Spent a full day chasing a phantom coolant leak on a 6.7 Powerstroke

I had this 2015 F-250 in the bay with a slow coolant loss, no obvious puddles. My first guess was the usual suspect, the water pump, so I swapped that out. Still losing coolant. Pressure tested it, held fine cold. It wasn't until I got the truck up to full operating temp and let it idle for almost an hour that I finally saw it. A tiny, fine mist was coming from the lower radiator hose connection at the block, only when everything was hot and expanded. The factory clamp had just lost its spring over time. In my experience, you always check the easy stuff first, but this one hid until everything was heat-soaked. That simple clamp cost me about eight hours of diagnostic time. Has anyone else had a leak that only showed up under specific hot conditions like that?

3 comments

3 Comments

xenarobinson2mo ago

Man, that's a tough one. I always pressure test hot for that exact reason, doesn't a cold system sometimes hide those leaks?

the_dakota23d ago

That 6.7 clamp got me too on a '17, had me second-guessing my whole pressure tester. The_max is probably right that I could've caught it if I'd been more patient with the cold pressure test, but I'm too busy drinking coffee and hoping for the best. Eight hours and I felt like a real genius watching that little mist finally appear.

the_max2mo ago

Eight hours for a radiator hose clamp seems like a lot of time invested. Pressure testing should find that, even cold, if you do it right. Maybe the test wasn't set up for long enough or the pressure wasn't high enough. Those kinds of leaks usually leave a trace, a little crust or stain, before they get that bad.