this post was submitted on 10 Aug 2023
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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 [email protected]

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[–] [email protected] 39 points 1 year ago (4 children)

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.

[–] [email protected] 30 points 1 year ago (2 children)

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.

[–] [email protected] 18 points 1 year ago* (last edited 1 year ago)

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.

[–] [email protected] 1 points 1 year ago (1 children)

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

[–] [email protected] 11 points 1 year ago

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

[–] [email protected] 4 points 1 year ago

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.

[–] [email protected] 3 points 1 year ago

That is something I didn't think of!

[–] [email protected] 1 points 1 year ago (1 children)

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.

[–] [email protected] 3 points 1 year ago (1 children)

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.

[–] [email protected] 3 points 1 year ago (1 children)

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.

[–] [email protected] 2 points 1 year ago (1 children)

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!

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago)

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”.

[–] [email protected] 6 points 1 year ago (1 children)

Are you sure it's coolant? I know older focus had issues with the wiper liquid hose cracking.

[–] [email protected] 4 points 1 year ago

The coolant tank emptied out.

[–] [email protected] 5 points 1 year ago (2 children)

When coolant heats up, it can evaporate of there's a way out. Do you have any residue on the inside of your hood?

If you're experience a LOT of coolant loss it could be escaping into the engine through a falling head gasket. In this case you wouldn't see any residue on the inside of your hood.

God speed.

[–] [email protected] 4 points 1 year ago (1 children)

If its head gasket I would expect the loss to be consistent. If you open the rocker cover cap / oil filling point and it looks like there is Mayo in there, then it could be a sign the head gasket is failing.

[–] [email protected] 1 points 1 year ago

That was my first instinct, I had a 92 Dodge Daytona which had a terrible head gasket. That was what I was seeing with that. The focus looks fine. No loss of power and no backfires so I don't believe coolant is getting into the engine.

[–] [email protected] 2 points 1 year ago* (last edited 1 year ago) (1 children)

Inside hood is clean. The coolant hoses though look and feel like they are near the end of their life. I've not located where the leak is occurring, no signs of fluid on the engine block. The puddle I saw was next to the inside of the front right tire, under the coolant tank. I checked and it's leak free.

I added some stop leak to see if that solves it for now. Car only has to last another six months before we replace it and my teenager gets to deal with it.

[–] [email protected] 1 points 1 year ago* (last edited 1 year ago) (1 children)

my teenager gets to deal with it

Oh you sweet summer child

[–] [email protected] 2 points 1 year ago

Best way to learn how to work on a car, is to have a car that needs to be worked on.

[–] [email protected] 4 points 1 year ago (1 children)

I'm afraid that your partner has a coolant addiction and you need to get them checked into rehab.

On a serious note, perhaps sitting in traffic is causing the temp to increase and causing a leak. This would make me think perhaps the radiator fan isn't working properly?

[–] [email protected] 1 points 1 year ago

The fan comes on, we are in Colorado so we have thinner air.

[–] [email protected] 3 points 1 year ago* (last edited 1 year ago)

Does your partner blast the air conditioning?

Either way you should get a coolant system refresh and pressure test asap

[–] [email protected] 2 points 1 year ago (1 children)

Not a car expert, just a guy that learns how to do something when it needs to be done...

I don't know how relevant the "why" is... you've got a leak, and the easiest first step is to inspect to see if you can figure out where the leak is originating from. If you can figure it out, then fix that. If not, the next easiest might be to just replace the coolant lines. If it's still leaking after that, it could be either the radiator or a gasket.

Good luck!

[–] [email protected] 2 points 1 year ago

I haven't been able to make it leak yet. It was suggested above to try the heater, which I have the ac on. That might be why I haven't seen it leak, my partner always is cold.

[–] [email protected] 1 points 1 year ago* (last edited 1 year ago)

Yes, heat can play a role.

I’d recommend going to your local parts store (or probably Amazon) and getting UV dye specifically for the cooling system. You dump it in, run the car for a bit, then start looking with a black light (you’ll probably need to buy one of those too). The ones we use flash a bright yellow/green where the leak is originating from.

If that’s not something you’re comfortable with, call your trusted mechanic and see if they can do it.

If you’re losing a considerable amount of coolant, don’t let it go, you could be making a relatively simple repair significantly more expensive, or possibly even killing the engine, if it’s as bad as it sounds.

Also, has the vehicle ever been overheated before, or is it getting hot when she drives it?