deisel fuel in radiator

[lonewolf]

Hello and thank you for the opportunity to be a part of this forum rawze. I have been reading and learning a lot of info so far just read as a guest and im hopeful that as a member I can finally get some answers for some issues I am having with my truck. I have a 2006 kenworth w900l with a cummins isx cm870 in it. Set at 600hp 1850ft lbs torque. 18 speed trans, 3:36 rears, low pro 22.5 tires. Fuel milage is about 4.5 - 5.5mpg at 70mph empty. Truck has not been demandated. However I am a power only hauler so even when im loaded im empty 70% of the time. The best mpg I have seen is in northern half of the country. The worst is southern half coast to coast. When temp out of side gets over 70° motor starts to warm up excessively and power and performance fall right off. Millage is the same loaded or bobtail. I bought this truck almost a year ago and it had about 250000 miles on overhaul. Since I've had it I've had to replace #5 injector, egr cooler replaced cuz it was cracked, and I've had overhead reset twice. Trying to figure out what is wrong with this thing because I know it should be performing a WHOLE lot better than it is. I blew a steer tire at speed limit on I-70 east of Denver a month ago and in my down time I've been applying some of the stuff I have been reading about here. So that when repairs are done ican see if it helped any. Which brings me to my first question. While doing the egr tune up last night I found what appears to be diesel fuel in the radiator and not sure where it came from or how long it has been there. The only time radiator has been drained since I have owned it was when egr cooler was replaced. I have never had to add fluid to system and it has never left a trail or a puddle from overflow. The only time any fluid has ever came out of system was when I had blow out then it spewed from overflow tube till radiator cooled off and new steer tire was installed. Radiator was checked in Denver when repairs were made to get truck home. Hasn't made a mark since. Guess I am looking for any help figuring out how the diesel fuel could have gotten in the system with out ever over filling it. Like I said earlier the truck has been down for a month getting repairs from tire damage and almost finished. When finished this thing needs to recover from down time. Flushed system with water at opperating temp last night for an hour or so and going to get stuff to flush today to see if I can clean system any better. So question 1 if diesel fuel is in the radiator that could cause it to run hot correct. Question 2 is it possible to miss diesel fuel in fluid when the shop that did egr cooler refilled the radiator. Truck has run like this consistently since I bought it and any help would be greatly appreciated. Sorry for the long post but felt the more info I gave the better the responses would be. Thanks again in advance.