P/S resevoir over flows

I have been working on a conversion car for a customer, I'm part owner of a BMW speciality shop in Dallas. I did not do the conversion but I know the guy who did and he is a compotent tech, he probably has more experience with these conversions then I do as I have built my own but not worked on any others till now.
The car is having a strange problem of the P/S resevoir over flowing. The first time this happened it got the belt so slippery it came all the way off. Not sure what to do I cleaned the engine compartment and belt, filled the P/S fluid and started driving. After several miles of driving, highway, stop and go, full throttle blasts, lugging the engine around town I could not reproduce the symptom. Thought maybe the belt was to loose and that was the cause.
Guy calls me this morning and says it almost happened again. Picked up the car and drove to his house, over 15 miles, everything fine till he goes to back into his garage. Then it spits fluid, gets on hot headers, lots of smoke (this is how he knows it's happened) did not throw belt this time. He said it definately appears that it all comes out the cap.
Now his driveway is steep, very steep, he says not quite as steep as ramp in to my shop, but not far off. He pulls in foreward and no problem. Could it be the steepness of the driveway alone causing the problem? Has anyone encountered the problem of resevoir overflowing for any reason? It's a stock GM pump, mustang hydroboost, porsche master with adapter, and 944 rack still powered.
This is a great forum, saved me many times on my own car.
I tried searching but i'm not very good at it.
Thanks in advance

Might be overheating the fluid, is there a cooler installed for the power steering?

Techno Duck wrote:Might be overheating the fluid, is there a cooler installed for the power steering?

No cooler, but I thought over heating the fluid was mainly a track issue.

What pump is on the car? With the Turn 1 pump and a cooler I never had an issue.

docwyte wrote:What pump is on the car?  With the Turn 1 pump and a cooler I never had an issue.

Stock pump from '03 corvette. I run the turn 1 pump as well, no cooler, never any issues with mine.

Kink in the return line causing sudden back pressure in pump when shut off? Maybe a bad pump doing same if there is a one way valve or seal at the reservoir feed side of pump? Just random thoughts.

I have the same problem with a Turn One pump. Mine's not so bad as to get on the belt or headers, but the reservoir is soaked in fluid after every run session. I've tried a brand new cap and seal, no help. I have a cooler and fluid temps are good, not even reaching 200.

It's a common issue with the f-body guys and stock pumps too. They suggest stuff like wrapping a shop towel around the cap with a rubber band. I'm looking for other ideas too...

Rich