2000 Focus Heater Core Leak

Coworker’s 2000 Focus’s heater core started leaking on his 50m commute this morning. He is ready to donate the car at this point. Can anyone recommend a stop leak product (i.e. Bars) that would stop the leak without clogging the cooling system.


Ed B.

Stopleak products don’t usually clog the cooling system but the may clog the heater core. I have not used one in many years, but bars leak is pretty heavy duty, for a heater core I would have used Silverseal or Dupont. Don’t even know if they are still made.

I looked at a u-tube video and it looks like the job of replacing the heater core is too bad, at least the whole dash doesnt have to come out like most cars.

It’s very unlikely there is anything that will stop the leak without clogging the heater core at least partially. He can bypass the heater core or replace it.

Remove the radiator cap when the engine is cold.

Start the engine and let it idle until the engine is up to operating temperature.

Pour a tablespoon of ground black pepper into the radiator and install the radiator cap.

Let the engine continue to idle until the leak stops.


As I recall Mythbusters was able to successfully stop a radiator leak by just dropping the white of an egg into the cooling system. If I had that heater core problem and didn’t want to fix it the proper way, replacing the heater core, I wouldn’t put the egg white into the radiator, I’d figure out a way to put it into the intake of the heater core where the hose goes through the firewall.

I don’t recall if Mythbusters tried the pepper technique but I’ve heard that can work too.

A 2000 Focus is practically a new car in my way of thinking. It should have plenty of miles left as long as it’s had the basic routine maintenance. If it is in pretty good shape otherwise, were this my problem I’d replace the heater core is all. And it may turn out I’d discover it isn’t even the heater core that’s leaking. It might be a hose connector to the heater core has split.

Also, good idea to make sure that it isn’t the windshield or door that is leaking rain water onto the floor. My truck had what appeared to be a heater core leak one time, when it was actually some drain vents had plugged up.

Just a follow up, my coworker put in some Kseal over the weekend and the heater core is not leaking at the moment. If he gets a few more months out of it he’ll be happy. He’s driving it a few time a week to keep the mileage down on his 2015 Prius.

Ed B.