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

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

26 comments

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 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.
- That is something I didn't think of!
- 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.
Are you sure it's coolant? I know older focus had issues with the wiper liquid hose cracking.
- The coolant tank emptied out.
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.
- 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.
  
  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.
- 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.
  
  my teenager gets to deal with it
  
  Oh you sweet summer child
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?
- The fan comes on, we are in Colorado so we have thinner air.
Does your partner blast the air conditioning?

Either way you should get a coolant system refresh and pressure test asap
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!
- 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.
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?
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