Antifreeze in fuel.

[Jack_L]

Hello gentlemen. I come to you with a dilemma that has stumped both us and the stealership. 

Our 2016 Mack granite mp7 engine,

Allison trans, is getting antifreeze in the fuel tank. 

I know this because it’s coming out of the water/fuel seperator. My mechanic is telling me that it’s the injector cups leaking back into the fuel, but that’s impossible right?

[fjh]

Nope not impossible at all! injector cup issues plague these engines with a host different symptoms! hard start ng being the main ,stalling and antifreeze consumption and fuel contamination !   So if your truck is not equipped with a fuel heater its likely a cup issue or a cracked head!

Not at all strange!

Edited February 13, 2018 by fjh

[Jack_L]

Nope not impossible at all! injector cup issues plague these engines with a host different symptoms! hard start ng being the main ,stalling and antifreeze consumption and fuel contamination !   So if your truck is not equipped with a fuel heater its likely a cup issue or a cracked head!
Not at all strange!

Just curious. How would the antifreeze feed back into the fuel from the cup? Wouldn’t the antifreeze mix with the oil too? I’ve seen cracked heads and I know what you mean about the consumption. But you get smoke out the exhaust and oil in the antifreeze.


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[fjh]

Rad is under 16 psi  pressure once the engine is shut down and there is no fuel pressure to counteract coolant pressure It can conceivably push back into the fuel rail coolant is sealed by an oring on the cup! Volvo Has had CUP issues for years and has yet found a GOOD fix!  It is a tad unusual to have your condition however Very possible! and is where the most likely place to start is!

[turckster]

Chances are there is fuel in the coolant as well. The problem is it will swell all the coolant o-rings and rubber seals including clouding up the coolant reservoir. PLUS, if coolant is in the fuel chances are the injectors may have gotten a steady diet of coolant, possibly damaging the injector internals.  It may not show up now but it will in the future. 

Edited February 14, 2018 by turckster

[Rockwell]

For what is worth, had this exact same problem on a Detroit series 60. Red coolant coming out of the fuel water separator. New cups and injectors was the cure. 

[carlotpilot]

had same problem with a c-15 cat basicily same cure

[Truck Shop]

                                    Any thing with coppers or injector/water jacket sleeves can do that, Cummins, Cat and Detroit. For the 5EK and up 3406 and C-15's use the green cat loctite 

                                    on the sleeve o-rings. The Series 60's use a large o-ring that you install in the injector bore on top of the sleeve then install the injector. The injector pushes

                                    down and seals off the top of the sleeve. I have seen old 855 Cummins push coolant mixed with fuel past the radiator cap after parking .

 

                                     Truck Shop

[Jack_L]

Thanks a lot gentlemen. I am fighting with the “stealership” right now. Their telling me it’s a bad water separator. 

[Lmackattack]

The 3406E cat I drove had injector cups fail and filled the coolant system with fuel. Had to drive 200 miles with fuel leaking (slowly) out of the over flow tank to get to the nearest shop that could make the repairs.

 

When the engine is running The fuel pressure is grater than the water pressure and the fuel is pushed past the cups into the coolant passage. as soon as you shut down the hot engine the coolant can then push back into the fuel system as it has greater pressure. its a common issue on some engines.