Another radiator leak thread - help identify source?

[Fusion]

This is a fairly new rad (2 years old) and has this very small leak and I am unable to identify where it's coming from.
- It takes about two weeks of no driving for the expansion tank to be empty, but more than is in the exp. tank leaks out. Thus extremely hard to find the source.
- I do not see and trails from around the side mounted expansion tank. There is no visible leak when looking from the top/engine bay.

Has anyone seen coolant in this spot?
Can the expansion tank be leaking inside the black housing?

I'm deciding whether to replace the exp. tank or the whole radiator. It seems like a waste to replace the whole though, because I don't see how it could've been damaged.

[Gloff]

This is a fairly new rad (2 years old) and has this very small leak and I am unable to identify where it's coming from.
- It takes about two weeks of no driving for the expansion tank to be empty, but more than is in the exp. tank leaks out. Thus extremely hard to find the source.
- I do not see and trails from around the side mounted expansion tank. There is no visible leak when looking from the top/engine bay.

Has anyone seen coolant in this spot?
Can the expansion tank be leaking inside the black housing?

I'm deciding whether to replace the exp. tank or the whole radiator. It seems like a waste to replace the whole though, because I don't see how it could've been damaged.

I had a pinhole leak in a brand new Bosch radiator, it was in the housing behind the expansion tank. pull the tank off and check behind it. You'll see the dried coolant on there if that's where it's coming from.

[noid]

Go get a coolant pressure tester from harbor freight. Screw it onto the expansion tank and pump it up to 15-20 psi and listen/look for the leak.

[Fusion]

I don't think pressurizing the system will help since it doesn't leak more after driving (pressurized, hot) than it does standing and cold.

I guess I'll try pulling the expansion tank and inspect it and the housing around it.

[Gloff]

I don't think pressurizing the system will help since it doesn't leak more after driving (pressurized, hot) than it does standing and cold.

I guess I'll try pulling the expansion tank and inspect it and the housing around it.

Pressurizing will accelerate the leak in most cases. You pressurize a little above the operating pressure typically. Rarely, it will close the leak at the higher pressure.

You'll likely see residue where the leak is coming from once you pull the tank off. It's easier to see on the black plastic of the radiator itself, if that's where the leak is, harder to see on the white plastic of the tank if it's the tank.