Help! My truck is using diesel as a coolant! + other problems...

Hello all. I’m having a problem and I was hoping that within the circumstances of my situation you all could provide some sound advice to get me by. I’m sorry in advance for the long post here but I’m going to try to be as detailed as possible so that if there is some seemingly pointless detail that might be crucial it’ll be included. First off my truck is an old JB Hunt truck 2004 Freightliner Century with a 12.7 Series 60 DDEC V w/EGR with about 840k miles. About 3 months ago I had to replace my ecm due to a cracked ecm housing so I bought a tweeked ecm that supposedly had bumped MPG, 550hp/1850lb-tq with an EGR-fix. My egr use to occasionally vent and I would loose power for a second or two midrange. The tweaked ecm fixed that as well as boosted hp/tq some but did nothing for my MPG. About a month ago I started to loose power, more noticeably on big hills. Then while offloading I noticed my coolant overflow tube squirting a good amount on the ground. The coolant reservoir was full to the top and the coolant smelled like diesel. I was getting a coolant reservoir low level warning code and engine shutdown. I replaced the sensor but it was still triggering a low level/shut down. I’m thinking the sensor was fine but its designed to measure “coolant” not diesel so thats what made it think the reservoir was empty. Though I haven’t tested this theory yet by plugging in back and submerging the sensor in coolant. I ended up bypassing the reservoir level sensor by unplugging it. The diesel level in my Davco fuel filter/water separator cup was high and murky. After the truck sat overnight the engine would start right up fine but would start to chug and want to die blowing out some white smoke out the stack for about a minute then it would idle normally. Mechanic said my injector cups are bad and need to be changed. He does not think my tweeked ecm may have caused my problem. What do you think? It seems like whats happening is the fuel injector coolant tubes are getting diesel thru the injector cup seals while the truck is on and the fuel rail is pressurized. But when the truck is turned off with no pressure in the fuel system then hot pressurized coolant seeps into the fuel rail. That would explain why the initial fuel in the injector starts the truck fine but then the seeped coolant contaminated fuel makes the engine chug and want to turn off until the fuel pump clears the coolant out of the fuel rail and pushes the remaining seeped coolant/fuel into my fuel tanks via the fuel return line and then makes my Davco cup clogged and murky. Mechanic says that the injector cups are the newer screw in stainless DDEC V ones which means the head does NOT need to come out to change them out but mechanic also recommends doing the head gasket at the same time, just in case. What do you think? However I had no white frothy stuff in my oil and although there was some slight murkiness on the bottom of my coolant reservoir tank there was no clear signs of oil in my coolant. I’ve seen mechanics use diesel as a good cleaning agent so this slight murkiness might be the diesel power cleaning the internals of my coolant system. Your thought on this? I did notice some fresh oil stains coming from the oil dipstick tube but no significant loss of oil I could measure on the dipstick. Maybe a bad o-ring on the dipstick or worst case some premature ring wear and I’m getting blowby? Could some possible slight fuel starvation caused this? Also since the full to the brim reservoir level does not get fluid sucked back into the cooling system after cool down. My guess is this indicates that it is in fact diesel replacing the coolant completely and not gasses passing thru the head gasket pushing fluid out the system. Your thoughts? Mechanic said the whole job is gonna be about $4000 and if the coolant damaged my injectors I’ll need to tack on another $3000. He also said that once the head is off he’ll inspect the piston sleeve liners and see if Its time for inframe which just about gave me a heart attack when he said how $much $more that would cost. Well since I’m just about broke right now due to an unforeseen substantial expense I had recently, I had no choice but to cross my fingers and run more loads like this and make the money to pay for this repair. Mechanic didn’t think it was a good idea but understood my situation and said I would have to change out every bit of coolant rubber that came in contact with diesel, front and rear cab heater hoses and including possibly the water pump, and watch for any coolant hose failures. Anything else you can think of on this? So I changed out the fuel/water separator filter, did an oil change and so far have run about 3800 miles on it like this. To keep the diesel clean and try to save my injectors I have not turned off the engine since and its been running pretty clean in the Davco cup for the most part. I only had to change the filter again at 3700 miles. I put a gallon bottle under the reservoir hose and its been filling the bottle up with dirty diesel exponentially. Its at about 1 gallon in 3-4hrs. Safe to say I think my coolant system is mostly all diesel at this point. Overall the truck has been performing normally between 180° to 190° and 200° to 210° while PTO offloading. Just recently the fan has come on and will not turn off at all keeping temps at 120° to 150° whereas before the fan only came on when at about 200° to 210° offloading and on steep hills. What could be causing the constant fan on? Since I bypassed the coolant level sensor to avoid engine protect shutdown by unplugging it, in the off chance if I were to say burst a radiator hose and loose all fluid in my coolant system would this also initiate an engine protect shutdown? I do not hear a distinct miss on the idle or acceleration of the engine. Would a bad injector/s be subtle of painfully obvious on a Detroit 60? If so is there a way the mechanic can test each one once he has them out? I know more about cars and there are places you can send injectors out or do core exchanges that will clean, test, flow rate, balance and blueprint them at a fraction of new cost. Any such place like this for big trucks? Lastly is there a way to compression or leak down test a Detroit 60?

I know some of you will think I’m crazy for running like but desperate times, you know. And unless your comment is helpful or constructive I would kindly ask you to please keep those critiques to yourself. Thanks for any help you could provide.





So far these are the best prices I’ve found with part numbers



N3 Injectors 6-Pack R414703002S $2,362.58

Injector tube SS cups 23538840 $11.64 x6

Injector cup o-rings 23533147 $1.99 x6