Fuel in Coolant, Cummins TSB170004

[Hamish]

Has anyone had fuel in their coolant and tried upgrading the O-rings on the bottom of their injectors as per Cummins TSB 170004 (for CM870)? This is a relatively new TSB, last updated 07-May-2019 and originally created in 2017. Few engine repair shops here have heard of it. I stumbled across it on the internet - but still can not find it on QuickServe, hmmm... Cummins did have the special O-rings in stock and I installed them and have absolutely no fuel in my coolant after working the truck for 30 hours or so.

Engine was de-mandated around 600,000km, inframed for burning oil at 880,000km (off-road and pulling super B's, 140000 lbs), and currently has around 430,000km on the inframe. Was a reman Cummins head installed during the inframe, aftermarket new were not as popular then.

Before the O-ring replacement I had to syphon about 1 inch of fuel off of the surge tank after each 15 hours of running. I ran it like this for a few weeks while I tried to figure out what to do. I discovered, prior to the repair, that 90% of the fuel stayed in the 3 gallon surge tank, while 10 % was spread throughout the other 10 gallons of coolant in the system, as determined by draining it all and skimming it off the top. No coolant in oil. After the repair I did drain, clean with Restore, flush with water, replace reservoir, cap, and coolant, and changing all hoses now.

Cost was a tiny fraction of what it would be to replace the head and so far appears to be a viable workaround for failed injector cups. As I understand it the cups and bottom injector O-rings both have to fail for fuel to get into coolant. It was less likely to get coolant into the fuel because the fuel destroyed the rad cap rubber and turned it into a zero-pressure cooling system, which was fortunate. First tested the repair in the shop running the coolant up to 210 DegF with 25 psi on the cooling system (via air hose/regulator). Running fine on the road now with a new rad cap.