Not enough trim fluid or a bigger problem?

I have a 1996 Yahama 60hp with power trim. I can trim up and down out of the water with no problem but the trim works for about 5-15 minutes after being in the water on the trim up option only. The trim down works fine and continues with a controlled down trim if actuated. I thought it was a relay issue and replaced it. I was given advice on how to check it and it is fine. When I get out of the water, I have to release the hydraulic pressure with the screw and pull the motor up manually after putting it on the trailer, having someone tighten the screw with the motor in my grasp. After the motor settles down (which is usually about half way) I try again with the switch. It usually takes only two efforts of loosening the screw and lifting the motor, but the trim up begins working again....if not I trim down to the transom saver and call it a day?!?! Am I just not topping off the fluid enough?? Is there a special way to insert fluid? I have been putting fluid and actuating the trim up and down filling with the motor propped up after several runs up and down??? Is that correct?

Re: Not enough trim fluid or a bigger problem?

raise and lower unit several times manually while filing.
Running the T&T motor will just airiate the fluid.
Owners manual should have procedure

Re: Not enough trim fluid or a bigger problem?

Thanks. I'll see what I come up with. I really like how people take the time to help others. I just found this site and love it already!