Why does radiator fluid leak thru the slightly cracked head-gasket only when the heater is on full blast?

Answer 1

It appears you didn't listen to the answers you got yesterday...using the heater or not has nothing to do with it. If the sealer you put in didn't do it the first time, it won't fix it.

A flush should not eat out any "good quality" sealer, once it did the job.

While you may not have enough coolant in the oil yet, since it keeps going up, I'd worry about paying $1800 to $2400 for a rebuilt engine more than the $800 to $1000 for head gasket replacement.

One thing you can do, to be absolutely sure, is get a pressure test, both cold and hot engine, on the cooling system(radiator)...A good system with no leakage will hold pressure, while a head gasket leak will allow the pressure to drop. How fast it drops is a matter of how big the leak is. Try it! It may take ten minutes for it to drop, but it will drop if there is a leak anywhere.

Or wait until the oil gets milky and foamy, damaging the engine...the choice is yours.

Answer 2

I would think that it is actually leaking all the time. The cooling system wouldn't care if the fan speed is low or high. The flow through the heater core may have some affect on the flow through the head, but nothing to speak about if any. I would get the head gasket fixed before you destroy the engine. Trust me on this one, been there.

Answer 3

when you open the heater value you are changing the pressure / flow of the water in the system? with out looking

Answer 4

the pressure builds up in the radiator

Answer 5

because no object is 100% efficient so since there is room for flaw no machine will work perfectly.

Answer 6

change head-gasket

Answer 7

heat expands......cold shrinks. that simple.