I COULD BE WRONG, BUT I THINK THE SMALL COOLANT RESERVOIR ON TOP AND IN THE FRONT OF THE ENGINE COMPARTMENT ON MY 2017 F250 SUPER DUTY IS THE SECONDARY COOLANT RESERVOIR. IT'S CONSTANTLY LOW ON FLUID AND EVERYTIME I FILL IT UP, I WILL FIND THAT IT HAS LEAKED OUT ONTO MY DRIVEWAY THE NEXT DAY AND IT CONTINUES TO DO SO UNTIL THE RESERVOIR IS EMPTY. THIS HAS BEEN GOING ON FOR SEVERAL MONTHS. I KEEP ADDING TO IT

A FEW MONTHS AGO, DURING THE SUMMER, MY TRUCK WAS SITTING FREQUENTLY IN THE HOT SUMMER SUN FOR CONSECUTIVE DAYS. I WAS WORKING FROM HOME ONE DAY AND I HEARD WHAT I THOUGHT WAS A PRESSURE VALVE OR SOMETHING. IT SOUNDED LIKE SOMETHING POPPED AND THEN A HIGH PITCH RUSH OF AIR FOR A FEW SECONDS. I WENT OUTSIDE BUT DID NOT SEE ANYTHING AT THE TIME. A FEW DAYS LATER, THERE WAS A PUDDLE OF COOLANT ON THE GROUND. I GOT UNDER THE TRUCK AND COULD SEE THAT IT WAS SLOWLY DRIPPING COOLANT BUT COULD NOT TELL EXACTLY WHERE THE LEAK WAS COMING FROM. I FOUND THE BLACK CAP (PHOTOS) RESTING UNDER THE LARGE RADIATOR ON THE LEFT SIDE (DRIVER SIDE) OF THE VEHICLE. MY SERVICE ENGINE LIGHT CAME ON A FEW DAYS LATER AND THE ERROR CODE WAS P026A (CHARGE AIR COOLER EFFICIENCY BELOW THRESHOLD.)

NOT SURE WHAT TO DO NOW. ANYONE HAVE ANY IDEAS?

 

I am not familiar with that cap believe it or not but I can tell you that low coolant in the secondary system will set that code and turn on the CEL. I'll snoop around a few trucks and see If I can find it.

 

I’m amazed that there is no info about that cap what so ever on the internet. I’ve searched up and down, left and right and can’t find anything on “Komi S5919”. Very odd.

Leaves me wondering if it’s something you picked up on the highway or if it’s something from an aftermarket part installed onto your truck. Did you buy the truck used?

 

I've had this problem off and on for about 2 years now. I live in north Texas and when the temperature gets and stays below freezing for a day or two, I notice a puddle of coolant in front of the front differential and right under the front steering damper/stabilizer. In fact, the coolant drips down onto the front steering damper and then onto the ground. I always keep extra coolant in my toolbox just in case but I sure would like to fix the leak.

I was able to locate where the leak is coming from and it looks like an easy fix. I believe it's a 3-way hose connector for the radiator but from what I can tell, you have to buy the entire lower radiator hose assembly.

Anyone have any recommendations where I can purchase JUST the 3-way hose assembly or suggestions on how to fix the leak? See photos.

Thanks!

Did you ever figure out the fix? i have the same problem, i live in north Florida and have a 2017 f350 i have the same exact leak. I have found 1 recommendation for a fix and that is to replace the O-ring inside if the leaking connection. the video is on YouTube and references a 14mm O-ring replacement to stop the leak. Hope this helps. i have not completed the repair myself yet.

 

@yorks_repair I haven't fixed the leak issue yet, but I think I've found the main culprit and I believe you may be right. My leak appears to be coming from the plastic connector where the lower radiator hoses are joined together. I may simply try to replace the O-ring and see if that stops the leak. Otherwise, I'll have to buy the complete lower radiator hose assembly and that is more than I'd like to spend at this point.

I did find a good YouTube channel that has lots of good information for Ford F-Series owners. The channel's called Flying Wrenches and the guy's name is Mason. See link below for his explanation on the most common places/reasons for a radiator leak on a PowerStroke.

I'll try and replace the O-ring and let you know what happens!