Help! I'm running standard Bravo 1 outdrives and they are doing great except...

My drive unit oil lever never changed one bit. It always stayed right at the full mark. Then we went on a Poker Run and ran hard for about 100 miles. After the ruin the fluid on the starboard motor had dropped below low mark on the reservoir so I filled it to the full mark. I filled when it was cold. Unfortunately, the only fluid I could find was Mercury Lower Unit Oil for outboards and I run Mercury High Performance. I ran the boat for a day and then didn't use the boat for about a week. When I did the fluid was way low!

There was some oil in the bilge so we figured it was the reservoir, the rubber line or the transom fitting. After much inspection it all appeared dry. We took the boat for a run with the engine cover removed and when I got it around 4500 - 5000 RPM it pumped fluid out of the reservoir, past the cap, O-Ring, and check valve! It was really under pressure! Now I know why there was oil in the bilge.

Well, I figured the two oils had mixed and caused foaming so I changed the oil and ran the boat for a weekend, and just gotdone changing it a second time. I took it out for a run and ran full throttle for a while. I had filled the reservoir just above the low mark, but when I got back to the dock and checked it, it was up near the neck of the bottle.

Could I still have residual "mixed" oil causing this? Is Merc High Performance Oil good stuff? Could the lower unit be sucking air in somewhere that would cause foaming?

The lower unit has about 50 hours on it since rebuild and I have found no signs of wear in the lower unit. No metal shavings, top gears look perfect, everyhing seems good. The unit on the other motor is fine.

Any ideas are appreciated!!

Jeff

WE LIKE MOBILE ONE 75W/90 IN THE BRAVOS IT WILL TAKE ALOT MORE HEAT AND WILL NOT FOAM AND CUTS DOWN ON WEAR BETTER ,AMSOIL WILL WORK VERY WELL ALSO !
TO CHECK FOR LEAKS WE PRESSURE TEST THE LOWER UNITS
HOPE THIS HELPS

As far as the foaming,,, make sure your resevoir cap is sealing,,, if its not this can cause foaming, switch caps from port to starboard and see if the problem moves.

Thanks. I give it a try.