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Cooling SystemQuestionCommunity Starter

2016 Ford Focus — coolant slowly disappears without an obvious leak

ManualEnthusiast82Community StarterJul 23, 20262016 Ford Focus STNashville
The reservoir goes from full to low over several weeks. No puddle, oil looks normal, and I cannot find dried coolant around the hoses. Is a pressure test the next logical move? I am trying to get the facts straight before spending money.
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8 replies

GaragePilotCommunity StarterCommunity StarterJul 23, 2026permalink
Log the conditions before you spend. Get a real battery/charging test on the 2016 Ford Focus, not just resting voltage, before blaming a module. Save the big job until that test fails. On “coolant slowly disappears without an obvious leak,” that was the fork that mattered for me. This is from a 2016 Ford Focus in Nashville. Post the numbers (or the code) and people can get more specific. This is the filter I use when the thread starts repeating itself. That's my plan before I call anyone.
BoostSeller448Community StarterCommunity StarterJul 23, 2026permalink
Log the conditions before you spend. Write temp, speed, and in-gear vs coast when the 2016 Ford Focus does it — then decide on parts. That's the branch I'd chase this week. On “coolant slowly disappears without an obvious leak,” that was the fork that mattered for me. This is from a 2016 Ford Focus in Nashville. If they can't show the line item, I assume it's hiding. If your situation is the opposite, ignore me. Trying not to diagnose from the couch.
ManualEnthusiast82Community StarterCommunity StarterJul 23, 2026permalink
OP here — recorded a short video and noted speed, temp, and whether it was in gear. I'm in no rush to be a hero on it.
GaragePilotCommunity StarterCommunity StarterJul 24, 2026permalink
Ask what changed right before it started. Swap the cheap/easy piece first on the 2016 Ford Focus and see if the fault moves. If the cheap test changes it, stop and reassess. This is from a 2016 Ford Focus in Nashville. Happy to compare notes if your setup is different. Happens in gear, not in park, for what that's worth.
MarketBuyer159Community StarterCommunity StarterJul 25, 2026permalink
Same neighborhood, different next step: Get a real battery/charging test on the 2016 Ford Focus, not just resting voltage, before blaming a module. Save the big job until that test fails. This is from a 2016 Ford Focus in Nashville. That's the whole play. I'd rather pay for diagnosis than a second guess-repair.
QuietFanCommunity StarterCommunity StarterJul 25, 2026permalink
I hear you, though I'd still want a second check. Write temp, speed, and in-gear vs coast when the 2016 Ford Focus does it — then decide on parts. Don't erase codes until someone who can help has seen them. Learned this the expensive way on a previous car. I'd rather be boring and correct. Happens in gear, not in park, for what that's worth.
V8Mom154Community StarterCommunity StarterJul 25, 2026permalink
That's a good start, but I wouldn't stop there. Write temp, speed, and in-gear vs coast when the 2016 Ford Focus does it — then decide on parts. Don't erase codes until someone who can help has seen them. Learned this the expensive way on a previous car. Next check is the cheap one I can do in a driveway.
CanyonMom126Community StarterCommunity StarterJul 24, 2026permalink
Intermittent stuff lies if you only catch it once. Move a coil or plug on the 2016 Ford Focus if it's cylinder-specific and see whether the code follows. You'll know quickly if you're on the wrong tree. On “coolant slowly disappears without an obvious leak,” that was the fork that mattered for me. Was this after sitting overnight? Climate here is different, so treat that as a local data point. I'll update if anything new shows up.
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