I had a similar problem with my 88 3sfe. Seems the radiator is lower than the head so when you fill it at the radiotor, there can be air in the head which heats up and expands when driving, thus pushing coolant into the overflow reservoir.
To fix this, simply jack up the front of the car ( or put it on a hill) so the radiator filler is higher than the head, then run the car with the radiator cap loose or off. Air trapped in the head will eventually find it's way out the filler. I had to run the car for close to an hour this way to make sure it had vacated, but once I did it, I was able to drop the car down, refill the coolant to specified levels, replace the cap and forget about it.
Hope that helps
To fix this, simply jack up the front of the car ( or put it on a hill) so the radiator filler is higher than the head, then run the car with the radiator cap loose or off. Air trapped in the head will eventually find it's way out the filler. I had to run the car for close to an hour this way to make sure it had vacated, but once I did it, I was able to drop the car down, refill the coolant to specified levels, replace the cap and forget about it.
Hope that helps