[jdkskyking]

Test Drive... Success!! 

Bentonville Arkansas to Neosho Missouri via I-49 and return. 
OAT 75*
Route has several grades that test the engine and cooling system. 

After the engine warmed up the coolant temp was steady at 190* plus or minus 5*. The temperature remained constant pulling the grades at 75 mph. 
It would appear that I resolved the fluctuating coolant temperature issue. 

A related issue I experienced while climbing the mountains in Colorado was high coolant temperature. Of course we suspect the radiator and hydraulic fan system. I thoroughly cleaned the radiator and have replaced components of the hydraulic manifold. I’ve got a new fan solenoid on order. 

So, has the radiator and fan been wrongly accused? Possibly so but they’re still suspect. 

The thermostat I removed from the engine is not a Caterpillar part. When I removed it from the housing I  gave it a quick look and set it aside. I was focused on putting things back together, flushing the system, and get it back on the road. The boss wanted to get away for the weekend... 

If you’ve never “serviced” your coolant system I can tell you this. You have lots of time to think about the situation. I ran the engine for an hour and a half with the Cat cleaner and distilled water. Then I flushed the system in a similar manner. During my test drive it finally occurred to me that my problem could be a thermostat that randomly sticks. Sticks open, closed, half way, and maybe even works normally...sometimes... 

I took another look at the old thermostat. I’m certainly not a forensic mechanic, if that even exists, but I’m fairly certain the galling and unusual wear patterns on the thermostat may substantiate my new suspicions.

           

What I do know know is I have a engine that behaves like it was designed to do, has a relatively clean radiator and engine block, and updated parts. 

My takeaways... 
Clean the radiator often. The road is a nasty place. Don’t just hose it out, spend an afternoon with it. 
Verify how old your coolant is. If you’re not sure change it but thoroughly flush the system and don’t forget about the dash heater system and preheat system. 
Caterpillar recommends changing the thermostat on a regular basis. I was told every five years would be a good idea. 
Obviously monitor your engine parameters and track trends and changes.  
Keep a log book of things you notice and do to your rig. 
Only use genuine manufacturer replacement parts. Yes I add aftermarket items but on some things, Cat in this case, it pays to go with the original. 
Plan your repair, replace or fix time limited items as long as you’re at it. In my case, I had a limited time frame. I would have liked to replace other items such as the silicone coolant hoses. You’ll probably need to order parts and some may take a while to come in. 

Working on your rig yourself is rewarding and can be frustrating. If you are confident and competent you’ll end up with a job well done and no doubt you got what you wanted. Another few perks, you get to know your rig intimately and can upgrade parts or systems. You may also stumble across another issue or problem you can also correct or get out ahead of. On this project I found a oil leak that I hope will be corrected by simply tightening a few bolts. We’ll see...

What else.... 
As I mentioned, my “header tank” had scale buildup and rust in it. I’ll replace it with a new stainless steal or aluminum tank. I also found out that the coolant sensor needs to be relocated below the level of the sight gauge, a change that came on later Cat 15 models. Might even add a recovery tank. 
Replace the radiator someday when my pockets are full of money. Yes it will likely need to be done. 


A big thank you to everyone that has helped me with this journey. I certainly hope my findings may help someone else recognize or solve a issue they have. I’m happy to answer any questions and will post a few more pictures of the work I did. 

Take care!
JK