Can someone tell me *why* OAT = bad for brass?

[wilshire]

I've read that the newer OAT (and HOAT too?) coolants are not good for older vehicles with lead soldered brass radiators and heater cores.

Why is this? Does the mix fail to adequately protect or is there something about it that actually attacks the solder? Is it just a problem with the soldered joints or does it cause issues with the brass itself?

I've got an older Toyota truck with a brass radiator and heater core and it calls for Toyota "red" coolant, which actually seems like a HOAT (phosphate and sodium benzoate). Toyota "pink" is also a HOAT (not sure how it's any different from 'red' other than the color), as is Zerex Asian (also phosphate and sodium benzoate), which I'm considering using.

What's the deal? What can I safely put in a system with lead solder and why?

 

[Chris142]

I cant tell you why it makes them leak but it does. Our radiator core suppliers will not warranty a leaking core if OAT was used in it.

I suspect that it does not protect the solder. When OAT is used in one they leak everywhere there is solder such as the tube to header, tube seams and header to tank seams.

 

[nthach]

It's the triazoles that protect solder. Most OATs don't have it.

 

[Dan55]

I had a 95 Bonneville that had a brass solder radiator with Dex and you could see the solder bloom at the joints.

 

[Kestas]

I just repaired a 27 year old brass/copper radiator. Damage was corrosion confined to a soldered area at the water line. The base metal was untouched. I took it apart, cleaned the base metal, and resoldered. The radiator is back in service.

I'm not exactly sure what antifreeze was in it previously, except that it was green. I thought it was conventional greem.

 

[kasedian]

No, oats are one of the best whole grains you can get. They are very in high in fiber, iron, protein, and have unsaturated fat, that is good at lowering cholesterol. Yes they will expand, but not blow up or anything, they will just absorb some fluids until they are broken down.