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Newbie here. First post.

I go out to start my truck in the AM, let it run until EOT and ECT are both at LEAST above 150. However, it doesn't matter how warm it gets, it won't blow heat in the cab. Ice cold air only. Until I put it in drive then bam, blows heat like normal (maybe even hotter than normal). Once the truck is thoroughly warmed up (20-25 miles of highway driving), ECT sits around 196 but EOT will go anywhere from 150 to 210 in a matter of 1-3 minutes. Then back down then back up, etc etc. It seems to have no rhyme or reason as to what the EOT is. ECT stays mostly around 196 but every now and then it will drop down 15-20 degrees but it usually comes back up pretty quickly. Then if I find myself stuck in traffic (which is a lot here in ATL), before I even come to a complete stop, I see the ECT steadily climbing above 200. If it's an absolute standstill traffic jam, it will hit 220. I imagine it would continue to climb but that's the hottest I've let it get before shutting it down. When it begins overheating in the conditions I've just described, the EOT climbs steadily with the ECT. This is the only situation that they seem to rise and fall in accordance with each other. Otherwise, there's generally not much of a correlation between the two temps. And once it begins to overheat, it is very difficult to get either temp below 200 regardless of weather or driving conditions.

I've tried "burping" the cooling system to clear any air that might be in there--- still starts overheating even with the degas cap off. The seals on my EGR Valve need to be replaced which I will do today. Radiator was replaced less than 10k miles ago. Based on the research I've done over the last couple of weeks, I'm guessing bad water pump impeller (possibly entire pump failure?) or a bad thermostat. Only thing is, of all the threads I've read.... I haven't found anyone that's having exactly the same issue as me. Some are very similar but none identical. I just don't want to keep replacing things that may or may not need replacing just to wind up having to take it to the shop in the end. Trying to save money by doing it myself but it's counterproductive if I don't know exactly what's wrong with it.

2005 F-250 Crew Cab King Ranch, 257,xxx miles, 4" turbo back, EGR delete, ARP studs, blue spring, upgraded oil cooler, AFE intake, coolant filtration system (Cat ELC coolant), Rotella T-6 every 5k miles, fuel filters every 15k miles, diesel kleen probably every 2-3 tanks.


Thanks in advance for any insight/help/suggestions!
 

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For the heat, I'd check the actuator above oil fill port. Sounds like you might have a vacuum leak there.

For the high temperatures, is the engine fan running? Maybe check the clutch/relay/fuse?
 

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we are a little late to the party

if he had a vacuum leak there it wouldn't affect that "actuator" heat wise

that is just a valve that closes when vacuum is applied ( max AC ) to keep the hot water from circulating thru the heater core

the heat working with the RPMS also rules that out as a heat loss source

would be checking tstat / coolant psi/ water pump circulation/and fan
 

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I'd look at the water pump. Maybe the impeller has come apart and only pushes 50% of what it's designed to at lower rpm's. Pretty easy to replace too (couple hours for you first time), and not a bad idea considering your mileage

 

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Check your radiator cap. Is it the small spring? Ford cap with the small spring will fail and caus overheating. If the dealer replaced your radiator they likely replaced the cap with a Ford cap. The Gates cap has larger improved spring.
 
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