Long time lurker and first post so go easy on me please!

I picked up an 04 f250 with 140k miles about a year ago that had just been studded and a new oil cooler from what I was told was a "reputable diesel mechanic." I was given receipts for the work done at the purchase. I brought a bluetooth obd reader and monitored EOT/ECT delta on a test drive and everything looked good at 65mph (<10 degree delta) and drove it worry-free for the first few months. I had basic understanding of common issues prior to purchase so it seemed like a good deal. After the first 5000 miles of watching temps, deltas were on the rise so I picked up and SCT tuner from gearhead with tunes (never uploaded) and switched to the scanner to verify the readings weren't wonky from the cheap obd/app combo. Watched deltas climb to 20 degrees and decided to do some work. Decided coolant flush, Rotella ELC coolant, OEM oil cooler replacement, welded egr delete, IPR coolant filter/manifold, and odds and ends like thermostat, turbo drain line, radiator/degas hoses, and blue spring kit. This is my first real wrenching project but I did a good bit of homework prior and went OEM with everything save the IPR coolant filter setup.

My flush procedure was maybe not as thorough as some would like as I had issues with my availability to do the work with surprise visits from family and could not hunt down Restore/Restore+ in time so I had to make due with what I could get my hands on in the moment. I replaced the engine drain plugs with fumoto valves and did a couple of the dieseltech ron garden hose flushes followed by just under a gallon of simple green and about 6 flushes with distilled water until it came out clear. I did not pull the thermostat as mine is the model with the EPB sensor (pretty sure that's what it is) that is mounted to the thermostat housing and had no clearances to reach the bolts without removing the fuel lines in the way. During each flush, I ran the truck for about a half hour to get it to operating temp to try and get the water to cycle the whole engine. I replaced the thermostat later during the oil cooler swap and in hindsight would have pulled the thermostat for the flush because it wasn't AS difficult to get to as I originally thought.

As a whole, the oil cooler replacement went well. I am fairly confident that I kept all debris out of the intake and oil cooler cavity (thanks Ron) and got everything back together as it came apart. New seals and orings all around. Found an intake manifold bolt and a bolt for the oil cooler housing that were never tightened down by the previous mechanic. The IPR manifold for the coolant filter made it a real struggle to get the turbo back in, but when I finally got it in, no exhaust leaks! I had a local welder cut some stainless and weld up my EGR and he did an awesome job.

During my flushing, my deltas climbed up to 30+ degrees and made it increasingly difficult to get my coolant temps up to operating temp. After the oil cooler swap my coolant temps now shoot up to 199 and then settle back down to 192-194 on the highway. Oil temps have climbed to 208 at the highest and I am now seeing a 12-15 degree delta on extended drives at 65 mph (ambient temps 75-80 degrees). That delta is consistent from the first drive after the oil cooler swap to now about 3 weeks later. Obviously it is concerning, but it's a step in the right direction, and aside from the delta, the truck is running great. I've pulled the coolant filter and confirmed that it's not clogged and double checked coolant levels to make sure it's topped off.

All that being said, after a cold soak, my EOT is consistently 3-5 degrees higher than ECT and trans fluid temp (ECT and Trans always within a degree of each other). This is every morning when I start the truck up, without fail. I am hoping that my EOT sensor is just out of spec and giving me a higher temp reading, but I don't know if that offset would be consistent at higher temps. Is there a way that I can test the accuracy of the sensor further to rule out bigger issues? If it comes to replacing it, can I replace it without pulling the oil cooler housing? My biggest fear is that my EGR was on it's way out before I had it welded and maybe I have restricted coolant flow. My truck never exhibited any signs of a failing EGR that I am aware of. Never any white smoke and never any coolant loss. Like I stated previously, I don't have much experience in this regard so I am totally open for suggestions. Please and thank you for any advice you may have!

 

I'd replace the sensor.

You shouldn't have to pull the oil cooler housing.

 

Wow, great job doing your research before doing the job and executing it properly. Sorry to see your deltas are still high. I would start with the EOT sensor. I don't know if your 3F variance stays consistent to higher temps, but it's worth and try. Should be able to access it wtihout removing anything but the electrical connector on top.

How much debris are you getting in your coolant filter? I always recommend running the coolant filter for a few weeks before doing the oil cooler as that will help clean the system up.

 

​​​​​​​Awesome, just found some other posts confirming that it's a pretty easy swap. Just don't want to fight the turbo again if i don't need to!

 

Thanks, I only wish I would have planned a tiny bit better and gotten the right flush chemicals and done the coolant filter first. Idk how i could have installed the manifold without pulling the turbo like IPR advertises though, but I guess it's possible for someone with infinite patience and baby hands. I could have set it up as a bypass first and converted to the manifold after the cooler swap but I wasn't that forward thinking. I will pull the coolant filter tonight and check again, but when I first pulled it, it was just a moderate bit of rust. Assumably from having it torn down for just under a week while I was working on it and straight distilled water in the block for that time. I'll begin shopping a new sensor in the meantime.

 

ECT and EOT sensors are quite literally identical sensors on these engines. If you suspect an issue with the sensor itself, you could easily swap the sensors around to see if the issue follows the swapped part. That'll tell you very quickly if the sensor itself is faulty, or if you need to dig further.