions yet. As for a chunk of mud breaking loose, there might have been one on/near the block heater that dislodged due to daily use now that we live in Montana. I did the initial week long flushing session in June of 2018 and then drove it across the country three times, before settling in Montana. I'll update if anything else changes after this weekend's excursion.
 
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