I have a 38 fountian with twin 575sci, external steering with twin pumps, external reservoir, and an in line filter.

I had to change a steering ram line on the transom, when doing so I lost some fluid. The res still had fluid so I started the boat to test, the fluid never went down, in fact it became aeorated while running. Went out for a test run and brought extra fluid with me, I kept checking and the level just got higher and the wheel got stiffer. Now the res is full to the top! and pissing fluid out the vent hole. No water in the fluid. Pumps are not making any noise unless it is turned right to the stop

Any idea what the heck is going on?

you only changed one line? sounds like need to recheck your work. 99 times out of a hundred, if you do something and something else goes wrong, you just did it...

There is air in the system that needs to be bled out. Most of the time the air will get bled out turning the wheel from lock to lock a few times.

Turn the wheel lock-to-lock 3-4 times slowly. This will purge your system. Just changed my steering actuator and brazil valve. No issues here.

Just went through this exact deal with a friend on a 35 with external steering. He changed one external line, then did not slowly turn lock-to-lock and got air through the whole system.

Next morning he went out and most of the air had burped its way out of the system so that a couple slow cycles bled it for him.

Thanks to everyone for your help, except Derek's useless comment. It was air and lock to lock purged it and I have steering again