1990 Ford F150

If it's chocolate colored, you have a cracked block(water jacket) or head. If it's strawberry, the tranny cooler tank on the radiator is cracked on the inside, check engine and trans dipsticks, this will narrow it down, one has water in it?

Dave wrote No it is white and milky.
Check dipsticks. One of them should have some antifreeze, or be white and milky, but it's a sign it's probably the trans cooler, oil will turn it brown real fast. Thanks for the point!