turn on the heater?

i know that when u turn on the heater it brings heat out of the engine......my questionis, why or how does this happen??

Because you are letting the coolant that has been sitting in the heater core go through the entire system now, and it's cooler than the radiator coolant.

Coolant circulates from the engine to the radiator and back.
The engine heats the fluid, and the radiator cools it.
and it goes round...and round...and round...
get it?

Then, when you turn on the heater, it causes the fluid to also flow through the heater-core as part of the loop.

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That's a simple explanation.
Are you looking for something specific?

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nope thats good thanx

It works because the heater core is a little radiator inside your dash panel. With another fan. Starting to overheat? Turn the heater on full hot and full fan and run the windows down - I've stopped overheating in vehicles by doing exactly that.

The principle is the same - just the direction that the heat takes is different (you don't feel the heat from the engine bay. You do feel the heat from turning the heater on.) That's it. The automotive heater is just using waste heat from the engine to heat the cabin anyhow.

Exactly - by applying the cabin heater, you allow another path for the generated heat to dissipate other than the vehicle radiator.

More paths the better for excess heat to escape when overheating.

I can drop he temp in my 87 XJ from 190 Deg. F. to about 10 degrees lower by running my heater full hot and full fan.....

I say it works damn well, within a few minutes after start-up, I am being boiled alive inside unless I turn it down.....