Now we've been adequately warned. So we can now go ahead and used CLR in our heater cores knowing that we are fully aware of the risks. Thanks!

.......but why?......when there r other options.

Lawyers and CLR r both very caustic.

My $0.02 is, throw money and parts at it......as in all the parts in the entire cooling system. U know me, I despise multiple coolant drain/refills guessing at what part to replace next. Threads r few and far between that say "I've replaced the entire cooling system and it still overheats".

My house is at 65 psi with a pressure reducer, but it comes in from the street at 105-110 psi depending on the time of day. The front spigot is upstream of the pressure reducer, so it's like a fire hose. Great for cleaning mud off the Jeep. Works well on the neighbors cats as well, but you didn't hear that from me.

Because you told us not to.

Seriously, though, CLR is supposed to take the finish off copper and aluminum, so that's probably the reason why they recommend against using it. But if you've tried everything else, and the alternative is to spend a whole day pulling your dash to replace the heater core, I don't see what it could hurt. The worst that could happen is it eats through the metal and springs a leak, in which case you're no worse off than when you started.

If nothing else had worked, I'd chance it, just being sure to rinse the holy hell out of it before hooking the heater hoses back up.

I believe that's CLR's concern....not being able to totally flush it out due to the fact that both the inlet and outlet r at the top of the heater core, making it a little difficult to flush up.

Drain the radiator and add some Coolant flush <-- whatever brand suits you. Then fill remaining with water.

Drive for a few days for it to work. Drain radiator again. Fill back up with water. Drive for a little then drain again, to make sure you get the crud out. Flush you heater core also with a garden hose, use a bit of light shop air if you can 10psi.

Fill with coolant water mix and enjoy your heat. Had to do the whole thing twice to my 01 xj when i first got it. I couldnt get heat and the GF would not drive it because of the no heat.

Just my 2 cents.

the valve I have on the hose I barely open maybe halfway.