Lemmy Car Experts, I have a car that is randomly leaking coolant and need advice (Resolved)

YoBuckStopsHere@lemmy.worldbanned from sitebanned from site to Asklemmy@lemmy.ml – 63 points –

2012 Ford Focus, 155K miles, it is leaking a decent amount of coolant when my partner drives it to work but doesn't even leak a drop if I drive it to work. The mileage is the same but I don't sit in traffic. Could the extra heat from sitting in traffic be opening up a pinhole sized leak in the coolant line?

Edit: Thanks to a tip from the comments when the heat is turned on it leaks. I should be able to bypass that line pretty easy.

Thanks Kolgeirr@sh.itjust.works

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Any chance your partner uses the heater and you don't? Many cars have a heater core bypass valve that only allows coolant into the heater core when the heat is on in the cabin.

Thanks! I tried this, and it leaked. The issue is at the heater core. I'll putting together a bypass to the line that is leaking now.

Awesome! I claim victory for this thread. One more notch carved into the 1/2" ratchet.

People be jumping straight to head gaskets way too much when coolant issues arise.

So you are breaking the heater in your car and removing the defroster a safety feature? Just replace the heater core..

This is to get it to stop leaking coolant until I can change the heater core.

This seems like the best option. That or stop and go traffic is causing the coolant to over flow and leak out. Possible cooling fan issues if the problem is only in stop and go traffic whereas on the highway at constant speed it's fine.

Even with that design it would leak coolant. The bypass just prevents the flow of coolant but it should always be primed with coolant even when it isn’t flowing.

It'll be primed but not pressurized. Some leaks, especially in older rubber hoses, only leak under pressure when the swelling of the hose opens the split.

I’ve only seen bypass valves that block off one of the two heater core hoses to prevent flow but not both. Same idea as a thermostat blocks only one side of your radiator to prevent flow. So even though coolant isn’t flowing, it is heating up and pressurizing. There may be vehicles out there with an unusual design that blocks both inlet and outlet hoses to the heater core. But this isnt one of them.

Not trying to argue, just trying to share some of my knowledge as a former Ford tech.

Huh, didn't know that. Most of my wrenching has been done on older GM trucks and they used a vacuum actuated valve that cut the heater core out entirely by closing the loop under the hood, so coolant still flows by a shortened path. I'm just glad ops problem was found there. Thanks for the info!

Ya, op got it figured out thx to you that’s the important part. I just wanted to add a little clarity for the poor bastard that will come across this post after googling “Ford Focus coolant leak”.